Download Atomic Theory - Chemistry

Democritus
-400 B.C.
- Coined the term “atom”
Aristotle
-384-322 B.C.
- Believed matter is
continuous
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1627 – 1690 A.D.
Introduced a scientific approach to chemistry
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All matter is composed of tiny particles
called atoms.
Atoms of the same element have the
same properties. (mass, size, etc.)
In a chemical reaction, matter cannot be
created or destroyed – Law of
Conservation of Mass
Compounds always contain elements in
the same ratio by mass – Law of Definite
Proportions
Dalton
1810
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A penny contains 2.4
x 1022 atoms.
The radius of a single
atom is around
2 x 10-10 m or 0.2 nm.
Scanning tunneling
microscopes can
generate images of
individual atoms.
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Showed electrons are negatively charged
Every atom’s electrons have same charge
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Conclusion: most of an atom is empty space
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Dalton’s Model (1803)
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Rutherford’s Model (1909)
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Thomson’s Model (1897)
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Bohr’s Model (1913)
Electron-cloud
Model (present)
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Robert Millikan
Oil Drop Experiment
Determined charge of
electron
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Max Planck
E=h v
Defined a quantum
of energy
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James Chadwick
Discovered Neutron in 1932
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Nucleus
◦ Contains protons and neutrons
◦ Makes up most of an atom’s mass
◦ Is positively charged
 Proton (+ charge)
 Neutron (0 charge)
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Electron Cloud
◦ Contains electrons
◦ Makes up most of an atom’s volume
Subatomic Charge Location
Particles
Mass
Other
Feature
Proton
+
Nucleus
1 amu
Defines the
element
-Atomic #
Neutron
0
Nucleus
1 amu
Change # to
form isotopes
Electron
-
Electron
Cloud
~0
Atom’s volume
-dictate’s
reactivity
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Short-ranged forces that hold the nuclear
particles together
Between electrically charged particles
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Like charges repel
Opposite charges attract
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Atoms of the same element that differ in
mass
◦ Atomic # = # protons
◦ # protons = # electrons
◦ Mass # = # protons + # neutrons
mass#
atomic#
X
Nuclide
Protons
Neutrons
Protium
1
0
Mass
Number
1
Deuterium
1
1
2
Tritium
1
2
3
108
47
Ag
207
82
80
35
Pb
Br
Silver - 108
Lead - 207
Bromine - 80
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Found in an e- cloud outside of the nucleus
◦ But NOT in paths like the planets
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1st nrg level holds up to 2 e-
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2nd nrg level holds up to 8 e-
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3rd nrg level holds up to 18 e-
2n
2
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Arranged by increasing atomic #
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Rows = Periods
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Columns = Groups OR Families