Chapters 45: The Atom

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Chapters 4-5 The Atom

• Chemistry

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What is this a painting of?
Henri Matisse, THE BEES, 1948
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Seurat, 1884
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Pointillism
Cans Seurat, 200760x92"Depicts 106,000
aluminum cans, the number used in the US every
thirty seconds.
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Ferris Buellers Day Off
Video clip
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The Atom

• Indivisible particle of matter
• The smallest part of an element sample
• Atoms combine to form molecules compounds

Al Foil
?
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Theories Involving Matter Atoms

• Democritus (400 BC)
• atomos indivisible
• atoms are the smallest particles possible
• there are different kinds of atoms
• a very general theory
• not supported by evidence

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Aristotle (384-322 BC)

• Matter is Continuous
• Hyle a continuous substance making up all
  matter
• A philosophical theory

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Antoine Lavoisier(1743-1794)

• Law of Conservation of Mass
• Matter cannot be created nor destroyed in a
  reaction
• Mass Before Mass After
• Determined formula for water (H2O)
• Established the Metric System
• French Revolution Killed in Guillotine

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Joseph Proust(1754-1826)

• Law of Definite Composition
• Elements combine in definite ratios to form
  compounds

• Ex
• Table salt always contained 1.5 times as much
  chlorine as sodium
• Water always contained eight times as much oxygen
  as hydrogen

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John Dalton (1766-1844)

• British
• Quaker
• School Teacher
• Recorded daily weather and barometric pressure
• Color blind (called Daltonism)
• Child Prodigy

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Dalton used the work of Lavoisier and Proust to
form

• Daltons Atomic Theory (1807)
• 1) All matter is composed of atoms
• 2) Atoms of an element are alike
• 3) Each atom has its own weight
• 4) Atoms unite in definite ratios to form
  compounds

and
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Dalton used the work of Lavosier and Proust to
form
Law of Multiple Proportions
Atoms may combine in more than one ratio when
forming compounds

• i.e.
• NO 11
• NO2 12
• NO3 13

Different compounds with entirely different
properties
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Which Law is Illustrated?
Law of Definite Composition

• ____ a) Water is 89 oxygen by mass
• ____ b) 3.10 g Mg combine with 2.04 g of oxygen
  to form ___ g of magnesium oxide
• ____ c) H2O (water) H2O2 (hydrogen peroxide)

Law of Conservation of Mass
5.14
Law of Multiple Proportions
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Parts of the atom subatomic particles

• Electron (e-)
• negative charge (-1)
• discovered by JJ Thomson (1897)Nobel Prize for
  Physics in 1906
• smallest unit of electrical charge
• mass 1/1837 of a proton

J.J. Thomson (1856-1940)
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• Proton (p)
• positive charge (1)
• discovered by Ernest Rutherford
• (J.J. Thomsons student at Cavendish Labs)
• Mass 1 amu (atomic mass unit)
• Atomic Number Z p

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• Neutron (no)
• discovered in 1932 by Chadwick
• (a student of Rutherford)
• Awarded Nobel Prize for Physics in 1935
• no charge neutral
• Mass of neutron ? mass of proton

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Nucleons

• Particles in the nucleus protons neutrons
• Atomic Mass protons neutrons
• Mass Atomic Weight rounded to the nearest
  whole number

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Example
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Try This for Fluorine (F)

• Z __________
• p _________
• no _________
• e- __________
• Atomic Weight ________
• Mass ________

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Example from HW
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Isotopes

• Atoms of the same element having different masses
• same number of ________
• different number of ________

protons
neutons
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Symbolizing
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Try This
C
C
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Which is the most common isotope for Neon?

• Ne-22 or Ne-21 or Ne-20
• How do you know?

Average Atomic Weight for Ne is 20.2 g/mol
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• Why are atomic masses not whole numbers?

Atomic masses are averages of the isotopes present
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Think About It!

• An atoms weight comes from the protons and
  neutrons. The electrons are so tiny they dont
  matter for weight!
• Like a sumo wrestler weighing in with ten lady
  bugs on his shoulder. (the electrons are like
  the lady bugs, they dont change his mass very
  much).

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A practical use for Isotopes and Mass Differences

• To build an atom bomb scientists needed pure
  U-235, a tiny fraction of natural uranium
  samples.
• Separated using mass differences.

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Isotope ReviewHeavy Water

• Isotopes of hydrogen
• Hydrogen
• Deuterium
• Tritium

Deuterium Water D2O and a molecular weight of
20 g/mol
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Remember John Daltons Atom

• Dalton thought of atoms as indivisible spheres
• His proof for this was the Law of Definite
  Composition (water is H2O not H1.5O)
• He of course was wrong
• Atoms can be split into parts
• no p and e-

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Models of the AtomThomson Model
electrons
J.J. Thomson
sphere of positive charge

• Discovered the existence of the electron (1897)
• Proved Daltons idea that the atom was
  indivisible was wrong
• Thought electrons were imbedded in the atom
• Called the Plum Pudding Model

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Shortcoming of Thomsons model

• No Nucleus

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Rutherford Model

• Gold Foil Experiment (1911)
• The atom has a dense nucleus
• The atom is made of mostly empty space

click picture for video turn down volume
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Major Shortcomings of Rutherfords Model

• Electrons cannot orbit the nucleus
• they would lose energy and the atom would
  collapse

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Bohr Model

• e-s move at different levels around the nucleus

n 4 n 3 n 2 n 1
Niels Bohr 1885-1962
Click picture for video (after Lab 16 demo)
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Bohr Model of the Atom

• Energy (heat or electricity) causes e-s to move
  to higher level/excited states
• When e-s move back, energy is released in packets
  called

QUANTA
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Shortcomings of Bohr

• Only worked for the Hydrogen atom

500 Danish Kroner
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Quantum TheoryModern Model of the Atom

• Cannot be visualized
• A mathematical description of atom
• Energy is transferred in units (quanta)
• Electron position described by probability and
  quanta (packets) of energy

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Energy Levels of the Atom

• Levels
• Principal Quantum Number (n)
• Also called shell, quantum, energy level
• Horizontal Rows on the diagram on the back of
  your PT

n 1 is ground state (lowest energy level) n gt
1 is an excited state
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n 1
n 2
n 3
n 4
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Maximum e-s per energy level 2n2
2(1)2 2
2(2)2 8
2(3)2 18
2(4)2 32
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n 1
n 2
n 3
n 4
2
32
18
8
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Sublevels (l)

• Shape of the probability region of the e-
• Each energy level has n sublevels
• Circles on the diagram on the back of your PT

n 1
1 sublevel
s
2 sublevels
n 2
s, p
3 sublevels
n 3
s, p, d
4 sublevels
s, p, d, f
n 4
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n 1
n 2
n 3
n 4
2
32
18
8
s
s, p
s, p, d
s, p, d, f
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• s
• p

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Orbitals (m)
orbitals in that energy level 2n-1
The s, p, d, f circles on the diagram on the back
of your PT

• Orientation of the sublevel
• Maximum of 2 e-s per orbital
• s sublevels contain 1 orientation
• p sublevels contain 3 orientations
• d sublevels contain 5 orientations
• f sublevels contain 7 orientations

s sublevel
p sublevel
f sublevel
d sublevel
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Spin

• 2 e-s in the same orbital have opposite spin
• (opposite North and South Poles)
• Discovered in 1928
• The lines you draw in the circles on the diagram

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Electron Configurations

• 3 Simple Rules
• Electrons fill lowest energy level first
• Maximum number of 2 e- per orbital
• Orbitals half-fill before they fill
• (Each orbital gets one before an orbital can get
  seconds)

NOT
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Si 14 e-
2s2

• 1s2

2p6
3s2
3p2
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Br 35 e-

• 1s2

2s2
2p6
3s2
3p6
4s2
3d10
4p5
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Dot Diagrams

• Symbolize
• (s and p orbitals only)
• Why?

outer shell electrons

• Those are the electrons involved in bonding and
  chemical reactions

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LEFT RIGHT TOP BOTTOM
X

• Draw the dot diagram for the following

Mg
Mg 1s22s22p63s2
N
N 1s22s22p3
In
In 1s22s22p63s23p64s23d104p65s24d105p1
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Using the Periodic Table To Draw Dot Diagrams
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Lab 20
Highest s and p ONLY
nitrogen(7)
1s22s22p3
N
p
s
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Using the Periodic Table To Write Electron
Configurations
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Quiz

• 1. Write the electron configuration for
• a. Mg
• b. Co
• 2. Draw dot diagrams for
• a. Ca
• b. P
• 3. Which element has this electron configuration
• 1s22s22p5
• 4. List a difference between O2 H2 based on
  your labs.
• 5. What ion(s) make a flame with a red color?
• 6. Write the balanced equation for the
  decomposition of KClO3. Include the catalyst in
  your equation.

1s22s22p63s2
1s22s22p63s23p64s23d7
Ca
P
F
Li and Sr2
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Average Atomic Mass (Atomic Weight)

• An average of an elements isotopes
• The number seen on the periodic table

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How to Calculate Average Atomic Weight

• Na is made up of
• 95.6 Na-23 and 4.4 Na-22

(0.956) (23) (0.044) (22)

(21.988 0.968)
22.956 ? 23.0 g/mol
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Try This

• Calculate the average atomic mass of Cu
• 69.17 Cu-63 and 30.83 Cu-65

(0.6917) (63) (0.3083) (65)
43.5771 20.0395
63.6166 63.6 g/mol
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Carbon Dating

• All living things contain carbon
• There are 2 isotopes of carbon
• C-12 (stable) and C-14 (unstable)

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Age 0 Age 5700 yrs Age 11,400 yrs Age
17,100 yrs

• In living things, the ratio of C-12 C-14 is
  constant
• After an organism dies, C-14 is converted to N-14
  so the ratio changes
• Half-life of C-14, t1/2 5700 years
• Every 5700 yrs, half of the C-14 is converted to
  N-14
• By studying the ratio of fossils, ancient
  artifacts, etc. scientists can determine the age
  of objects