Download Unit 3 Note Outline

History of the Atom
Democritis - Ancient Greek Philosopher used the word
Two discoveries led to the rebirth of the idea of the atom
1. Lavoisier 2. Proust (1799) This led to:
John Dalton (1803) -
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Dalton’s Atomic Theory
1. Each element is
2. All atoms of a given atom
3. Atoms are neither
4. A given compound always has the
ATOM - The
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Electrons
Ben Franklin - Experiments with
Michael Faraday - shows that
William Crookes (1870s) – creates and experiments
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J.J. Thompson
Crookes used a
Thompson (1897) was able to deflect the beam with
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The Proton
Thompson experimented with different gases in the tube
and always
Thompson then reversed the CRT and found the particle
coming from the anode
By doing careful measurements he was able to conclude
that the electron was about
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Models of the Atom
If a particle gains or loses an electron it becomes
Anion -
Cation -
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Oil Drop Experiment
Robert Millikan (1909) measured the charge
Millikan exposed oil droplets to X-rays. This caused the oil
droplets to become
Using the strength of the electric field, Millikan was able to
Millikan was awarded the
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Radioactivity
Henri Becquerel - discovered
Radioactivity - The spontaneous emmission of
Much of the work to describe the three basic radioactive
particles was done by
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Radioactive Particles
Radioactive Particle
Alpha
Beta
Gamma
Symbol
Charge
Mass (AMU)
Characteristic
Penetrating Ability
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Rutherford’s Experiments
1909 - Ernest Rutherford used a material that emitted
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Inside the Atom
Most of the α-particles went
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The Rutherford Atom
Rutherford concluded that most of the atom was
Around the nucleus, Rutherford thought the
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The Neutron
Neutrons were discovered by
n
n
n
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The Nuclear Atom
Nucleus -
Particle Symbol Relative Relative Actual Mass
Charge Mass (amu)
(g)
Electron
9.11 X 10–28
Proton
1.67 X 10–24
Neutron
1.67 X 10–24
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Atomic Number
Atomic Number - is the number of
The elements on the periodic table are organized
In a neutral (uncharged) element, the number of
Mass Number - is the
# of Neutrons =
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Isotopes
Atoms that have the same number of
Most elements have more than one isotope - Hydrogen has
Hydrogen-1 has
Hydrogen-2 has
Hydrogen-3 has
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Complete Isotope Symbols
Y Z
XH
Where X=
Y=
Z=
Hydrogen-1
Chlorine-35
Hydrogen-2
Hydrogen-3
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More Isotope Examples
27Al +3
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Protons
Neutrons
Electrons
127I –1
53
Protons
Neutrons
Electrons
197Au +2
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Protons
Neutrons
Electrons
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Nuclear Stability
The stability of a nucleus depends on its neutron-to-proton
ratio. Elements with atomic #s less than
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Nuclear Stability 2
Nuclei with too many neutrons go through
Just because an atom has gone through radioactive decay does not
mean it is
In addition to the spacing provided by the neutrons, the repulsive
forces of the protons are overcome by the
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Average Atomic Mass
Atomic Mass Unit (AMU) Average Atomic Mass - The atomic mass of an element listed
on the periodic table is a
In order to calculate the average atomic mass of an element
you must know:
1. The
2. The
3. The
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Sample Problem #1
Boron has two naturally occurring isotopes. B-10 has an
atomic mass of
of the naturally
occurring Boron. B-11 has an atomic mass of
What is the
average atomic mass of Boron?
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