History of Chemistry Discoveries and Atoms
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Transcript History of Chemistry Discoveries and Atoms
History of
Chemistry
Discoveries and Atoms
Early Greeks
Democritus – all matter is made of
small, indivisible particles called
“atomos”
Aristotle – matter is continuous and
NOT made of smaller particles
Robert
1st
Boyle (1600’s)
true “chemist”
Discovered
a relationship
between pressure and
volume (Boyle’s Law)
Antoine
Lavoisier
Matter
cannot be created
or destroyed
Law of Conservation of
Mass
Joseph
Proust
Found
that a given compound
always contains exactly the
same proportion of elements
by mass
Law of Definite Proportions
John
Dalton (1800’s)
The
ratios of the masses of
elements in a compound can
always be reduced to small
whole numbers
Law of Multiple Proportions
Dalton’s Atomic Theory
1) all matter is composed of tiny particles
called atoms
2) the atoms of an element are always
identical while the atoms of different
elements are different
3) compounds form when atoms
combine; atoms combine in small whole
number ratios
4) reactions involve reorganization of
atoms; the atoms themselves do not
change
Dalton
Proposed
the “Billiard-ball
model” of the atom
Joseph
Gay-Lussac (1809)
Measured
the volumes of
gases that reacted with one
another to develop the
Law of Combining Volumes of
Gases
Amadeo
Avogadro
at the same temperature and
pressure, equal volumes of
gases contain the same
number of particles
Avogadro’s hypothesis
J.J.
Thomson
Produced
a “cathode ray”
which was deflected by a
negative electric field
Thus
the ray must be made of
negative particles (electrons)
J.J.
Thomson
Since
atoms are neutral, they
must also have a positive area
Plum
pudding model
J.J.
Thomson
Protons
were found to be
1836 X the mass of an
electron
Charge of proton is +1
Robert
Millikan
Oil
drop experiment to
determine the magnitude of
the electron’s charge
which is now known as -1
James
Chadwick
Discovered
high energy
particles with no charge
and the same mass as the
proton –
the neutron
Henri
Becquerel
Accidentally
discovered
radioactivity
Alpha particles (+2 charge)
(Also beta particles, gamma
rays)
Ernest
Rutherford (1911)
Tests
Thomson’s Plum Pudding
Model by shooting alpha
particles through a sheet of gold
foil
Ernest
Rutherford
Nuclear Model
of the Atom
Robert
Bunsen
Found
that when heated,
different elements produced
different colors in a flame
Niels
Bohr (1912)
Electrons “orbit” the nucleus
somewhat like planets orbit the sun
Planetary Model
Arnold
Sommerfeld
Expanded the Bohr model
Electrons travel in orbitals, but
the orbitals are not the same shape
-- this leads to the electron cloud
model of the atom
Electron Cloud Model
Wolfgang
Pauli (1924)
Predicted
that electrons spin
while orbiting the nucleus
Pauli’s Exclusion Principle says
no two electrons do the exact
same thing at the same time
de Broglie and Schrödinger
Propose
that electrons move
like wave
thus the Wave-Mechanical
Model
Werner
No
Heisenberg
experiment can measure
the position and momentum
of a quantum particle
simultaneously
Heisenberg’s Uncertainty
Principle
Modern View of the Atom
Tiny
nucleus surrounded by
electron “cloud”
Nucleus accounts for all of the
mass
Arrangement of electrons causes
different chemical properties
Electron Cloud Model
Note: Just as no map can equal a territory,
no concept of an atom can possibly equal
its nature. These models of the atom
simply served as a way of thinking about
them, though they contained limitations
(all models do).