Download History of Atom

~450BC
Who was the first to propose that matter was
made of tiny indivisible particles ?
Democritus’s atom
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matter was made up of tiny invisible
indivisible particles in constant motion
surrounded by an empty space (void)
solid (no void inside)
eternal (indestructible)
Differ from one another in shape, size,
arrangement
Aristotle
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Disapproved of Democritus’ idea of atoms
Believed that all matter was comprised of
Earth, wind, fire and water
Dalton’s Atom
The Atom – Circa 1800
indivisible
1st Modern Atomic Theory
1.
2.
3.
4.
Matter consists of tiny particles called
atoms.
Atoms of one element are alike and
are different from atoms of another
element.
Atoms are indestructible and
unchangeable (law conservation of
matter). Lavoisier
Atoms combine in simple whole number
ratios to form compounds (law of
definite proportion).Lavoisier
Lavoisier (early 1700’s)
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Father of modern
chemistry
Law of conservation of
matter –
matter not
created not destroyed
Faraday 1839
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Electrolysis experiments
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Structure of atoms related
to electricity
Charge is somehow involved
in binding elements together
to form compounds
Crooke’s tube/Cathode Ray tube
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2 electrodes
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Cathode: negatively charged electrode
Anode: positively charged electrode
Rays from cathode to anode
Deflection of a charged particle
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1.
2.
3.
4.
5.
mass
velocity
charge of the particle
Strength of magnet
amount of charge on the plates
JJ Thomson
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Experiments with cathode
ray tube:
Conclusion:
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Cathode ray was a stream of
negatively charged particles
called electrons
Later protons were found
going in an opposite direction
Plum Pudding Model
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Sphere of positive charge
with electrons embedded in it.
Millikan’s Oil Drop Experiment 1909
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Determined charge of
electron using
Thomson’s charge to
mass ratio
Charge = 1.6 X 10-19C
Roentgen
1870’s
cathode ray tube gave off
X-rays
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Becquerel
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Discovers
radioactivity(spontane
ous emission of
particles or rays)
when photographic
film becomes exposed
in the presence of a
sample of uranium
Refers to Pierre and
Marie Curie
Marie and Pierre Curie (1900’s)
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Discovered Radium
(Ra) and Polonium (Po).
Marie won 2 Nobel
prizes
Marie died of cancer
and Pierre was killed
by a horse drawn milk
truck
Daughter Irene
continued their work
Rutherford 1909
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Lead Box Experiment
3 types of radiation from
radioactive substances: α, β, γ
Gold foil experiment
 Positively charged alpha
particles (He nucleus) were shot
at a thin piece of gold foil
 Expected α particles to go right
through
Gold Foil Experiment
Rutherford’s Conclusion
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-Atom mostly empty space
-Positive charge and mass
concentrated in tiny dense
-nucleus
The neutron
Chadwick – 1932
• Neutral radiation by nuclear
bombardment nuclear reaction
• No charge but same mass as
proton
Neutral Carbon-12 atom
Subatomic particles
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Proton
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Neutron
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Inside nucleus
+1
1 amu
Inside nucleus
0
1amu
Electron
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Outside nucleus
-1
O amu(1/2000amu)
Don’t get confused
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Atomic number
number of protons
(on periodic table- top)
Mass Number
number of protons plus neutrons
(not on periodic table)
Atomic Mass
the weighted average of the mass
numbers for all the
isotopes of the atom
(on periodic table – bottom)
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Symbols
Name-mass number
charge
Mass
number
Atomic
number
X
Atoms
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Protons=electrons
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Atoms have no charge
ISOTOPES
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Atoms with the same number of protons but a
different number of neutrons.
Examples
3
Hydrogen-3
Hydrogen-2
Hydrogen-1
H
1
2
H
1
1
1
1
H
Ions
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Atoms that gain or lose electrons and
become charged
Charge= protons- electrons
Practice with ions
1. Write the symbol for calcium+2-41
How many protons, electron, neutrons
2. Write the symbol for oxygen-2-18.
How many protons, electron, neutrons?
Atomic Mass
Make table:
Mass
X
Abundance
=
Atomic Mass= __________
Atomic Mass
Make table:
Mass
X
Cu-63
Cu-65
Abundance
69.1%
=
30.9%
=
= ________
+_________
Atomic Mass= __________
Atomic mass
Element X has 2 isotopes X-10 and
X-11. If the atomic mass is 10.8,
what is the abundance of each?
Pennies
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Pre 1982 – mostly copper
penny cost more than a penny to make
Except in 1943 pennies were zinc coated
steel – “steel pennies”
Post 1982 – 97% zinc coated with copper
since zinc is less expensive than copper
What image did the early Greeks have
of atoms?
Further developments
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Moseley: found elements contain a unique
positive charge
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Number of protons in nucleus is what
determines the identity of the element
Periodic table arranged according to atomic
number
Chadwick (1930’s)
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Discovers neutron
Practice
1.
2.
Write the symbol for sodium-24
How many protons, electron
and neutrons?
Write the symbol for Tin-123
How many protons, electron
and neutrons?
Proust 1799
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Law of constant composition
(law of definite proportions)
Observed that a compound
always contained the same
elements in the same
proportion by mass
example: water is always
88.9% oxygen and 11.1%
hydrogen by mass
Calculate the atomic masses
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Copper-63
Copper-65
69.1%
30.9%
Uranium-234
Uranium-235
Uranium-238
.001%
.71%
99.23%