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The Nuclear Atom

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Title: The Nuclear Atom


1
The Nuclear Atom
Atomic Scientists Song 252
2
Aristotle (460 B.C. 370 B.C.)
  • emphasized that nature consisted of four
    elements air, earth, fire, and water
  • did not believe in discontinuous or separate
    atoms, but felt that matter was continuous

3
Democritus (460 B.C. 370 B.C.)
  • first to suggest the existence of atoms (Greek
    word atomos indivisible)
  • atoms are indivisible and indestructible
  • no experimental support

http//www.stenudd.com/myth/Greek/images/democritu
s_1628_Brugghen.jpg
4
John Dalton (1766-1844)
  • used scientific method to test Democrituss ideas
  • Daltons atomic theory
  • elements composed of atoms
  • atoms of the same element are alike
  • different atoms can combine in ratios to form
    compounds
  • chemical reactions can occur when atoms are
    separated, joined, or rearranged (but atoms are
    not created nor destroyed)

5
J.J. Thompson (1856-1940)(need to know this guy)
  • discovered the electron
  • thought atom was negative charges stuck in a
    positive charged lump
  • referred to as the plumb pudding model

6
Robert A. Millikan (1868-1953)
  • found the quantity of charge carried by an
    electron (one unit of negative charge)
  • calculated the mass of an electron (1/1840th the
    mass of a hydrogen atom)

7
Ernest Rutherford (1871-1937)(need to know this
guy)
Like howitzer shells bouncing off of tissue
paper!
  • proposed that the atom is mostly empty space
  • positive charges and almost of the mass are in a
    small, centralized region called the nucleus

8
Rutherford Flash Animation
9
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10
Try it Yourself!
In the following pictures, there is a target
hidden by a cloud. To figure out the shape of the
target, we shot some beams into the cloud and
recorded where the beams came out. Can you figure
out the shape of the target?
?
11
The Answers
Target 1
Target 2
12
Niels Bohr (1855-1962)(need to know this guy)
  • electrons found only in specific circular paths
    (orbits) around the nucleus
  • based on information about how the energy of an
    atom changes when it absorbs and emits light
  • called these fixed energies energy levels

13
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14
Erwin Schrodinger (1926)
  • quantum mechanical model
  • probability of electron locations around the
    nucleus
  • not an exact orbit
  • eventually became the electron cloud model

15
Schrödinger's Cat video 141
16
Werner Heisenberg (1927)(need to know this guy)
  • Heisenberg Uncertainty Principle impossible to
    know the exact position and momentum of an
    electron at the same time
  • the observer affects the observed

http//www.deutsches-museum-bonn.de/ausstellungen/
heisenberg/bilder/heisenberg_2.jpg
17
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22
Structure of the Atom
23
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24
Particle Charge Mass (atomic mass units) Location
Proton 1 1 nucleus
Neutron Ø 1 nucleus
Electron - 1 5.0 x 10-4 (considered negligible) orbit, level, cloud
25
Carbon- 12 as a standard
  • carbon- 12
  • ALL masses on the periodic table are based on
    their relationship to carbon-12
  • the carbon- 12 isotope has been given the atomic
    weight of exactly 12.000000000 and is used as the
    basis upon which the atomic weight of other
    isotopes is determined

26
Even smaller particles
  • quarks
  • make protons neutrons
  • 6 types

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30
Learning Check
  • An atom has 14 protons and 20 neutrons.
  • A. Its atomic number is
  • 1) 14 2) 16 3) 34
  • B. Its mass number is
  • 1) 14 2) 16 3) 34
  • C. The element is
  • 1) Si 2) Ca 3) Se
  • D. The number of electrons in a neutral atom
    is
  • 1) 14 2) 6 3) 20

31
Isotopes
  • same element but differ in their number of
    neutrons
  • the atomic mass on periodic table is the WEIGHTED
    AVERAGE MASS of all the isotopes of that
    element
  • this is based on an isotopes natural abundance
  • the percentage of each isotope of an element that
    occurs in nature
  • have the same chemical properties (reactivity)
    but different physical properties (density,
    melting/boiling point)

32
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34
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35
2.3
36
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37
Chemical symbols for isotopes
  • two different ways to write isotopes
  • example for sodium
  • sodium- 23
  • only shows mass number (23) of the sodium isotope
  • 23 Na
  • shows the mass number (23) and the atomic (11)
    of the sodium isotope

11
A
Atomic Number
Z
38
Isotopes?
  • Which of the following represent isotopes of the
    same element? Which element?
  • 234 X 234 X 235 X 238 X
  • 92 93 92 92
  • 92 is the element
    uranium

39
Do You Understand Isotopes?
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
40
Radioactive Isotopes (dont need to know)
  • unstable isotopes that break down over time
  • uses
  • cobalt 60
  • radiation treatment for cancer
  • carbon 14
  • used to date objects up to 60,000
  • years old
  • iodine 125 and iodine 131
  • ingested and used for
  • medical imaging

Dangerous, but worth the risk
41
The Mass Spectrometer
42
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43
  • has many applications, but one of the simplest is
    to determine the natural abundances of the
    isotopes of a particular element
  • the relative atomic mass can be calculated from
    the data from the mass spectrometer

Mass spectrometer video (226) http//www.youtube.
com/watch?v_L4U6ImYSj0
44
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45
Calculate the relative atomic mass of magnesium
with the provided data.
  • magnesium results from the mass spectrometer
  • 80 24Mg
  • 10 25Mg
  • 10 26Mg
  • just a simple weighted mean
  • .80(24) .10(25) .10(26) 24.3 amu
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