chapter 10: the atom · 2017-11-09 · read and discuss section 10.1: atomic structure....

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CHAPTER 10 RESOURCES

Chapter 10: The AtomTeaching Sequence Student Resources Teacher Resources

Lesson 10.1:Atomic

Structure

Three 50-minclass periods

1. Complete Chapter 10 Pretest.

2. Complete Investigation 10.1: The Atom.

3. Read and discuss Section 10.1:Atomic Structure.

Investigation 10.1 Answer Sheet

Section 10.1 Guided Reading

Skill and Practice: 10A Structure of the Atom, 10B Atoms and Isotopes, 10C The Periodic Table, 10D Ernest Rutherford

Graphic Organizer: The Atom

Investigation 10.1 Dialog

Equipment Setup: Atom Building Game

Teaching Tip: About the atom model, Average atomic mass

Lesson 10.1 Presentation Slides

Lesson 10.2:Quantum

Theory and theAtom

Two 50-minclass periods

1. Complete Investigation 10.2: Energy and the Quantum Theory.

2. Read and discuss Section 10.2:Quantum Theory and the Atom.



Skill and Practice: 10E Neils Bohr

Graphic Organizer: Nuclear Reactions




Lesson 10.3:Nuclear

Reactions

Three 50-minclass periods

1. Complete Investigation 10.3: Nuclear Reactions and Radioactivity.

2. Read and discuss Section 10.3: Nuclear Reactions.

3. Complete Chapter 10 Assessment.



Skill and Practice: 10F Radioactivity, 10G Lise Meitner, 10H Marie and Pierre Curie, 10I Rosalyn Yalow

Connection: Indirect Evidence and Archaeology



Teaching Tip: Radioactive isotopes in medicine


Chapter 10 Assessment Answer Key

Assessment Technology Resources

Student Text: Chapter 10 Assessment

ExamView® Test Bank

• Multiple Choice • Multi-format

Instructional Resources (whiteboard)

Website:

www.curiosityplace.com

PFC2_TG_2018_press.pdf 243 12/16/16 3:06 PM

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CHAPTER 10: THE ATOM

Chapter 10: Instructional ResourcesSuggested uses include whiteboard, student presentations, and support for readings and classroom lessons. Page number of the student edition (SE) is provided for animations.

Lesson 10.1 Teaching Illustrations

Animation (SE p. 261) Lesson 10.2 Teaching Illustrations

Animation (SE p. 265) Lesson 10.3 Teaching Illustrations

NGSS Connection: Chapter 10Performance ExpectationsThis chapter builds conceptual understanding and skills for the following performance expectations.

HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.

HS-PS1-8. Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.

HS-ETS1-3. Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics, as well as possible social, cultural, and environmental impacts.

Science and Engineering Practices• Developing and Using Models

Physical Science Core Ideas• Motion and its Interactions• Motion and Stability: Forces and Interactions• Waves and their Applications in Technology and

Information Transfer

These resources and more at curiosityplace.com

• Printable Student Masters• Assessment• Answer Keys• Presentation Slides

• Simulations• Science Content Videos• Equipment Setup Videos• E-books


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INVESTIGATION 10.1: THE ATOM

Investigation 10.1: The AtomScientists once believed that atoms were the smallest units of matter, but through experiments they have confirmed that atoms are made up of even smaller particles, such as protons, neutrons, and electrons. In this investigation, students use the Atom Building Game to create atom models. By doing so, students are introduced to the arrangement of particles within atoms and to other important concepts, such as atomic number, mass number, and isotopes.

Key Question

How is an atom organized?

Objectives

Students will

• build atom models;• describe the relationship between the number of protons, neutrons, and electrons in an atom to

its atomic and mass numbers; and• infer that not all atoms of an element are identical.

Setup

1. One class period is needed to complete the investigation.

2. Students work in small groups of two to three.

3. Become familiar with the Atom Building Game and its components prior to teaching the investigation.

Materials

Each group should have the following:

• Atom Building Game

atomic theory - a theory that states that all matter is comprised of tiny particles called atoms

proton - a positively charged particle found in the nucleus of an atom

electron - a low-mass particle with a negative charge that occupies the energy levels in an atom outside the nucleus

charge - a fundamental electrical property of matter that can be positive, zero, or negative; causes electrons (–) and protons (+) to attract each other

nucleus - the center core of an atom that contains protons and neutrons

strong nuclear force - the force that holds protons and neutrons together when they are very close together in the nucleus of atoms

atomic number - the number of protons that an atom contains

isotopes - atoms of the same element with different numbers of neutrons and different mass numbers

mass number - the total number of protons and neutrons in the nucleus of an atom

Students should observe general laboratory safety procedures while completing Investigation 10.1.

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UNIT 4: MATTER AND ENERGY

Teaching Investigation 10.1

1 Modeling an atom

The word atom is probably familiar to you. What are some facts you have already learned about atoms?

Some students may have very basic knowledge while others may have significant awareness about atoms. Most students will know that all matter is comprised of atoms. Allow student volunteers to share existing knowledge and record their responses. Pay close attention to students’ responses, as misconceptions may become evident.

Over time scientists have learned more and more about atoms. For example, scientists once believed that atoms were the smallest units of matter. We now know that there are even smaller particles inside atoms. The structure of the atom is the foundation for nearly all of the properties of matter we experience, and it is the topic of today’s investigation. This investigation will lead you through some challenging and fun games that illustrate how atoms are built from three particles: protons, neutrons, and electrons.

The Atom Building Game is a model for understanding the structure of the atom. In the game, colored marbles represent the three kinds of particles. The red or green marbles are protons, the blue marbles are neutrons, and the yellow marbles are electrons. Take a moment to look at the diagram in the center of the page. You can see that the atom represented in the diagram has three protons, three neutrons, and three electrons. Which particles are shown in the nucleus of the atom?

Tell students that the nucleus is the center of the atom. Point out its location on the diagram in the center of the page. The protons and neutrons are in the nucleus.

Where are the electrons located?

The electrons are located in the energy levels. There are two electrons in the first energy level and one in the second energy level.

Build the atom shown in the diagram using the correct marbles. Then, fill in the blanks in the empty periodic table box for the atom you constructed.

Have students look at the periodic table provided with the investigation handout. Ask them to locate the element lithium on the periodic table and fill in the missing numbers.

1 Modeling an atom

About the atom model

The atom model used in the investigation is based on both the Bohr atom and the more modern quantum description of the atom. The activities are designed to teach the basic ideas behind the structure of the atom. Those ideas include:

• Protons and neutrons are in the nucleus while electrons are outside the nucleus.

• The atomic number is the number of protons in the nucleus and determines which element an atom is.

• The mass number is the total number of particles in the nucleus and determines the isotope.

• Isotopes may be stable or unstable. Unstable isotopes are radioactive.

• Radioactivity occurs because the nucleus changes.• The electrons in atoms are arranged in well-defined

energy levels.• The rows in the periodic table correspond to

electrons filling the energy levels in the atom. For example, the first row of the periodic table has two elements (H and He) because the first energy level can only hold two electrons.

While the model of the atom is quite effective at illustrating these concepts, there are limits to how realistic the model is with regards to other aspects of atomic structure. For example, the nucleus of the atom is much smaller in relation to the overall size of the atom than it is in the model. If the atom were the size of the model, the nucleus would have a diameter of about one-half the thickness of a single sheet of paper.

Also, the mass difference between the yellow marbles and the red or green and blue marbles do not accurately represent the true mass differences between protons, neutrons, and electrons.

Tip!Tip!


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2 Using your model

Sample answers:

a. The number below the element symbol is the atomic number. This number tells you the element’s atomic number, or how many protons are in the nucleus of atoms of the element. Some students may also observe that the atomic number (or number of protons) is equal to the number of electrons.

b. The number or numbers above the element symbol is the mass number. It tells the total number of protons and neutrons in the nucleus. There may be more than one mass number for some elements as several isotopes may be possible, each with a different atomic mass.

c. Some elements have more than one number above the symbol because there is more than one possible composition of the nucleus. These different combinations are called isotopes. All isotopes of a particular element have the same number of protons but different numbers of neutrons. As the number of neutrons changes, the mass number of each form of the element also changes.

2 Using your model

You built the element lithium. Its chemical symbol is Li. Let’s answer the questions in Part 2 together. Who can tell me which number is below the chemical symbol?

The atomic number is below the symbol.

What does it tell you about the atom?

It tells you that lithium has three protons in its nucleus and three electrons. It also tells you that lithium is the third element on the periodic table and its atomic number is three.

The atomic number gives you quite a bit of information about the atom. You can locate any element on the periodic table if you know its atomic number because it is equal to the element number. For example, hydrogen is the first element on the periodic table and it has an atomic number equal to one. What can you tell me about hydrogen based on its atomic number?

Hydrogen has one proton and one electron.

What is the number or numbers above the element symbol called?

These numbers are the mass numbers. The mass number tells you the total number of protons and neutrons an atom has. In the example, lithium has a mass number of six.

Why do you think some elements have more than one mass number above their symbols?

Many atoms have more than one stable form in which they can exist. Lithium is an example. Each number written above an element’s chemical symbol represents one of these stable forms, called an isotope. One stable isotope of lithium has a mass number equal to six and another stable isotope has a mass number equal to seven.

An isotope is a form of an atom that has the same number of protons but a different number of neutrons. Consider the isotope of lithium with a mass number equal to seven. It is a neutral atom. How many protons, neutrons, and electrons does it have?

There are three protons and three electrons. Lithium-7 has four neutrons.


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3 The Atomic Challenge

I have two items to show you. The first item is a ring made of gold. The second item is made from a different metal, lead.

Show students both the gold (or some other precious metal, like platinum) ring and a sample of lead (many solders contain an alloy of lead and tin).

Look closely at each of the samples. Do you notice any similarities between the two?

Students share observations.

Do you think it is possible to turn the lead into the gold used in making the ring?

Students share ideas. Have students look at their periodic tables and locate both lead and gold.

Are lead and gold atoms the same? What can you tell about these atoms using information provided on the periodic table?

Students should be able to tell the number of protons, neutrons, and electrons in each atom.

You have already observed that lead and gold have different properties. Would any of you like to wear a ring made of lead?

Hopefully no one would want to wear a ring made of lead. Talk to students about the dangers of lead poisoning. Students may also relate to stories about government recalls of specific items (like toys) due to manufacturers using lead-based paint.

Many years ago, during a period known as the Middle Ages, some people believed that lead could be turned into gold. This was before scientists understood about atoms and their structure. However, scientists now know that atoms are unique to elements. In other words, gold atoms make up gold and lead atoms make up lead. What type of atoms do you think are found in a block of iron?

A block of iron is comprised of iron atoms.

This is true. Any element is made up of atoms of that element. Billions of years ago, only a few types of atoms existed. Look at your periodic tables for a moment. If I told you that the few types of atoms represented only three elements, which three elements would you guess?

Allow students time to think about the question and make conjecture. If no one guesses correctly then share the answer.

The three elements are hydrogen, helium, and lithium. Why do you think this is so?

Students may observe that these are the first elements on the periodic table. They are the lightest elements, have the lowest atomic numbers, fewest number of nuclei in stable forms, and are lightest in mass.

Those are good observations. In previous science classes, you may have learned about stars and a specific type of reaction that occurs within stars. A star is a big, hot ball of gas held together by the force of gravity. This force squeezes the matter at the core of stars so tightly that atoms are fused together. At high density and pressure, nuclear fusion occurs, releasing huge amounts of energy. This reaction is at the heart of how elements are created.

3 The Atomic Challenge

There are no questions to answer in Part 3.


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4 Constructing explanations

Sample answers:

a. Neon has 10 electrons.

b. Oxygen has three possible isotopes with mass numbers of 16, 17, and 18.

c. The element Technetium, symbol Tc, has no stable isotopes.

d. Iron has 26 protons in the nucleus.

e. The value given for atomic mass is an average mass based on the percentage of all isotopes and the different masses of those isotopes occurring in a typical sample of a given element.

Average atomic mass

The average atomic mass is the weighted average of stable isotopes of an element with respect to its abundance. For example, the atomic mass of magnesium on many periodic tables is given as 24.305 atomic mass units (amu).

Magnesium-24 is the most abundant isotope, with a natural abundance equal to about 79%. Magnesium-25 is only about 10% abundant, and magnesium-26 is approximately 11% abundant. Explain to students that because magnesium-24 is the most abundant isotope, it makes sense that the atomic mass listed on the periodic table is closest to 24.

Tip!Tip!

Review what students have already learned about the life cycle of stars and how the death of massive stars results in the creation of elements. There are many good resources available to support this topic. Check with your media specialist or search on the Internet for video which will help students to grasp these concepts better. Try entering a phrase such as “elements from stars” (without the quotes) in a search engine to generate some options. Students will learn more about nuclear reactions later in this chapter, so it is not necessary to delve too deeply into fusion reactions at this point. Focus more on what students already know, and use that knowledge to discuss how elements are created.

Let’s play a game: The Atomic Challenge. This is a game that simulates how the heavy elements were created inside stars. Each player on your team will take turns adding protons, neutrons, and electrons to the atom to build heavier and heavier elements.

Go over the rules for playing The Atomic Challenge. Remind students to refer to the three rules in Part 3 to ensure they have built a stable atom. Do a few practice rounds with students until they are familiar with the game.


Atoms that are not on the periodic table shown may exist in the universe but they are unstable. There are quite a few examples of this, such as the element carbon. Look at the periodic table provided. Which isotopes of carbon are shown on the periodic table?

Carbon-12 and carbon-13 are shown.

Each of these isotopes is stable. Both have six protons—carbon-12 has six neutrons and carbon-13 has seven neutrons. Carbon has a third isotope, carbon-14. It is unstable and has 8 neutrons. Does anyone know about uses for carbon-14?

Carbon-14 is used in radioactive dating of fossils and other organic materials.

Your body is made up of many different elements. What four elements make up almost all of the human body?

The elements are oxygen (65%), carbon (18%), hydrogen (10%), and nitrogen (3%). Be sure to have resources available for students to find the answer to this question.

Find the stable isotopes of oxygen. Who can find one element on the periodic table that has no stable isotopes?

Oxygen has three stable isotopes (O-16, O-17, and O-18). Technetium (Tc) has no stable isotopes.

Which element has 26 protons in its nucleus?

Iron has 26 protons in its nucleus.

On most periodic tables, a single atomic mass is listed instead of mass numbers for all stable isotopes. How is this mass related to the different isotopes?

Show students various periodic tables. Point to the average atomic mass. Students may need help answering this question. See the explanation in the Teaching Tip (right) for more details.


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Investigation 10.2: Energy and the Quantum TheoryElectrons inside atoms are limited to discrete energy states. The most convincing evidence for this unusual behavior is that atoms only emit light of certain specific energies. In this investigation, students use the Atom Building Game in conjunction with “pump” and “laser” cards that mimic photons of different colored light. By playing the game of photons and lasers, students simulate the absorption and emission of light from an atom. As they reflect on this activity, students learn that quantum physics is the branch of science that deals with extremely tiny systems such as how electrons behave inside of an atom.

Key Question

How do atoms absorb and emit light energy?

Objectives

Students will

• distinguish between atoms in the ground and excited states, and• use the Photon and Lasers game to simulate the absorption and emission of light from

an atom.

Setup



Materials


• Atom Building Game• Spectrometer

quantum theory - the theory that describes the behavior of matter and energy on the atomic scale

spectrum - the characteristic pattern of colors emitted by an element

spectral line - each individual line of color appearing in a spectrometer

spectrometer - a device that spreads light into its different colors

photon - the smallest possible quantity of light energy

energy levels - a set of quantum states, all at approximately the same value of energy

Pauli exclusion principle - the rule, according to quantum theory, stating that no two electrons in an atom can simultaneously occupy the same quantum state

quantum state - the discrete values of energy and momentum which are allowed for a particle as described by quantum theory

uncertainty principle - it is not possible to precisely know a particle’s position, momentum, energy, and time in a quantum system


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INVESTIGATION 10.2: ENERGY AND THE QUANTUM THEORY

Teaching Investigation 10.2 It may surprise you that the laws of physics you are learning about in this course are only approximations. For nearly every circumstance you are likely to encounter, they are very good approximations, but that does not mean they always give the correct description of what happens in all circumstances. For example, the universal law of gravitation will allow you to calculate the orbit of a planet around the Sun to better than 99.99 percent accuracy. However, near the Sun or near a black hole, the law of gravitation does not describe all of what happens. For instance, the orbit of the planet Mercury is slightly elliptical and the ellipse rotates. The rotation of the ellipse is due to the warping of space by the Sun’s gravity. Newton’s law of gravitation does not say anything about warping of space. Another theory, Einstein’s theory of general relativity, describes the warping of space and accurately predicts the rotation of Mercury’s orbit.

Newton’s law of universal gravitation is part of classical physics. Classical physics includes the laws of motion, the wave theory of light, and the laws describing electricity and magnetism. By the late 1800s, scientists started to uncover evidence that the laws of classical physics did not correctly describe what happens inside atoms, or between atoms. Gradually, a new theory was created that is called quantum mechanics. Quantum mechanics is the physics of small systems and describes in detail the processes that occur inside an atom. Today we are going to play a game that illustrates one of the stranger predictions of quantum mechanics. The game involves electrons and light, and it will help you to understand how a laser works.

1 The neon atom

Use the Atom Building Game to build a neon-20 atom. How many protons, neutrons, and electrons should this atom contain?

Neon-20 has 10 protons, 10 electrons, and 10 neutrons.

Where will you place the marbles representing the protons, neutrons, and electrons?

Monitor as students construct the atom. The protons and neutrons are placed in the center of the model (representing the nucleus) and the electrons are placed in the energy levels.

The instructions directed you to place the electrons in the lowest spaces possible? How did you decide where to place the electrons?

Encourage a few volunteers to share where they placed the electrons and the reasons why.

According to quantum mechanics, electrons in an atom can only exist in certain states. In the model, the states are represented by the pockets in the levels around the nucleus. Each quantum state can hold only one electron. In your neon atom all the quantum states in the first two rows are completely filled. This means the atom has the lowest energy it can have, like when a ball has rolled to the bottom of a valley.

Draw a valley on the board and show a ball at the top as being higher energy than a ball at the bottom. Discuss the idea that systems in nature tend to move toward the lowest energy.

1 The neon atom



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2 How atoms exchange energy

Sample answers:

a. Ground state refers to the state at which an atom has all of its electrons in the lowest energy level possible.

b. Neon’s second energy level is full, there are no spaces left for any additional electrons to fill. Because of this, neon does not bond with other elements readily and is on the rightmost edge of the periodic table. This column is reserved for other elements with full energy levels that do not bond with other atoms. These elements are known as the noble gases and considered inert.

c. This sequence represents a neon atom absorbing a photon of energy with the wavelength of red light. The electron goes to a level with a higher energy, and the increase is equal to the energy of the photon of red light.

d. This sequence represents a neon atom absorbing a photon of energy with the wavelength of yellow light. The electron goes to a level with a higher energy, and the increase is equal to the energy of the photon of yellow light.

e. When the electron moves back down one energy level, it emits a photon of light equal to the difference in energy from the higher level to the lower level. In this case the difference is one level and represented by a photon of red light.

2 How atoms exchange energy

Now suppose the atom was to get some energy, such as by absorbing some light. One of the electrons moves up to absorb and store the energy. The electrons in an atom store energy, like a battery. They do it by moving up to higher energy levels.

Take out the Photons and Lasers cards.

Sort through the Photons and Lasers cards and find a card called Pump 1. This card represents a single photon of red light. If a red photon is absorbed then you can move one electron up by one level, to any empty state. It does not matter which electron you move.

Students first find a Pump 1 card, then move one electron from the second level to the third level, simulating the absorption of a photon of red light.

The atom now has more energy that it did before. The energy is stored in the elevated electron, which can give the energy back by moving back down to the lower state it started in. What do you think happens when the electron eventually moves back down to its original level?

Students should answer that the atom gives off energy when the electron falls back down. Discuss the idea that the emitted light has the same color (energy) as the photon that was absorbed in the first place, because of conservation of energy.

Find one of the red cards called Laser 1. This card represents a photon of red light that is emitted by an atom. Move the electron back down, simulating the release of red light.

Students move the electron back down after they find the red Laser 1 card.

The atom has now returned to its lowest energy. In physics, the lowest energy configuration of the atom is called the ground state, because it is like a ball on the ground that is lower in energy than it would be up in the air. An atom with one or more electrons above the ground state is said to be in an excited state.

Revisit the valley you drew on the board earlier. Use the drawing to illustrate the point.

When light is absorbed by an atom, an electron is elevated to an excited state. The electron falls back down, and the light is re-emitted by the atom. This is the quantum description of how reflection works on the atomic level.

Most of the time, the process of emission occurs immediately after an atom has absorbed light. Certain atoms (and certain quantum states) can absorb light and hold on to the energy for an extended period of time, such as a glow-in-the-dark material that continues glowing for a long time. Suppose now that a photon of a certain energy strikes an atom that has an electron in an excited state with the same energy. The first photon stimulates the excited atom to release a photon. There are now two photons moving in the same direction with the same color. When emission of a photon from an atom is triggered by another photon, the process is called stimulated emission. Stimulated emission is how lasers work. In a laser, a large number of atoms are pumped up to excited states. The first atom that emits a photon triggers its neighbors to also emit photons. The second generation of photons trigger even more photons. The result is a cascade of emitted photons that are all moving in the same direction.


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INVESTIGATION 10.2: ENERGY AND THE QUANTUM THEORY

3 The photons and lasers game

We are now going to have fun playing a game that simulates how atoms absorb and emit light, like they do in a laser. Take out the Photons and Lasers cards and deal five cards to each player. Leave the atom set up as neon-20. In this game the electrons will move up and down, but the atom will not change otherwise.

Someone in each group should deal the cards.

As you look at the cards, you can see there are two basic types of cards—pump cards and laser cards. Among the pump cards are Pump 1, Pump 2, Pump 3, and Pump 4 cards. Each pump card played allows the player to move any single electron up the number of levels corresponding to the card. Look through your cards and raise your hand if you have a Pump 2 card.

Allow time for students to comply.

The Pump 2 card reads, “Absorb a yellow photon. Jump 2 energy levels.” This means you are allowed to move up two levels. If you played a Pump 1 card, you could move up one level. The objective of this game is to win by scoring 10 points. You score points by playing laser cards that stimulate any excited electrons in the atom to fall one or more levels and give off light.

Review the rules for the Photons and Lasers game. You will have to carefully repeat the rules for how many electrons can be “lasered” in any given turn. Players can move electrons from only one level in any turn. If there are three excited electrons on a level, then all three can be moved in the same turn, scoring three times as many points as a single electron. This is a strategy game; therefore, players must decide how “excited” the atom is allowed to get before they play their laser cards and score points.

4 Thinking about what you learned

All systems in nature want to achieve stability. Therefore, they are usually ordered to have the lowest energy possible. At different points in our discussion, we have talked about atoms in ground and excited states. How are these two different in terms of energy?

Use the questions in Part 4 to initiate whole class discussion. When thinking about question 4b, the emphasis is on how electrons within atoms are arranged so that they are able to attain the lowest energy. Three principles guide how electron orbitals are filled so accomplish this goal. The order of orbital filling is guided first by Aufbau principle, which is why electrons go to the 1s first, then 2s, and so on. Hund’s rule explains why each orbital sublevel, such as 2p, gets one electron before pairing. Finally, Pauli exclusion principle states that two electrons in an atom cannot have the same quantum numbers; and, it explains why two electrons in the same orbital must have opposite spin. Electrons create a magnetic field as they spin. The electrons within an orbital are like magnets. As they are paired, their opposing spins cancel each other out. Question 4e is a great lead-in to discussing spectral lines. Explain that dispersed white light produces a rainbow, a continuous spectrum. However, most light originating from excited atoms produces a line spectrum. The line spectrum is not continuous and is a series of colored lines. A simple spectrum, such as hydrogen, is a good starting point.

3 The photons and lasers game


4 Thinking about what you learned

Sample answers:

a. “Excited state” refers to an atom having at least one electron is a higher energy level than in its ground state. The excited state happens when an atom absorbs energy in some form.

b. The Pauli Exclusion Principle prevents two electrons from moving into the same quantum state.

c. In order of increasing energy: red, yellow, green, blue.

d. The atom could not release one photon of blue light because the excited electron would only have moved up one energy level, and to emit blue light, an electron would need to fall four levels. The atom would not have an electron in a high enough energy state to emit blue light.

e. It would not be possible to emit light in between green and blue. The atom could make blue and green light, which would give the effect of a blue-green light. By having some excited electrons drop four levels, a blue light would be emitted. By having other excited electrons drop three levels, a green light would be emitted. When both colors are present, the human eye would see the resulting color as a blue-green color called cyan. There is no level in between blue and green. This atom could also emit yellow light and red light.


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nuclear reaction - a reaction that changes the nucleus of at least one atom; may change one element into another element; involves much more energy than chemical reactions

radioactive - describes atoms which are unstable and spontaneously change into other atoms by the emission of particles and/or energy from the nucleus

radioactive decay - the spontaneous changing of the nucleus of atoms through the release of radiation

alpha decay - radioactive decay that results in an alpha particle (a helium nucleus) being emitted from the nucleus of an atom

beta decay - radioactive decay that results in a beta particle (an electron) being emitted from the nucleus of an atom

gamma decay - a process by which the nucleus of an atom emits a gamma ray

half-life - the length of time it takes for half of any sample of a radioactive isotope to change into other isotopes (or elements)


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Investigation 10.3: Nuclear Reactions and RadioactivityIn this investigation, students simulate the radioactive decay of an isotope. A set of 50 pennies is used to represent 50 atoms of a radioactive element. The pennies undergo “decay” when they land tails-up. Students are able to plot their data and then analyze the graph to determine whether or not they were able to correctly predict its attributes. Students then use the Atom Building Game to build the radioactive Carbon-14 atom. Because the field of nuclear chemistry has controversial aspects that are debated in the media and politics, students may be particularly curious about this subject. The last part of the investigation gives students the opportunity reflect on the experiments and to discuss different types of radioactive decay.

Key Question

How do nuclear changes involve energy?

Objectives

Students will

• determine the fraction of a radioactive sample that remains in its original isotope after an integer number of half lives,

• explain how probability and half life are related concepts, and• describe the three different types of radioactive decay (alpha, beta, and gamma decay).

Setup



Materials


• Atom Building Game• 50 pennies• Cup • Graph paper


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INVESTIGATION 10.3: NUCLEAR REACTIONS AND RADIOACTIVITY

Radioactive isotopes in medicine

One of the most commonly used radioactive isotopes in medicine is technetium-99m (Tc-99). The m stands for metastable, which means that it releases energy and becomes a more stable form of the isotope without changing its atomic number or mass number. Medical professionals use Tc-99m because it has a short half-life (about 6 hours) which minimizes the radiation dose to the patient and it does not emit harmful particles that could further damage cells. It is used to obtain images of and to locate tumors in organs such as the heart, lungs, and kidneys.

Many isotopes of iodine are also used in nuclear medicine. For example, iodine-123 is used in imaging and in the diagnosis of thyroid function; and iodine-125 is used for prostate and brain cancer therapy. Iodine-131 is used in both imaging of the thyroid and treatment of thyroid cancer.

Teaching Investigation 10.3How surprised would you be if on your way home from school your bus turned into three cars and a motorcycle?

Most students would be extremely surprised by such an occurrence.

Of course this is unlikely to happen; but, something similar happens with some atoms. These atoms are radioactive. Where have you heard the word radioactivity before?

Common responses may have to do with nuclear power, nuclear arms, or medical applications, such as x-rays.

Where does radioactivity come from?

Students may or may not have prior knowledge about radioactivity. If necessary, prompt students until they are able to deduce that radioactivity comes from the nucleus of the atom. When an atom is radioactive, it emits radiation in the form of alpha, beta, and/or gamma particles.

If the nucleus of an atom has too many neutrons, or is unstable for any other reason, the atom undergoes radioactive decay. The word decay means to break down; and, when this happens, the nucleus breaks down and forms a different nucleus. Almost all elements have some isotopes that are radioactive and other isotopes that are not radioactive.What is an isotope? Can you name an example?

Isotopes are atoms of the same element that have the same number of protons, but different numbers of neutrons. Carbon has 6 protons. There are three naturally-occurring isotopes of carbon. Carbon-12 has 6 protons and 6 neutrons. Carbon-13 has 6 protons and 7 neutrons. Carbon-14 has 6 protons and 8 neutrons.

Do you know which one of the carbon isotopes is radioactive?

Carbon-14 is radioactive. Have the students look at a periodic table while you describe radioactive isotopes that are used by scientists or in medicine. Students may be familiar with iodine being used to treat diseases, such as thyroid conditions. Point out that some elements, such as uranium and technetium, exist only as radioactive isotopes.

If the nucleus of an atom has too many neutrons, the atom is radioactive. For example, both Carbon-12 and Carbon-13 have stable nuclei and are not radioactive. Carbon-14 has one too many neutrons and is radioactive. Because of its unstable nucleus, Carbon-14 decays into stable Nitrogen-14, giving off radiation in the process. Radioactivity occurs because everything in nature tends to move toward lower energy. A ball rolls downhill to the lowest point. A hot cup of coffee cools down. Both are examples of systems that move from higher energy to lower energy over time. The same is true of the nucleus. A radioactive nucleus decays because the neutrons and protons have lower overall energy in the final nucleus than in the original.


240



1 Radioactivity

Not all of the atoms in a sample of a radioactive isotope decay at the same time. Which atoms undergo radioactive decay at a certain time depends on chance. It is possible to predict the average behavior of lots of atoms, but impossible to predict when any one atom will decay. The half-life is the time it takes for one half of the atoms in any sample to decay. In today’s investigation, you will simulate radioactive decay by flipping coins. Why is flipping a coin a good analogy for radioactive decay?

You cannot predict whether a specific toss will come up heads or tails. But, you can make a good prediction of the average outcome of 1,000 tosses. Since the chances are 50/50, out of 1,000 coin tosses you expect about 500 to be heads and about 500 to be tails. Since even small samples of ordinary materials contain many more then 1,000 atoms, it is possible to accurately predict the average rate of decay.

Each group has 50 pennies, which represent 50 Carbon-14 atoms. To simulate decay, you will place all of the pennies in a cup, shake them, and then spill the atoms on the table. Separate the pennies into two groups—those that land tails-up and the others which land heads-up. Count the number of pennies in each group and record the numbers in Table 1 as the result of the first toss. Place only the heads-up pennies from the first toss back into the cup, shake them, and then spill them on the table. Record the results as the second toss.

Students complete the first and second tosses. Monitor that students are placing the tails-up pennies aside so they are not accidentally mixed in with those being used in the toss.

Continue the procedure, using only the heads-up pennies for each toss until you have one or no pennies remaining. When you have only one or no pennies left, it means your atoms have all decayed.

1 Radioactivity

Sample data:

Heads up pennies Tails up pennies

Start 50 0

First toss 27 23

Second toss 16 11

Third toss 7 9

Fourth toss 3 4

Fifth toss 2 1

Sixth toss 2 0

Seventh toss 1 1

Eighth toss 0 1


241

INVESTIGATION 10.3: NUCLEAR REACTIONS AND RADIOACTIVITY


Sample answers:

a. Graph:

b. About 50% of the pennies were lost with each toss.

c. The concept of half-life is related to the experiment by demonstrating how half of the sample decays with each unit of time. One half life corresponds to each trial or toss we performed.


Look at the data you recorded in Table 1 and think about what a graph of this data would look like. The number of decayed atoms (heads-up pennies) will be plotted on the y-axis and the number of tosses will go on the x-axis. Use the graph paper to plot the data from Table 1. Be sure to title the graph and label the axes. Make the graph large enough so that you are able to see the trend. Plot all of the points and then draw smooth curve that best fits the points.

Allow students time to make their graphs. When they are finished, have them share the graphs with the entire class.

On average, what percentage of the pennies were lost on each toss? Lost means the number of pennies that landed tails-up and were removed.

Use this question to start a discussion about students’ observations. The number of pennies lost per toss should be approximately 50 percent.

How does the concept of half-life relate to the experiment with pennies? To what does one half-life correspond?

The half-life is the time it takes for one half of the atoms in any sample of radioactive atoms to decay. In the penny experiment, this is represented by the number of tosses needed to reduce the number of pennies from 50 to 25. The pennies that were “lost” represented the decayed atoms in a radioactive sample. Those pennies that were not “lost” were returned to the cup and retossed.

Now let’s try to improve our data. We can combine the data from the entire class. Why is this better than just graphing your own data?

If we combine data from all groups, we increase the size of our data set.

I’ll make a table on the board and I want everyone to come up and put their data on the table. Then, I want you to graph the class data and compare this graph with the first one you made.

Allow students time to record the data and make new graphs. The second graph should have a smoother curve than the first.

Did anyone predict what their graph would look like? This type of graph can be described as an exponential curve. If you were to plot population increases, they often exhibit exponential curves. How is half-life like population growth?

Both population and half-life data change by factors of two (doubling or halving). For example, two bacteria produce four, and four produce eight, and so forth. Radioactive decay occurs by halves.


242



3 Build a radioactive atom

Carbon-14 is one of three isotopes of carbon. The two other isotopes, Carbon-12 and Carbon-13, are stable. However, Carbon-14 is radioactive, which means it has an unstable nucleus. The stable isotopes of carbon are the most abundant. Only a tiny fraction of carbon in nature is Carbon-14. Given its notation, how many protons, neutrons, and electrons does Carbon-14 have?

Carbon-14 has 6 protons, 6 electrons, and 8 neutrons.

Use the Atom Building Game to build the radioactive Carbon-14 atom.

Monitor as students build the atom.

Remove one neutron from the nucleus. Replace it with a proton and an electron. When Carbon-14 undergoes radioactive decay, this is what happens. You can see that its nucleus is unstable.

4 Arguing from evidence

Gather resources that may be helpful to students as they answer the questions in Part 4 on their own or with other students in their groups. A second option is to use the questions to lead a guided discussion.

When Carbon-14 decays it becomes Nitrogen-14. Carbon-14 undergoes a specific type of radioactive decay called beta decay. Beta decay occurs when a neutron in the nucleus of a radioactive isotope splits into a proton and an electron. The proton remains in the nucleus but the electron is emitted. The emitted electron is called a beta particle.

Remind students how this was represented in Part 3 of the investigation when they removed the neutron from the Carbon-14 nucleus, and then replaced the neutron with a proton and an electron.

The half-life of Carbon-14 is 5,730 years. Carbon-14 is constantly produced from Nitrogen-14 atoms in the atmosphere. High energy cosmic rays, which are protons and other nuclei that come to Earth from outer space, are responsible for the change from 14C to 14N. As some of the carbon atoms combine with oxygen atoms in the atmosphere, carbon dioxide is formed and used on Earth by living things, such as plants during photosynthesis.

Discuss sources of radioactive carbon in the atmosphere.

In addition to beta decay, unstable isotopes emit two other kinds of radiation: alpha and gamma. When alpha decay occurs, a particle with two protons and two neutrons is released from an unstable nucleus. This particle is called an alpha particle. Radioactive isotopes that undergo alpha decay eject alpha particles, for example 238U becomes 234Th.

Gamma decay involves the release of high-energy, electromagnetic radiation from the nucleus of an atom. Because gamma decay involves releasing photons (gamma rays) instead of particles, the atomic and mass numbers remain unchanged.

3 Build a radioactive atom


4 Arguing from evidence

Sample answers:

a. Carbon-14 decays into Nitrogen-14 by giving off beta particles, which are electrons.

b. The average time for 50% of the Carbon-14 atoms to decay is about 5,730 years.

c. A person would watch the 50 Carbon-14 atoms for about 5,730 years for there to be 25 atoms left. This time corresponds to one trial or toss in the experiment. Each trial represented a “half-life,” the amount of time it takes for one-half of the atoms in a sample to decay.

d. Carbon-14 comes from Nitrogen-14 atoms in the upper atmosphere being bombarded by cosmic rays. The reaction that takes place causes the Nitrogen-14 atoms to turn into Carbon-14 atoms.

e. Two other types of radioactivity are alpha decay and gamma decay. Alpha decay is when an atom ejects a particle made up of two protons and two neutrons (a helium nucleus). An example of alpha decay is Uranium-238 decaying into Thorium-234. Gamma decay involves the release of high-energy, electromagnetic radiation from the nucleus of an atom. After cesium goes through alpha decay, the remaining barium nucleus is in an excited state, having too much energy. The barium nucleus goes through a gamma decay and emits a pulse of extremely high energy.

f. The rate at which atoms decay is constant for each particular substance, and will determine its half-life. Half-life is based on probability, not on predicting which atoms in a sample will decay. The amount of time given by a half-life value indicates only how long it will take for 50% of the sample to decay.


243

Chapter 10 Answers

Chapter 10 Answer Key

10.1 Section Review

1. The three subatomic particles are the proton, electron, and neutron. The proton is located in the nucleus and has a positive charge. The electron is found in energy levels in space around the nucleus and has a negative charge. The neutron is found in the nucleus and is an uncharged particle.

2. (a) Electrons are bound to the nucleus by electromagnetic force, first measured by Charles-Augustin de Coulomb. (b) The nucleus is held together by the strong nuclear force, predicted by Hideki Yukawa.

3. They are different elements because they do not have the same number of protons.

10.2 Section Review

1. A rainbow shows all of the separate colors of light. If you look through a prism at the light given off by a pure element, you see that the light does not contain all colors. You see a characteristic pattern of a few specific colors called a spectrum, which is different for different elements.

2. The energy in atoms changes in little all-or-nothing jumps called quanta. When an electron moves from a higher energy level to a lower energy level, the atom gives up the energy difference between the two levels. The energy comes out as light of a specific color.

3. Only one electron can be in the same quantum state in the same atom at the same time.

4. Probability is the likelihood of getting each possible outcome in a system.

10.3 Section Review

1.

A fusion nuclear reaction releases energy when the final nucleus has lower energy than the initial nuclei, or if the final nucleus is lower on the graph than the combining nuclei. A fission nuclear reaction releases energy when the final nuclei have an average lower energy than the initial nucleus, or are lower on the graph.

2.

3. 916 years. After 458 years, half of the sample will decay. Half of the remaining americium will decay over the next 458 years, leaving one-fourth of the original sample.

4. Answers will vary. Advantages: nuclear power plants emit low levels of carbon dioxide and generate large amounts of electrical energy. Disadvantages: nuclear power plants create highly radioactive waste which is costly to store and harmful to humans.

Connection Answers

1. Indirect evidence is a type of evidence that involves finding “traces” of something’s existence. For example, indirect evidence of the return of mountain lions to an area would include finding footprints or bits of the animal’s fur. An example of direct evidence would be a video recording that clearly shows the animal in an identifiable setting.

0 20 40 60 80 100

350

300

250

200

150

100

50

0

Ene

rgy

(×10

12 J

/kg)

Atomic number

Energy of the Nucleusvs. Atomic Number

238 23492 90U decay 4.5 billion years Thα→ →


244 UNIT 4: MATTER AND ENERGY


2. The ancient caravan roads reflected infrared radiation differently than the surrounding terrain. The infrared maps showed that the roads converged at the eastern edge of the “empty quarter,” and that is where Ubar was found.

3. Remote sensing saves time and money by pinpointing the best places to begin an excavation, and in some cases can provide a great deal of information about a sacred site without ever disturbing the soil. This allows archaeologists to study an area while respecting the culture of the people who call it home.

Understanding Vocabulary

1. isotopes

2. strong nuclear force

3. proton; neutron

4. spectral lines

5. quantum state; uncertainty principle

6. nuclear reactions

7. alpha decay

Reviewing Concepts

Section 10.11. Answers will vary by may include the following:

John Dalton’s atomic theory made several statements concerning the nature of matter, some of which has been modified. (1) Dalton’s theory: Matter is made of tiny, indivisible, and indestructible particles. By contrast, today we know that atoms can be broken down into smaller particles. (2) Dalton’s theory: Atoms of one element have identical properties. By contrast, today we know that although elements of the same type have similar chemical properties, elements may have isotopes with different nuclear properties.

2. Rutherford discovered that the atom is made up mostly of empty space and that each atom has a nucleus, a tiny hard core at the center, that contains most of the atom’s mass.

3. Protons and neutrons make up the nucleus of the atom.

4. The electron cloud takes up most of the space.

5. The strong force holding the nucleus together is much stronger than the repulsive electromagnetic force.

6. electrons: smallest size; smallest mass (9.109 × 10–28 grams), negative chargeprotons: small size (much larger than electrons); large mass (1.673 × 10–24 grams), positive chargeneutrons: small size (much larger than electrons); large mass (1.675 × 10–24 grams), neutral charge

7. electron: J. J. Thomson; proton and nucleus: E. Rutherford, H. Geiger, and E. Marsden; neutron: J. Chadwick

8. strong force: Hideki Yukawa, electromagnetic force: C-A de Coulomb, weak force: Enrico Fermi, gravitational force: Henry Cavendish

9. The atomic number identifies the number of protons in the nucleus of an atom and is unique for each element. The mass number indicates the number of protons plus neutrons in an atom and is unique for each isotope of an element.

10. Isotopes are atoms of the same element that have different mass numbers. Answers will vary for examples (e.g. C-12, C-13, and C-14).

11. The atomic mass unit is equivalent to 1/12 of the mass of the C-12 isotope. The value of one atomic mass unit is 1.66 × 10–27kg and is abbreviated as 1 amu.

Section 10.212. Each atom has a unique set of spectral lines created by the movement

of electrons within the atom; atoms can emit only certain colors of light indicating that electrons in the atom are restricted to the emission and absorption of specific values of energy.

13. A photon is a quantum of light energy, the smallest package of light energy.

14. The Bohr model explains that when an electron moves from a higher energy level to a lower level the atom gives up an amount of energy equivalent to the difference between the two energy levels. The energy manifests itself as light. The amounts of light released due to the movement of the atom’s electrons correspond to the spectral lines.


245

Chapter 10 Answers

15. Because electrons are so tiny, it is impossible to find their exact position without changing them in some way which changes their position.

16. wave function

Section 10.317. Both chemical and nuclear reactions involve rearranging particles.

Nuclear reactions change the nucleus of atoms and can, therefore, change one element into another. Chemical reactions involve the electrons but do not change the type of atoms and only rearrange atoms into different compounds. Nuclear reactions involve much more energy than chemical reactions.

18. Both reactions involve changes to the nucleus of the atoms involved. In a fusion reaction two nuclei combine or fuse together to form a single nucleus. In a fission reaction a single nucleus is broken down into smaller nuclei. Energy is released in both reactions. Fusion is the reaction responsible for the energy reaching Earth from the Sun.

19. no

20. Because nuclear reactions involve the strong nuclear force which is a much stronger force than the electromagnetic force involved in chemical reactions.

21. Table filled in:

22. The periodic table is a compilation of all known chemical elements. It organizes the elements according to their chemical properties.

23. The half-life of an element is the amount of time required for half of the mass of a radioactive isotope to decay.

24. Answers will vary. Sample answers:

a. Radioactive carbon is used to determine the age of organismsthat have died within the last 57,000 years.

b. Radiopharmaceuticals are used for treating certain illnessesincluding cancer.

c. Radioactive americium-241 is used in the manufacture ofsmoke detectors.

25. The fusion of hydrogen to produce helium and large amounts of energy is the basis for the energy Earth receives from the Sun. Plants rely on the sunlight thus produced. Animals and people eat plant products and are in this way powered by the Sun. In addition, fossil fuels are derived from the remains of plants.

Solving Problems

Section 10.11. atomic number = 7; mass number = 15; element is nitrogen

2. 30 – 14 = 16 neutrons

3. Carbon-12 has 6 protons and 6 neutrons; carbon 14 has 6 protons and 8 neutrons.

4. atomic number of oxygen = 8 = number of protons

5. Answers are:

a. 44b. 20c. calcium

6. 13

Decay Proton #change

Neutron #change

Ejected particle

Alpha decrease by 2 decrease by 2 helium-4 nucleus

Beta increase by 1 decrease by 1 electron

Gamma same same gamma ray




7.

boron

Section 10.28. Electron A emits the green photon, the higher energy photon, because

it undergoes a greater change in energy levels.

9. 1/6 (or 17%); 17 times

Section 10.310. b, f, c, e, a, d

11. Answers are:

a. fusionb. fissionc. fusion

12. It would take 3 half-lives to reduce 16 grams of radon to 2 grams of radon.3 half-lives × 3.8 days/half-life = 11.4 days

Test Practice

Section 10.1

1. d

2. a

3. c

Section 10.2

4. a

Section 10.3

5. c

6. b

7. c

8. a

9. c

10. a

Applying Your Knowledge

Section 10.11. You may wish to ask students to do additional research on the Internet

or in the library. Student answers should reflect that the Thomson model of the atom reflected his discovery of the electron, which carries a negative charge. The Rutherford model, based on his gold foil experiment, introduced the nucleus to the atomic model. The Bohr model introduced the idea that electrons have fixed amounts of energy. The Schrödinger model reflected discoveries of the wavelike nature of electrons.

2. The most challenging part of this project will be for your students to figure out how to show the electrons orbit in different energy levels. This aspect of the project makes it suitable as a group project. Students enjoy working together to solve problems such as how to accurately model an atom. Challenge them to try to be as accurate as possible. For an extra challenge, have them try to model an atom with a high atomic number.

Section 10.2 3. A website showing several alternate forms of the periodic table is:

http://www.wou.edu/las/physci/ch412/alttable.htm. Alternate forms of the periodic table have been developed because the elements form a complex pattern and there are a number of different ways of organizing and looking at them, depending upon what information about elements you need.


247

Chapter 10 Answers

4.

The lowest wavelength corresponds to the highest energy. Violet lines have the highest energy and red have the lowest. The red lines are to the left in the graphic and the blue/violet are to the right.

Section 10.3 5. Answers include:

a. Challenges include the extremely high temperatures needed, inexcess of 100 million°C, and the high pressure required in thereaction. In addition, it is very difficult to remove enoughimpurities from the plasma and the process.

b. The fuel for the reaction is abundant—hydrogen is verycommonly found on Earth. Nuclear fusion has no significantradioactive by-products. Another advantage is that the process isself-regulating and does not “runaway.”

c. Magnetic containment fusion uses magnetic fields to contain theplasma during the reaction. Any material used to confine theprocess would not withstand the high temperatures required, soby containing the plasma with magnetic fields, the reactor isprotected from high temperatures. One experimental reactorusing magnetic containment is the tokamak approach used in theTokamak Fusion Test Reactor.

Wavelength (nm) Color Energy

389 violet highest

402 violet

447 blue

471 blue green

502 green

588 yellow

668 red

707 deep red lowest




Skill and Practice Sheet Answers

10A Structure of the Atom

1. Answers are:

2. Answers are:

a. hydrogen-2: 1 proton, 1 neutronb. scandium-45: 21 protons, 24 neutronsc. aluminum-27: 13 protons, 14 neutronsd. uranium-235: 92 protons, 143 neutronse. carbon-12: 6 protons, 6 neutrons

3. Most of an atom’s mass is concentrated in the nucleus. The number of electrons and protons is the same but electrons are so light they contribute very little mass. The mass of the proton is 1,835 times the mass of the electron. Neutrons have a bit more mass than protons, but the two are so close in size that we usually assume their masses are the same.

4. Yes, it has a proton (+1) and no electrons to balance charge. Therefore, the overall charge of this atom (now called an ion) is +1.

5. This sodium atom has 10 electrons, 11 protons, and 12 neutrons.

10B Atoms and Isotopes

Part 1 Answers:

1. protium has 0 neutrons; deuterium has 1 neutron; tritium has 2 neutrons

2. Answers are:

a. 3b. Lithiumc. 7d.

Part 2 Answers:

1. Bromine-80

2. Potassium-39 has 20 neutrons.

3. Lithium-7

4. Neon-20 has 10 neutrons.

10C The Periodic Table

Note: Students use library or Internet resources to complete this skill sheet.

1. fluorine

2. argon

3. manganese

4. phosphorous

5. technetium

6. The atomic number tells the number of protons in an atom of the element.

7. iron, 55.8 amu

8. cesium, 132.9 amu

9. silicon, 28.1 amu

10. sodium, 23.0 amu

11. bismuth, 209.0 amu

What is this element?

How many electrons does

the neutral atom have?

What is the mass

number?

lithium 3 7

carbon 6 12

hydrogen 1 1

hydrogen (a radioactive isotope, 3H, called tritium)

1 3

beryllium 4 9

Li73


249

Chapter 10 Answers

12. The atomic mass tells the average mass of all known isotopes of an element, expressed in amu.

13. The atomic mass isn’t always a whole number because it is an average mass of all known isotopes.

14. The mass of an electron is too small to be significant.

15. Alkali metals

16. Any two of the following: soft, silvery, highly reactive, combines in 2:1 ratio with oxygen

17. Any three of the following: F, Cl, Br, I, At

18. They are toxic gases or liquids in pure form, highly reactive, and form salts with alkali metals.

19. In the far right column.

20. They rarely form chemical bonds with other atoms.

21. See figure, below

22. as above

23. as above

24. as above

25. as above




26. Hydrogen

27. Fluorine

28. Carbon

29. Sodium

30. Chlorine

10D Ernest Rutherford

1. Alpha particle: a particle that has two protons and two neutrons (also known as a helium nucleus). Beta particle: an electron emitted by an atom when a neutron splits into a proton and an electron.

2. For one atom to turn into another kind of atom, the number of protons in the nucleus must change. This can happen when an alpha particle is ejected (two protons are lost then) or when a neutron splits into a proton and an electron (in that case the number of protons increases by one).

3. Diagram:

4. Rutherford’s planetary model suggested that an atom consists of a tiny nucleus surrounded by a lot of empty space in which electrons orbit in fixed paths. Subsequent research has shown that electrons don’t exist in fixed orbitals. The Heisenberg uncertainty principle tells us that it is

impossible to know both an electron's position and its momentum at the same time. Scientists now discuss the probability that an electron will exist in a certain position. Computer models predict where an electron is most likely to exist, and three-dimensional shapes can be drawn to show the most likely positions. The sum of these shapes produces the charge-cloud model of the electron.

5. In the game of marbles, players “shoot” one marble at a group of marbles and then watch the deflection as collisions occur. This is a lot like what Rutherford was doing on a much, much smaller scale. Rutherford’s comment is reflective of his typical self-deprecating humor. While “playing with marbles,” he discovered the proton.

6. Answers will vary. Students may wish to write about one of the following discoveries: Rutherford first described two different kinds of particles emitted from radioactive atoms, calling them alpha and beta particles. He also proved that radioactive decay is possible. He developed the planetary model of the atom, and was the first to split an atom.

10E Niels Bohr

1. Both Rutherford and Bohr described atoms as having a tiny dense core (the nucleus) surrounded by electrons in orbit. Bohr described the nature of the electrons’ orbits in much greater detail.

2. Niels Bohr described electrons as existing in specific orbital pathways, and explained how atoms emit light.

3. In Bohr’s model of the atom, the electrons are in different energy levels. Bohr’s model of the atom is shown at right:

4. An electron absorbs energy as it jumps from an inner orbit to an outer one. When the electron falls back to the inner orbit, it releases the absorbed energy in the form of visible light.


251

Chapter 10 Answers

5. Answers will vary. You may wish to ask students to research world events from the end of World War II to Bohr’s death in 1962. Students should look for events that may have raised concerns in Bohr’s mind about the potential use/misuse of nuclear weapons. They might also choose to research Bohr’s own comments on the subject.

10F Radioactivity

1. In the answers below, “a” is alpha decay and “b” is beta decay.

2. Answers are:

a. During 11 minutes, fluorine-18 would experience 6 half-lives.

b. After 11 minutes (660 seconds), 0.16 grams would be left.

3. The amount after 28,650 years would be 0.0313m (or 1/32m) where m is the mass of the sample.

4. For one-fourth of the original mass to be left, there must have been time for two half-lives. Therefore, the half-life for this radioactive isotope is 9 months.

5. Answers are:

a. 0.8 W/m2

b. 3.6 × 1013 reactions per second

10G Lise Meitner

1. Ludwig Boltzmann was a pioneer of statistical mechanics. He used probability to describe how properties of atoms (like mass, charge, and structure) determine visible properties of matter (like viscosity and thermal conductivity).

2. They discovered protactinium. Its atomic number is 91 and atomic mass is 231.03588. It has 20 isotopes. All are radioactive.

3. The graphic at right illustrates fission (n = a neutron):

4. Some topics students may research and describe include nuclear power plants, nuclear weapons, and nuclear-powered submarines or aircraft carriers.

5. Meitner’s honors included the Enrico Fermi award, and element 109, meitnerium, named in her honor.

6. Students should include the following pieces of evidence in their letters:Meitner suggested tests to perform on the product of uranium bombardment.Meitner proved that splitting the uranium atom was energetically possible.Meitner explained how neutron bombardment caused the uranium nucleus to elongate and eventually split.

10H Marie and Pierre Curie

1. Sample answer: Marie (or Marya, as she was called) had a strong desire to learn and had completed all of the schooling available to young women in Poland. She was part of an illegal “underground university” that helped young women prepare for higher education. Perhaps her own thirst for knowledge fueled her empathy for the peasant children, who were also denied the right to an education.

a. Answers are:a→ b→ b→ a→ a→

a→ a→ a→ b→ b→

a→ b→ b→ a→

b. Answers are:b→ a→ a→ b→ a→

a→ b→ a→ a→ a→

b→ a→ b→

23892

U 23490

Th 23491

Pa 23492

U 23090

Th

22688

Ra22286

Rn 21884

Po 21482

Pb 21483

Bi

21484

Po21082

Pb 21083

Bi 21084

Po 20682

Pb

24094

Pu24095 Am 236

93Np 232

91Pa 232

92U

22890

Bi22488

Ra 22489

Ac 22087

Fr 21685

At

21283

Bi 21284

Po 20882

Pb 20883

Bi




2. Marie Curie proposed that uranium rays were an intrinsic part of uranium atoms, which encouraged physicists to explore the possibility that atoms might have an internal structure.

3. Marie and Pierre worked with uranium ores, separating them into individual chemicals. They discovered two substances that increased the conductivity of the air. They named the new substances polonium and radium.

4. Answers include nuclear physics, nuclear medicine, and radioactive dating.

5. Marie Curie thought carefully about how to balance her scientific career and the needs of her children. When the children were young, Pierre’s father lived with the family and took care of the children while their parents were working. Marie spent a great deal of time finding schools that best fit the individual needs of her children and at one point set up an alternative school where she and several friends took turns tutoring their children. When her daughters were in their teens, Marie included them in her professional activities when possible. Irene, for example, helped her mother set up mobile x-ray units for wounded soldiers during the war.

10I Rosalyn Sussman Yalow

1. There are some striking similarities in the lives of Rosalyn Yalow and Marie Curie. As young women, both were outstanding math and science students. Even though Yalow was 54 years younger than Marie Curie, both faced limited higher-education opportunities because they were women. Undaunted, each earned a doctorate degree in physics. Both Yalow and Curie’s research focused on radioactive materials. Curie’s work was at the forefront of discovery of how radiation works, while Yalow’s work was to develop a new application of radiation. Both women were particularly interested in the medical uses of radiation. Each was committed to using their scientific discoveries to promote humanitarian causes. Both women won Nobel Prizes for their work (Marie Curie won two).

2. RIA is a technique that uses radioactive molecules to measure tiny amounts of biological substances (like hormones) or certain drugs in blood or other body fluids.

3. Using RIA, they showed that adult diabetics did not always lack insulin in their blood, and that, therefore, something must be blocking their insulin’s normal action. They also studied the body’s immune system response to insulin injected into the bloodstream.

4. The issue of patents in medical research remains a hotly-debated issue in our society. Proponents of patents, especially for new drugs, claim that because very few new drugs make it through the extensive safety and effectiveness trials required for FDA approval, research costs are very high. Patents, they claim, are the only means of recouping these research costs. On the other side of the issue, critics say that the profit motive drives research into certain types of medicines—tending to be drugs for chronic illnesses, so that patients will take the drugs for a long time. Research into drugs (like new antibiotics) that are generally taken only for a short period of time tends to be less of a priority. You may wish to have students research the pros and cons of the patent system and write a position paper or hold a class discussion or debate on the topic.


chapter 10: the atom · 2017-11-09 · read and discuss section 10.1: atomic structure....

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