Unit 1: Atomic Structure
AP Chemistry
Evolution of Atomic Theory
Democritus – 400 B.C.





Greek Philosopher
Imagined particles
that were
indivisible
Constituents of
matter
Atom comes from
“atomos”
Opposed Aristotle
Aristotle – 350 B.C.


Widely accepted
theory that all
matter can be
continually
divided.
Set science back
for thousands of
years.
Alchemy


A pseudoscience that superceded
scientific discoveries.
Alchemists attempted to turn
metals into gold and developing the
“elixir” of life (able to cause
immortality and create life).
Pierre Gassendi - 1650



Reintroduced
Particulate theory
No experimental
evidence
Supported by Sir
Isaac Newton
Robert Boyle - 1661


Studied Gases
1st to use the term
element in its
current context in
his book The
Skeptical Chemist
George Stahl - 1717


Suggested
“phlogiston”
flowed from
burning material
A necessary
ingredient of
combustible
material
Joseph Priestly - 1774

discovered oxygen
supports
combustion
Antoine Lavoisier - 1778


Developed Law of
Conservation of
Mass
Explained
combustion
Joseph Proust - 1799



Developed “Proust’s
Law” using copper
oxide
Later renamed, the
Law of Definite
Proportions
Nearly discovered the
Law of multiple
proportions, but his
data used percentages
instead of weights.
John Dalton - 1802

First to develop an
atomic theory. It
has 4 postulates.


Each element is made
up of atoms
Atoms of the same
element are identical
in mass and
properties. Atoms of
different elements
differ in some way.
John Dalton - 1802


Compounds are made
when atoms combine.
If elements combine
in more than one
whole number ratio,
the resulting
compound has
different properties
Chemical reactions
involve the
reorganization of
atoms.
Amedeo Avogadro - 1811


Developed
Avogadro’s Law.
Equal volumes of
gases have equal
number of
molecules at
constant
temperature and
pressure.
Expanded Dalton’s
concept of atomic
masses
J.J. Berzelius - 1813

Established the 1st
system of using
letters to
represent
elements.
William Prout - 1815

Proposed that
Hydrogen was the
fundamental
material that all
other elements
were made from.
All atomic masses
were multiples of
the mass of
hydrogen.
Michael Faraday - 1833

Found Faraday’s
Constant. 1 mole
of e- = 96500
coulombs.
Alexandre Béguyer de Chancourtois 1862


1st periodic
arrangement of
elements.
Divided surface of
a cylindrical base
into 16 segments
because oxygen
has a mass of 16.
John Newland - 1863

Developed the law
of octaves

Properties of
elements repeat
every eighth
element.
Dimitri Mendeleev - 1869



Classification
based on chemical
properties.
Considered the
first periodic table.
Left gaps for
missing elements
and predicted their
properties
William Crookes - 1879

Showed that
cathode rays
stream from the
negative pole
Eugene Goldstein - 1886

Discovered the proton using a
cathode ray tube.
William Roentgen - 1895


Discovered x-rays.
Rays were
penetrating and of
short wavelength
Henri Becquerel - 1896


Discovered
radioactivity.
Used uranium
salts
Marie Curie - 1897



Student of
Becquerel
Showed that
radioactivity is
atomic property
Isolated radium
and polonium
J.J. Thomson - 1897




Determined the
mass/charge ratio
of the electron.
5.69 x 10-9
Used the cathode
ray tube
Proposed a model
of the atom that
was mockingly
called the “plum
pudding” model
Robert Millikan - 1909



Determined the
charge of the
electron using the
famous oil-drop
experiment
1.60 x 10-19
From this and
Thomson’s value,
the mass was
calculated to be
9.11 x 10-28g
Ernest Rutherford - 1911


Performed the
famous gold foil
experiment
Determined 3
things



The atom is mostly
empty space
The nucleus is
positively charged
The nucleus is a
small dense part of
the atom
Gold Foil Experiment
Gold Foil Experiment
Henry Moseley - 1913

Calculated atomic
number by
determining the
nuclear charge of
an atom.
Niels Bohr - 1913


Observed spectral
lines for hydrogen
Proposed an orbit
theory of the
electron around
the atom.
Bohr Model
Hydrogen Spectrum
Gilbert Lewis - 1916


Suggested that
noble gases have
8 valence
electrons
Atoms will gain or
lose electrons to
achieve 8 outer
electrons.
Louis De broglie - 1924


Suggested that
matter could
exhibit wave
properties
Observed
diffraction patterns
in electrons
Wolfgang Pauli - 1924

Pauli Exclusion
Principle – 2
electrons cannot
have the same 4
quantum numbers
Erwin Schrödinger - 1926


Developed a wave
equation.
Mathematical
function that
described the
nature of the
electron
James Chadwick - 1932

Discovered the
neutron
Other Contributions

C.D. Anderson – 1932


Discovered the positron
Enrico Fermi – 1940

Prepared more than 40 radioactive
elements