Professor Lynn CominskyJoanne del Corral
Al JanulawMichelle Curtis
July 3, 2003
The Atom’s Family
NBSP Physical Science Leadership Institute
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Standard Connections Students know that all matter is made of
small particles called atoms, too small to see with the naked eye (3)
Students know that all matter is made of atoms…(5)
Students know that each element is made of one kind of atom… (5)
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Some questions about the atom What is an atom? What are the parts of an atom? How do we “see” the parts of the atom? What is the structure of the atom? Students know the structure of the atom,
and know it is composed of protons, neutrons and electrons (8)
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Atoms – the historical view Students know people once thought that earth,
wind, fire and water were the basic elements that made up all matter (3)
The Greek Empedocle (around 492-432 BC.) divided matter into four elements, that he also called "roots": earth, air, fire and water
The word "atom" comes from the greek "a-tomos" and signifies "indivisible". This notion was invented by Leucippe of Milet in 420 BC
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Atoms – the historical view
From 1000-1869, about 50 additional elements were discovered, many by alchemists, including As, Zn, P, Pt, Ni, N, O, Cl and Al.
In ancient times, many elements were known, including C, S, Cu, Ag, Au, Fe, Sn, Sb and Pb. The names of most of these are from the Latin words.
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History (continued) Mendeleyev’s periodic table (1869)
classified and sorted elements based on common chemical properties. His table had 62 known elements, and left space for 20 elements that were not yet discovered. The elements were arranged in order of atomic number.
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History (continued) The electron was discovered in 1897 by
Thomson. He imagined the atom as a “raisin pudding” with electrons stuck in a cake of positive charge
In 1912, Rutherford discovered the nucleus by doing scattering experiments. He concluded the atom was mostly empty space, with a large dense body at the center, and electrons which orbited the nucleus like planets orbit the Sun
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History (continued) Rutherford also realized that the nucleus must
contain both neutral and positively charged particles. The neutron was then discovered in 1932 by Chadwick.
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First activity – Rutherford revisited Given: a large wooden board, a mystery shape and
marbles Try to identify the shape that is hiding under the
wooden board. You can only roll marbles against the hidden object and observe the deflected paths that the marbles take. Take at least five minutes to "observe" a shape. Then do a second shape.
Place a piece of paper under the board for sketching the paths of the marbles. Then analyze this information to determine the object's actual shape.
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Rutherford activity analysis Black vertical line shows
path of incoming marble Red line shows path of
outgoing marble Green dotted line bisects
the angle made by the incoming and outgoing lines
Reflecting surface is perpendicular to bisecting line
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Questions about Rutherford activity Draw a small picture of each shape you studied in
your lab notebook. Can you tell the size of the object as well as its
shape? How could you find out whether the shape has
features that are small compared to the size of your marbles?
Without looking, how can you be sure of your conclusions?
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What Rutherford really did Rutherford shot alpha-particles (Helium nuclei) at
a thin gold foil. He found that most went right through. However, some were deflected, and a percentage of those bounced right back at him! He said that “it was like firing a cannonball at tissue paper, and having it ricochet off!”
Can you see how he concluded that the nucleus was a hard small sphere, and that most of the atom was empty space? (As opposed to a plum pudding?)
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Vocabulary Electron: negatively charged fundamental
particle Proton: positively charged fundamental
particle Neutron: uncharged fundamental particle Nucleus: small, central unit in the atom that
contains neutrons and protons Atom: smallest unit of an
element
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ELD Activities: Analogies, Imagery and Student Involvement
Rutherford simplified -- Have a small group of students (5-6) represent an atomic nucleus, by standing in a circle facing outward.
Have the rest of the students stand around at random spots, to represent the alpha particles.
Assign these students a straight path - either toward the circle or missing it.
If they bump into the circle, they should turn around and the children in the circle gently push them back to where they came from.
Some will bounce back and some will keep going.
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Publisher’s Materials
Take some time to look through the state-adopted texts to find activities relating to atoms that could be used in your classroom.
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Break – some things to think about
We all know that “opposites attract” and “like charges repel” –SO:
If electrons are negatively charged and protons are positively charged, why don’t the electrons fall into the nucleus?
?
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Standard connections Science experiments show that there are
more than 100 different types of atoms, which are presented in the periodic table of the elements (3)
Students know that the elements are organized in the periodic table by their chemical properties (5)
Students know how to use the periodic table to identify elements in simple compounds (8)
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Some questions: What is an element? Why are nuclei and atoms stable? What is a molecule?
http://www.caffeinearchive.com/images/molecule.gif
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Key Concepts and Vocabulary: Atoms, Elements and Molecules Atom: smallest unit of an element Element: any of more than 100 fundamental
substances that consist of atoms of only one kind Molecule: a collection of atoms, bound together.
Molecules can be made from only one element, such as H2 or O2
Molecules can be made from different elements, such as H2O or CO2
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Parts of an Atom
Each element in the Periodic Table has a different number of protons in its nucleus Protons have positive charge Change the number of protons change elements This is called nuclear physics
The element also has the same number of electrons Electrons have negative charge Change the number of electrons ionize the element This is called chemistry
Some elements also have neutrons Neutrons have no charge They are in the nuclei of atoms
p
e
n
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The Hydrogen Atom
• One electron orbiting a nucleus
• 1 proton = Z = atomic number
• 0 neutrons = N
• Total mass = A = Z+N =1
• Singly ionized Hydrogen is missing one electron = 1H+
• Add a neutron and you have Deuterium = 2H = D
p
e
1H
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The Helium Atom
• Two electrons orbiting a nucleus
• 2 protons = Z = atomic number
• 2 neutrons = N
• Total mass = A = Z+N =4
• Singly ionized Helium is missing one electron = 4He+
• Doubly ionized Helium is missing both electrons = particle = 4He++
p
pn
n
e
e
4He
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If Helium loses one of its protons (and one of its electrons), it becomes a different element
Isotopes and Elements
If Helium loses one of its neutrons, it becomes an isotope
p
nn
e
3He
p
pn
e
e3H (Tritium)
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History of the atom (Part 2) Following Rutherford’s planetary model of the
atom, it was realized that the attraction between the electrons and the protons should make the atom unstable
Bohr proposed a model in which the electrons would stably occupy fixed orbits, as long as these orbits had special quantized locations
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History of the atom (continued) In the Bohr model, the electron can
change orbits, accompanied by the absorption or emission of a photon of a specific color of light.
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History of the atom (continued) Modern quantum theories lead to stable
locations of electrons, which are not exact planetary orbits, but are characterized by specific quantum numbers.
Each electron shell is characterized by a different principle quantum number, usually called n.
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History of the atom (continued) In quantum theory, the
electron shells are not fixed orbits, but clouds of probability. You can’t measure the exact location of the electron.
Each electron orbital has a different shape, and no two electrons can be in the same orbital (unless they have opposite spins.)
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History of the atom (continued) The quantum rules for
the electron orbitals in an atom determine the row structure in the periodic table.
The geometry of the electron orbitals determines the structure of an atom
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History of the atom (continued): The spin of the electron is another quantum
property. In the planetary model, it is similar to the spin of the Earth on its axis. There are two choices for the orientation of the electron’s spin axis: up or down.
Some further questions: What is periodic about the periodic table? What types of chemical properties are used
to classify the elements?
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ELD Activity: Visual Imagery and Identifying elements Make a list of all the element names that
you know (e.g., Carbon, Oxygen, Silicon) What are some of the common household
items that contain these elements? Draw a picture of the items
Element Item Drawing
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Lunch puzzler How do nuclei stay together when they are
filled with positive charges?
?
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Periodic Table of the ElementsReview: What are the numbers in each box?
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Navigating the Periodic Table The rows are the “periods”
Each period starts a new shell of electrons The periods are numbered starting with 1 at
the top
The columns are the “groups” Each group has similar chemical properties The groups are numbered starting with 1 at
the left Elements with similar properties have the
same number of electrons in the outermost shell
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Electron shells and atomic structure
The first shell will hold up to two electrons. The orbital is spherical, and called 1s. The first row of the periodic table consists of 2 elements with 1s electrons.
The second (and third) rows each add eight electrons. The shells that are filled are made of a spherical orbital that holds 2 electrons, called 2s or 3s, and 3 non-spherical orbitals that hold a total 6 electrons, called 2p or 3p.
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Electron shells and atomic structure
In the fourth row of the periodic table, the 4s orbital fills first, then a new orbital, 3d, begins to be filled. It can hold 10 electrons.
p-orbitals
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Electron shells and atomic structure
What orbital is being filled in row 4 after 3d is filled?
What is the pattern that repeats in row 5?
d-orbitals
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Electron shells and atomic structure In row 6, a new type of orbital, 4f, appears in between elements 57 and 72. All the
elements with 4f electrons have very similar chemical properties. They are known as the Lanthanides (after element Z=57, Lanthanum) or rare earths.
A similar pattern repeats in row 7, with the 5f orbitals filling between elements 89 and 104. These elements also have similar chemical properties, and are called the Actinide elements (after element Z=89, Actinium).
There are 7 different f-orbitals: each can hold 2 electrons for a total of 14 in the 4f or 5f orbitals.
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Third activity: Shell structure Carbon=C Sodium=Na Neon=Ne Chlorine=Cl
How many protons and electrons do these elements have?
Draw the electron shell structure for each.
p p
p
e
e
e
Review: what is this element?
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Shell structure: thinking deeper Where are the elements with very stable outer
shells in the periodic table? What do we call them?
Where are the elements with one electron outside a filled shell?
Where are the elements that need one electron to fill their shells?
What happens when these two types of elements are combined chemically?
So, what are some rules for making molecules?
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Key concepts: Periodic Table The number of elements in each of the horizontal
rows (periods) in the periodic table, are due to the quantum rules that govern the electron orbitals.
In vertical columns (groups) in the periodic table, similar chemical properties are due to the number of electrons in filled or unfilled shells.
Completely filled shells make an atom very stable Elements with 1 or 2 electrons outside of filled
shells or with 1 or 2 missing electrons are very chemically reactive. They always try to combine with other elements that can fill their shells.
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Vocabulary Atomic number: the number of protons in
the nucleus of an element Atomic mass: the total mass in one atom of
an element Ionization: removal of electrons from an
atom Quantum: a very small discrete unit of light
or energy
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ELD Activities:Academic Language What is meant by the phrase quantum leap? Is this phrase consistent with the scientific
definition of the word quantum?
ELD Activities:Visual Imagery Use modeling clay to represent atomic
structure. Use different colors for protons, neutrons and electrons. Have the students try different combinations for different elements
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Publisher’s Materials
Take some time to look through the state-adopted texts to find activities relating to the periodic table that could be used in your classroom.
Examples: HC p. C46
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Thinking deeper: The forces in the atom Electrons are bound to nucleus by
the Coulomb (electromagnetic) force
Protons in nucleus are held together by the strong nuclear force
Neutrons can decay into protons by weak nuclear force, emitting an electron and an anti-neutrino. The weak force is also responsible for radioactivity.
F = k q1 q2
r2
n = p + e +
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Thinking deeper: The forces in the atom
Gravity and the electromagnetic forces both have infinite range but gravity is 1036 times weaker at a given distance
The strong and weak forces are both short range forces (<10-14 m)
The weak force is 10-8 times weaker than the strong force within the nucleus
There are four fundamental forces in physics.
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Standard connections Students know metals have properties in
common, such as high electrical conductivity (5)
The organization of the periodic table is based on the properties of the elements and reflects the structure of atoms. Students know how to identify regions corresponding to metals, nonmetals and inert gases (8)
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Fourth Activity: Electrical conduction
How can we tell which elements are good electrical conductors?
Are all metals good conductors? Are all good conductors metals? How can we tell which materials are good
electrical insulators? How do you think the electrons in
conductors differ from those in insulators?
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Equipment for Electrical Conduction activity
Insulated wires Batteries Bulbs Other things like rubber, wood, glass,
plastic, aluminum, paper clips, etc. Masking tape
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More questions for Electrical Conduction activity
Were you surprised by the some of the items that were conductors?
Were you surprised by some of the items that were insulators?
What did the conductors have in common? What did the insulators have in common?
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Electrical Conductors: A deeper look The best conductors are Copper (Cu), Silver
(Ag) and Gold (Au) Cu has Z=29, Ag has Z=47 and Au has Z=79 How are these electrons arranged?
29 = 2+8+8+10+1
47 = 2+8+8+18+10+1
So, why are these elements good conductors?
79 = 2+8+8+18 + 18+14+10 +1
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Key concepts: Electrical Conductors Conductors are usually (but not always) metals – they
have electrons that move easily, as they are outside filled shells
Insulators are materials that block the flow of electrons. They do not have easily removed electrons.
Metals occur where the d-orbitals are being filled in the periodic table.
When you flip the switch, individual electrons do not instantaneously move through the entire length of the wire. Rather, they quickly bump into the metal nuclei, as they slowly drift down the wire (at about 0.5 mm/sec)
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Vocabulary Conductor: material that allows the flow of
electricity
Insulator: material that blocks the flow of electricity
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ELD Activities: Academic Language Writing and talking aloud help the students to
better process information: The person who leads an orchestra or a band is
called a conductor. How is an orchestra conductor similar to an electrical conductor?
Buildings stay warm because of insulation material. How is insulation material similar to electrical insulators?
Share your ideas and opinion with a partner and write it in your journals in your own words.
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Reading connections Read this article for students about the
discovery of the electron. Read the longer article at home over the
weekend. Reading strategy:
Text to text Text to self Text to world
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Takeaway – fireworks puzzler What is the science behind the different
colors that you see when you watch the July 4 fireworks?
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Lesson Study Activities
Identify a key concept from today’s lecture for further development
Review the publisher’s materials about this key concept
Think about the best way to present this key concept in your classroom
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Resources
http://chemicool.com/ http://www.ill.fr/dif/3D-crystals/magnets.html http://perso.club-internet.fr/molaire1/e_histoire.html http://www.shodor.org/chemviz/ orbitals/sorbital.gif http://members.aol.com/ChangChem/porbital.gif http://members.aol.com/ChangChem/dorbital.gif Physics by Inquiry – L. McDermott and the PEG at U
Washington http://www.slac.stanford.edu/pubs/beamline/27/1/27-1-pais.pdf http://www.cc.oulu.fi/~kempmp/colours.html