Title: The Nuclear Atom
1The Nuclear Atom
Atomic Scientists Song 252
2Aristotle (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
3Democritus (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
4John 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)
5J.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
6Robert 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)
7Ernest 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
8Rutherford Flash Animation
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10Try 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?
?
11The Answers
Target 1
Target 2
12Niels 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
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14Erwin Schrodinger (1926)
- quantum mechanical model
- probability of electron locations around the
nucleus - not an exact orbit
- eventually became the electron cloud model
15Schrödinger's Cat video 141
16Werner 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
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22Structure of the Atom
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24Particle 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
25Carbon- 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
26Even smaller particles
- quarks
- make protons neutrons
- 6 types
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30Learning 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
31Isotopes
- 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)
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352.3
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37Chemical 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
38Isotopes?
- 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
39Do You Understand Isotopes?
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
40Radioactive 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
41The Mass Spectrometer
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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
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45Calculate 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