chemistry chapter 3 atoms and moles. chapter 3 atoms and moles section 1 – substances are made of...

ChemistryChapter 3

Atoms and Moles

Chapter 3 Atoms and MolesSection 1 – Substances are made of atoms

The atomic Theory: states that atoms are the building blocks of all matter

What do you think an atom looks like?

Incorrect More Accurate


The Law of Definite Proportions

states that two samples of a given compound are made of the same elements in exactly the same proportions by mass regardless of thesizes or sources of the samples.

Table salt (sodium chloride) is an example that shows the law of definite proportions. Any sample of table salt consists of two elements in the following proportions by mass:

60.66% chlorine and 39.34% sodium


The Law of Conservation of Mass

states that the mass of the reactants in a reaction equals the mass of the products


The Law of Multiple Proportions

the law that states that when two elements combine to form twoor more compounds, the mass of one element that combines witha given mass of the other is in the ratio of small whole numbers


Dalton’s Atomic Theory

According to Dalton, elements are composed of only one kind ofatom and compounds are made from two or more kinds of atoms.


Dalton’s atomic theory can be summarized by the following statements:

1. All matter is composed of extremely small particles called atoms,which cannot be subdivided, created, or destroyed.

2. Atoms of a given element are identical in their physical andchemical properties.

3. Atoms of different elements differ in their physical and chemicalproperties.

4. Atoms of different elements combine in simple, whole-numberratios to form compounds.

5. In chemical reactions, atoms are combined, separated, or rearrangedbut never created, destroyed, or changed.


Because some parts of Dalton’s theory have been shown to be incorrect, his theory has been modified and expanded as scientists learn more about atoms.

Chapter 3 Atoms and Moles

For Homework:

1. Do Concept Review:

Section 1 – Substances are made of atoms

2. Read Chapter 3, Section 2 - Structure of Atoms

Chapter 3 Atoms and MolesSection 2 – Structure of Atoms

Experiments by several scientists in the mid-1800s led to the first changeto Dalton’s atomic theory.

Chapter 3 Atoms and MolesSection 2 – Structure of AtomsThe Discovery of Electrons by J.J. Thompson

Mid 1800’s

To study current, Thomson pumped most of the air out of a glass tube. He then applied a voltage to two metal plates, called electrodes, which were placed at either end of the tube. One electrode, called the anode, was attached to the positive terminal of the voltage source, so it had a positive charge. The other electrode, called a cathode, had a negativecharge because it was attached to the negative terminal of the voltage source. Thomson observed a glowing beam that came out of the cathode andstruck the anode and the nearby glass walls of the tube. So, he called theserays cathode rays. Thomson knew the rays must have come from the atoms of the cathodebecause most of the atoms in the air had been pumped out of the tube. Thomson also observed that when a small paddle wheel was placed inthe path of the rays, the wheel would turn. This observation suggested thatthe cathode rays consisted of tiny particles that were hitting the paddlesof the wheel.


Thomson’s experiments showed that a cathode ray consists of particlesthat have mass and a negative charge.


Thomson’s experiments showed that a cathode ray consists of particlesthat have mass and a negative charge. These particles are called electrons


Thomson proposed that the electrons of an atom were embedded in a Positively charged ball of matter. His picture of an atom, which is shownin was named the plum-pudding model


The Discovery of Nucleus by Ernest Rutherford1909

Rutherford’s team of researchers carried out the experiment where abeam of small, positively charged particles, called alpha particles,was directed at a thin gold foil. The team measured the angles at whichthe particles were deflected from their former straight-line paths as theycame out of the foil. Rutherford found that most of the alpha particles shot at the foil passedstraight through the foil. But a very small number of particles weredeflected, in some cases backward. He went on to reason that only a very concentrated positive charge in a tiny space within the gold atom could possibly repel the fast-moving, positively charged alpha particles enough to reverse the alpha particles’ direction of travel. Rutherford also hypothesized that the mass of this positive-chargecontaining region, called the nucleus, must be larger than the mass of thealpha particle.


This part of the model of the atom is still considered true today. The nucleus is the dense, central portion of the atom. The nucleus has all of thepositive charge, nearly all of the mass, but only a very small fraction ofThe volume of the atom.


By measuring the numbers of alpha particles that were deflected and theangles of deflection, scientists calculated the radius of the nucleus to beless than 1/10,000 of the radius of the whole atom.

If the nucleus of an atom were the size of a marble, then the whole atom would be about the size of a football stadium.


The positively charged particles that repelled the alpha particles inthe gold foil experiments and that compose the nucleus of an atom arecalled protons. The charge of a proton was calculated to be exactly equalin magnitude but opposite in sign to the charge of an electron. Laterexperiments showed that the proton’s mass is almost 2000 times the massof an electron.


About 30 years after the discovery of the electron, Irene Joliot-CurieDiscovered that when alpha particles hit a sample of beryllium, a beam that could go through almost anything was produced. The British scientist James Chadwick found that this beam was notdeflected by electric or magnetic fields. He concluded that the particles Carried no electric charge. Further investigation showed that these neutralparticles, which were named neutrons are part of all atomic nuclei


All atoms consist of protons and electrons. Most atoms also have neutrons.Protons and neutrons make up the small, dense nuclei of atoms. Theelectrons occupy the space surrounding the nucleus. For example, an oxygenatom has protons and neutrons surrounded by electrons. But thatdescription fits all other atoms, such as atoms of carbon, nitrogen, silver,and gold. Elements differ from each other in the number of protonstheir atoms contain.


Atomic Number and Mass Number

The number of protons that an atom has is known as the atom’s atomic number

The mass number is equal to the total number of particles of the nucleus, that is protons plus neutrons

Unlike the atomic number, which is the same for all atoms of an element, mass number can vary among atoms of a single element. In other words, all atoms of an element have the same number of protons, but they can have different numbers of neutrons. These atoms of the same element are called isotopes.


Calculating Proton, Electron and Neutron quantity

Proton Quantity is always equal to your atomic number.

How many protons are in a silver atom?

47 protonsWhich element has 25 protons in the nucleus?

Manganese



Neutron Quantity is always equal to your mass – atomic number

How many neutrons in an aluminum atom that has a mass of 27amu?

14 neutronsWhat is the mass of an atom of Iron that contains 30 neutrons?

56 amu



Electron Quantity using the following rules:

For neutral atom:

Electron quantity is equal to proton quantity

For positively charged atoms:

For negatively charged atoms:

Electron quantity is equal to proton quantity minus the charge

Electron quantity is equal to proton quantity plus the charge



How many electrons are in an oxygen atom with a -2 charge?

How many electron in an atom of Potassium with a +1 charge?

What is the charge of a fluorine atom with 10 electrons?

What is the charge of a titanium atom with 22 electrons?

10

18

Negative 1

Neutral


Mass Charge

Protons

Electrons

Neutrons

1 amu

0 amu

1 amu Neutral

1-

1+

How to display atoms with mass and charge

Carbon – 14 or 14C or C-14 is a carbon atom with a mass of 14amu

N-3 is a nitrogen atom with a charge of negative 3

Na+

10

22

Mass number

Atomic Number

Atomic Charge

Symbol # of Protons

# of Electrons # of Neutrons Atomic Mass AtomicNumber

Atomic Charge

Mn 18 30

54 127 53

30 67 +2

25

I

Zn

53

28

74

55 25 +7

30

-1

37

Symbol # of Protons

# of Electrons

# of Neutrons

Atomic Mass

Atomic Number

Atomic Charge

54 54 77

Sr 36 88

114 76 +4

18 8 -2

Cu 65 +2

45 58 +3

Cd 46 112

As 30 75

10 14 26

20 41 +2

146 92 +6

87 136 0

Xe 131 54 Neutral

Os

O

Rh

Mg

Ca

UFr

38 3850

76 72 190

8 10 10

29 27 36 29

42 103 45

48 48 +2

12 12 +233 +342 33

18 21 20

92 86 238

87 223 87

+2

64

All atoms of an element have the same atomic number and the same number of protons. However, atoms do not necessarily have the same number of neutrons. Atoms of the same element that have different numbers of neutrons are called isotopes

How to calculate the average atomic mass on an element.

Use the formula below:

(mass of atom1 x % quantity1) + (mass of atom2 x % quantity2) +……..Average Atomic Mass = 100

Average Atomic Mass = (204 x 1.4) + (206 x 24.1) + (207 x 22.1) + (208 x 52.4) 100

Answer = 207.2 amu

Sample QuestionsIn a sample of the element potassium, each atom has1. 19 protons 2. 20 neutrons 3. 39 protons and neutrons 4. 39 neutrons

In a sample of neutral copper, all atoms have atomic numbers which are1. the same and the atoms have the same number of electrons 2. the same, but the atoms have a different number of electrons 3. different, but the atoms have the same number of electrons 4. different and the atoms have a different number of electrons

What is the mass number of an atom which contains 28 protons, 28 electrons and 34 neutrons?1. 28 2. 56 3. 62 4. 90

Sample QuestionsWhich of the following atoms has the greatest nuclear charge?1. Al 2. Ar 3. Si 4. Na

An atom of carbon-14 contains1. 8 protons, 6 neutrons and 6 electrons 2. 6 protons, 6 neutrons and 8 electrons 3. 6 protons, 8 neutrons and 8 electrons 4. 6 protons, 8 neutrons and 6 electrons

Which particle contains the greatest number of electrons?1. Na 2. Na+ 3. F 4. F-

Sample QuestionsAn electron has a charge of1. -1 and the same mass as a proton 2. +1 and the same mass as a proton 3. -1 and a smaller mass than a proton 4. +1 and a smaller mass than a proton

What is the total number of electrons in a Cr3+ ion?1. 18 2. 21 3. 24 4. 27

A particle of matter contains six protons, seven neutrons, and six electrons. This particle must be a1. neutral carbon atom 2. neutral nitrogen atom 3. positively charged carbon ion 4. positively charged nitrogen ion

If 75.0% of the isotopes of an element have a mass of 35.0 amu and 25.0% of the isotopes have a mass of 37.0 amu, what is the atomic mass of the element?1. 35.0 amu 2. 35.5 amu 3. 36.0 amu 4. 37.0 amu

Sample Questions

Which symbol represents an isotope of carbon?

Sample QuestionsAll isotopes of a given element must have the same1. atomic mass 2. atomic number 3. mass number 4. number of neutrons

As the number of neutrons in the nucleus of a given atom of an element increases, the atomic number of that element1. decreases 2. increases 3. remains the same

Which symbols represent atoms that are isotopes of each other?

Chapter 3 Atoms and MolesSection 3 Electron Configuration

Rutherford’s Model Proposed Electron Orbits

The experiments of Rutherford’s team led to the replacement of the Plumpudding model of the atom with a nuclear model of the atom. Rutherford suggested that electrons, like planets orbiting the sun, revolve around the nucleus in circular or elliptical orbits.


Bohr’s Model Confines Electrons to Energy Levels

The Rutherford model of the atom, in turn, was replaced only twoyears later by a model developed by Niels Bohr, a Danish physicist. The Bohr model describes electrons in terms oftheir energy levels.

According to Bohr’s model, electrons can be only certain distances fromthe nucleus. Each distance corresponds to a certain quantity of energy that an electron can have.


Electrons Act Like Both Particles and Waves

In 1924, Louis de Broglie pointed out that the behavior of electrons according to Bohr’s model was similar to the behavior of waves.

The present-day model of the atom, which takes into account both the particle and wave properties of electrons. According to this model, electrons are located in regions called Orbitals around a nucleus that correspond to specific energy levels. Orbitals are regions where electrons are likely to be found. Orbitals are sometimes called electron clouds because they do not have sharp boundaries. When an orbital is drawn, it shows where electrons are most likely to be. Because electrons can be in other places, the orbital has a fuzzy boundary like a cloud.


The arrangement of electrons in an atom is usually shown by writingan electron configuration. Like all systems in nature, electrons in atoms tend to assume arrangements that have the lowest possible energies. An electron configuration of an atom shows the lowest-energy arrangementof the electrons for the element.

Electron Configurations


Principle Energy Levels (electron shells)

Name Max # of e-

1 2

2 8

3 18

4 32

5 32

6 32

7 32


Octet Rule: Atoms will gain or lose electrons to try to have only 8 electrons in the last principle energy level (electron shell). Very small atoms only need 2electrons to satisfy this rule.

Two types of electron configuration:

Ground state: When electrons are all found in the lowest possibleprinciple energy levels (electron shell).

Excited state: When one or more electrons have “jumped” to a higher principle energy level (electron shell).

Valence electrons: The electrons found in the outermost principle energy level (electron shell)


Sample Questions

Which electron configuration is correct for a sodium with a 1+ charge?1. 2-72. 2-83. 2-8-14. 2-8-2

How many electrons are in an Fe2+ ion?1. 24 2. 26 3. 28 4. 56


Sample Questions

Which ion has the same electron configuration as an H- ion?1. Cl- 2. F-

3. K+ 4. Li+

What is the total number of electrons in the valence shell of an atom of aluminum in the ground state?1. 8 2. 13 3. 3 4. 10


Sample Questions

Which element has an atom with the electron configuration 2-8-8-2?1. Mg 2. Ni 3. Ca 4. Ge

Which set of symbols represents atoms with valence electrons in the same electron shell?1. Ba, Br, Bi 2. Sr, Sn, I 3. O, S, Te 4. Mn, Hg, Cu


Sample Questions

Which symbol represents a particle that has the same total number of electrons as S2-?1. O2- 2. Si 3. Se2- 4. Ar

Which of these elements has an atom that completes the octet rule?1. Ne 2. Cl 3. Ca 4. Na


Ions: atoms that have lost or gained an electron

Cation: an atom that has lost at least one electron, thereby becoming positively charged.

Anion: an atom that has gained at least one electron, thereby becoming negatively charged.


What is the total number of valence electrons in a fluorine atom in the ground state? 1. 5 2. 2 3. 7 4. 9

Sample Questions


By 1900, scientists knew that light could be thought of as moving wavesthat have given frequencies, speeds, and wavelengths. In empty space, light waves travel at 2.998 × 108 m/s. At this speed, lightwaves take only 500 s to travel the 150 million kilometers between the sunand Earth. The wavelength is the distance between two consecutive peaksor troughs of a wave. The distance of a wavelength is usually measured inmeters. The wavelength of light can vary from 105 m to less than 10−13 m.This broad range of wavelengths makes up the electromagnetic spectrum.Our eyes are sensitive to only a small portion of the electromagnetic spectrum. This sensitivity ranges from 700 nm, which is about the value of wavelengths of red light, to 400 nm, which is about the value of wavelengths of violet light.


Normally, if an electron is in a state of lowest possible energy, it is in a ground state. If an electron gains energy, it moves to an excited state. Anelectron in an excited state will release a specific quantity of energy as itquickly “falls” back to its ground state. This energy is emitted as certainwavelengths of light, which give each element a unique line-emission spectrum.


http://jersey.uoregon.edu/vlab/elements/Elements.html




Sample Questions

The diagram shows the characteristic spectral line patterns of four elements. Also shown are spectral lines produced by an unknown substance. Which pair of elements is present in the unknown?

1. lithium and sodium 2. sodium and hydrogen 3. lithium and helium 4. helium and hydrogen


The characteristic bright-line spectrum of an element is produced when its electrons1. form a covalent bond 2. form an ionic bond 3. move to a higher energy state 4. return to a lower energy state

Sample Questions

When electrons in an atom in the excited state fall to lower energy levels, energy is1. absorbed, only 2. released, only 3. neither released nor absorbed 4. both released and absorbed


What is the electron configuration of a sulfur atom in the ground state?1. 2-4 2. 2-6 3. 2-8-4 4. 2-8-6

Which electron transition represents a gain of energy?1. from 2nd to 3rd shell 2. from 2nd to 1st shell 3. from 3rd to 2nd shell 4. from 3rd to 1st shell


Which is an electron configuration for an atom of chlorine in the excited state?1. 2-8-7 2. 2-8-8 3. 2-8-6-1 4. 2-8-7-1

Which electron configuration represents the electrons of an atom in an excited state?1. 2-4 2. 2-6 3. 2-7-2 4. 2-8-2

Chapter 3 Atoms and MolesSection 4 Counting Atoms

Obviously, atoms are so small that the gram is not a very convenient unitfor expressing their masses. Even the picogram (10−12 g) is not very useful.A special mass unit is used to express this unit has two names—the atomic mass unit (amu) and the Dalton (Da). In this class, atomic mass unit will be used.

Most samples of elements have great numbers of atoms. To make workingwith these numbers easier, chemists created a new unit called the mole(mol). A is defined as the number of atoms in exactly 12 grams ofcarbon-12.The mole is the SI unit for the amount of a substance.

Chemists use the mole as a counting unit, just as you use the dozen as acounting unit. Instead of asking for 12 eggs, you ask for 1 dozen eggs.Similarly, chemists refer to 1 mol of carbon or 2 mol of iron.


To convert between moles and grams, chemists use the molar mass of asubstance. The gram molar mass of an element is the mass in grams of one moleof the element. Molar mass has the unit grams per mol (g/mol). The mass ingrams of 1 mol of an element is numerically equal to the element’s atomicmass from the periodic table in atomic mass units.

For example, the atomic mass of copper to two decimal places is 63.55 amu. Therefore, the molar mass of copper is 63.55 g/mol. Meaning that 63.55 grams of copper is equal to 1 mole of copper.


Calculate the gram molar mass the following substances.

H2O

Bi(ClO3)3

N2O4

Ca(OH)2

Hg2S2O3

C6H12O6

CdO

(NH4)2Cr2O7

18 g/mol

459.5 g/mol

92.0 g/mol

74.1 g/mol

513.4 g/mol

180.0 g/mol

128.4 g/mol

252.0 g/mol


Converting between gram molar mass and moles.


1. How many moles in 125.0 grams of PbI2?

2. How many moles in 88.9 grams of Ne?

3. How many moles in 500 grams of H2O?

4. What is the mass of 5.6 moles of AgBr?

5. What is the mass of 8.5 moles of MgO?

6. What is the number of grams in 0.28 moles of K2O

7. Calculate the mass of 0.058 moles of Hg2S

0.27 moles4.4 moles

27.8 moles

1051.7 grams

342.6 grams

26.4 grams

25.1 grams


Scientists have also determined the number of particles present in 1 mol of a substance, called Avogadro’s number One mole of pure substancecontains 6.0221367 × 1023 particles.

Avogadro’s number may be used to count any kind of particle, includingatoms and molecules. For calculations in this class ,Avogadro’s numberwill be rounded to 6.022 × 1023 particles per mole.

Chapter 3 Atoms and Moles

HomeworkPages 107-112

Due Thursday#1-12, 15-22, 24-36, 38, 42, 43, 45

Due Friday46a-d, 48a-d, 53a-c, 54a-c,

55a-g, 56a-b, 57

Chapter 3 Atoms and MolesChapter Review

chemistry chapter 3 atoms and moles. chapter 3 atoms and moles section 1 – substances are made of...

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