Unit 2 Atomic Theory

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Unit 2Atomic Theory
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Matter

• All matter is made of atoms
• Alone as elements
• Au, Na, O, He
• In combination of elements as compounds
• H2O, NaCl, LiO2

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Early Theories of Matter

• Democritus (460-370 B.C.) proposed believed
  that
• Matter was not infinitely divisible
• Made up of tiny particles called atomos
• Atoms could not be created, destroyed, or further
  divided

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John Dalton, 19th Century

• Dalton revised Democritus's ideas based upon the
  results of scientific research he conducted
• Daltons atomic theory
• Not totally correct

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• Daltons First Atomic Theory
• Elements are made up of small indivisible
  particles called atoms
• Atoms of the same element are identical,
  different elements are different
• - (Same size, mass and chemical properties)
• Atoms are not created or destroyed in a chemical
  reaction
• A compound always has the same relative numbers
  and kinds of atoms

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What is an atom?

• An atom is the smallest particle of an element
  that retains the properties of the element

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Atomic Models

• Thomson
• Plum Pudding Model

• Rutherford
• Electron Cloud Model

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Rutherford The Nuclear Atom

• His model consisted of the following ideas
• an atom consists mostly of empty space through
  which electrons move
• electrons are held within the atom by their
  attraction to the positively charged nucleus
• small, dense, positive charged nucleus

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Bohr Model

• Based on Rutherfords model
• Adds idea of quantized energy levels

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Inside an atom subatomic particles

• These particles have mass and charge
• Nucleus holds protons neutrons
• Protons charge
• Neutrons Ø charge
• Outside of nucleus is the electron cloud
• Electron - charge

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Parts of the Atom
Name Symbol Charge Mass Location
proton p 1 1 amu nucleus
neutron n 0 1 amu nucleus
electron e- -1 0 amu outside nucleus
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Atomic Mass Unit (amu)

• Small mass s are not easy to work with, so the
  atomic mass unit (amu) was developed
• The mass of 1 amu is nearly equal to the mass of
  one proton or neutron

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Reading the Periodic Table
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Atomic Number

• The number of protons determine the element
  (ALWAYS!!!)
• Number of protons are unique to each element
• Examples
• Carbon (C) has 6 protons
• Atomic number is 6
• Copper has 29 protons
• Atomic number is 29

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Atomic Number

• In uncharged atoms, atomic number is also the
  number of electrons
• Why?
• If an atom is charged, then it is an ion
• Uncharged atom
• Atomic number of protons of electrons
• Charge protons - electrons

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Mass Number

• To find the Mass number
• protons neutrons mass number
• To find neutrons
• mass number proton (or atomic number)
  neutrons
• Mass numbers are always WHOLE s!!

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Symbols for Atoms

• X symbol of element
• A mass number
• Z number of protons
• X or X
• Can also be written element - A
• i.e. carbon - 12

A
A Z
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Mg-25 Zn atomic proton neut
ron electron mass
70 30
12
30
12
30
13
40
12
30
25
70
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Isotopes and Mass Number

• C C
• carbon-12 carbon-13
• Isotopes are atoms with the same number of
  protons but different number of neutrons

12 6
13 6
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Isotopes and Mass Number

• Example
• 3 types of Potassium
• All 3 types contain 19 protons and __ electrons
• of Protons of Neutrons Mass Number
• 19 20
• 19 21
• 19 22

19
39
40
41
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Whats the difference between mass number and
average atomic mass(weight)?

• C
• carbon-12
• But if you look on the periodic table, the number
  states 12.01
• Atomic Mass (atomic weight) a weighted average
  of the masses of all of the isotopes of that
  element. It is not the same as the mass number.

12 6
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Whats the difference between mass number and
average atomic mass?

• Mass number- specifically about one isotope
• Average atomic mass- includes the masses of all
  the different isotopes for that atom

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Mass of Individual Atoms

• Atomic mass
• The weighted average mass of the isotopes of an
  element
• Example Chlorine
• Mixture of 75.00 chlorine-35 and 25.00
  chlorine-37
• Atomic mass (0.7500)35.00 (0.2500)37.00
• 35.50 amu

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Try this one

• 3 isotopes of neon
• Ne-20 (90.92)
• Ne-21 (0.25)
• Ne-22 (8.83)
• What is the atomic mass of Ne? (add .00 to
  masses)
• (20.00)(0.9092) (21.00)(0.0025)
  (22.00)(0.0883)
• 20.17 amu

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There are two isotopes of magnesium in a
container Mg-24 and Mg-25. The mass of 121 atoms
of magnesium is 2988 amu. How many of each
isotope are present? X 37 ? 37 Mg-24 atoms Y
84 ? 84 Mg-25 atoms
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A container has 10,000. carbon atoms have a mass
of 120,110. amu. There are 2 carbon isotopes
C-12 and C-13. How many of each isotope? C-12
9890. C-13 110. The atomic weight of lithium
is 6.072 amu. There are two isotopesLi-6 and
Li-7. the mass of 151 atoms is 917 amu? How many
of each isotope? Li-6 140. Li-7 11 The mass
of one nickel is 5.13 grams, the mass of one dime
is 2.73 grams, the mass of 1 envelope is 4.38
grams. Eight coins are put into an envelope. The
mass of the envelope and coins is 38.22 grams.
How many dimes and nickels are in the
envelope? Dimes 3 Nickels 5
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• A container with a mass of 4.13 grams has a total
  of 25 dimes and quarters. The mass of a dime is
  2.73 grams, and a quarter is 7.26 grams. If the
  total mass of the container and coins is 149.39
  grams, how many dimes and how many quarters are
  there?
• Dimes 8 Q 17

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29
 
c
wl
f
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Energy of light is - directly related to the
frequency of the light - inversely related to
the wavelength. - As frequency , energy - As
wavelength , energy Energy has units of
Joules (J) E hf h Plancks constant 6.626 x
10-34 J. s
E
f
h
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What is the energy and wavelength of radiation
whose frequency is 6.775 x 1018 s-1? 3.00 x108
m/s 4.44 x10-11 m 6.775 x1018 s-1 E hf
(6.626 x10-34 Js) (6.775 x1018 s-1) 4.489
x10-15 J
 
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1. What is the wavelength of light that has a
   frequency of 2.27 x1017 s-1?
2. What is the frequency of light that has a
   wavelength of 9.13 x10-10 m?
3. What is the wavelength of light with a frequency
   of 4.27 x1018 s-1?
4. Radiation has an energy of 1.23 x10-16 J. What is
   the frequency and wavelength of the radiation?

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• wavelength 1.32 x10-9 m
• frequency 3.29 x1017 s-1
• wavelength 7.03 x10-11 m
• frequency 1.86 x1017 s-1
• wavelength 1.62 x10-9 m

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• Radioactivity when the nucleus of an atom is
  unstable causing it to decompose into another
  nucleus
• There are three types of radioactive decay
• Alpha Decay
• Beta Decay
• Gamma Decay

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Alpha Decay

• An alpha particle (a ) is produced
• An alpha particle is just a helium nucleus, He2

4 2
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Beta Decay

• An e- is kicked out of the nucleus (a neutron
  breaks up into a proton and e-), e

0 -1
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Gamma Decay

• energy is released from the nucleus
• the nucleus itself does not change, but almost
  always accompanies alpha and beta decay

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• Alpha Decay
• 23090Th ? 42He 22688Ra
• 22288Ra ?
• Beta Decay
• 23490Th ? 0-1e 23491Pa
• 13153I ?
• Gamma Decay
• 23892U ? 42He 23490Th energy

42He 21886Rn
0-1e 13154Xe
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What are the products of Po-218 after it
undergoes alpha decay followed by a beta decay,
followed by beta decay followed by alpha
decay? 21884Po ? 42He 21482Pb 21482Pb ? 0-1e
21483Bi 21483Bi ? 0-1e 21484Po 21484Po ? 42He
21082Pb
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• Half-Life (t1/2) - time required for one half of
  the original sample of nuclei to decay.
• The half-life of Ra-223 is 12 days. If you start
  with 100.0 grams of Ra-223, how much will be left
  after 36 days?
• 100.0 g ? 50.00 g ? 25.00 g ? 12.50 g
• The half life of Ra-225 is 15 minutes. If you
  have 10.0 grams now, how much did you start with
  60 minutes ago?
• 10.0 g ? 20.0 g ? 40.0 g ? 80.0 g ? 160.g

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• Fission when an atom splits into two or more
  smaller atoms in a nuclear reaction.
• 1 n U ? Kr Ba 3 n energy
• This is what takes place in a nuclear reactor or
  an atomic bomb.

92 36
235 92
141 56
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• Fusion when several smaller atoms combine to
  make a larger atom
• H H ? He 1n energy
• This is how all of the elements were created in
  nature.

2 1
3 1
4 2
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