Download Atomic Theory

Atoms:
Development of the
Atomic Theory
Democritus

460 BC - Greek philosopher proposes
the existence of the atom

He pounded materials until he made
them into smaller and smaller parts

He called them atoma which is Greek
for “indivisible”.
Democritus

His Theory:
All atoms:
 Are small hard particles

Are made of a single material formed into
different shapes and sizes

Are always moving, and they form
different materials by joining together
John Dalton

1803 - British chemist; elements
combine in specific proportions to form
compounds
Solid Sphere Model or
Bowling Ball Model
Proposed by John Dalton
John Dalton

His Theory:

All substances are made of atoms that
cannot be created, divided, or destroyed.

Atoms join with other atoms to make new
substances.

Atoms of the same element are exactly
alike, and atoms of different elements are
different in mass and size.
J.J. Thomson

1897 - English chemist and physicist;
discovered 1st subatomic particles
Chocolate Chip Cookie
Model or Plum Pudding
Model or Raisin Bun
Model
Proposed by J.J. Thomson
J.J. Thomson

His Theory:

Atoms contain negatively charged
particles called electrons and positively
charged matter.

Created a model to describe the atom as a
sphere filled with positive matter with
negative particles mixed in

Referred to it as the plum pudding model
Ernest Rutherford

1912 - New Zealand physicist
discovered the nucleus
Nuclear Model
Proposed by Ernest
Rutherford
Ernest Rutherford

His Theory:

Small, dense, positively charged particle
present in nucleus called a proton

Electrons travel around the nucleus, but
their exact places cannot be described.
Niels Bohr

1913 - Danish physicist; discovered
energy levels
Bohr Model or Planetary
Model
Proposed by Niels Bohr
Niels Bohr

His Theory:

Electrons travel around the nucleus in
definite paths and fixed distances.

Electrons can jump from one level to a
path in another level.
Erwin Shrodinger

1924 - Austrian physicist; developed
the electron cloud model
Electron Cloud Model
Proposed by Erwin
Schrodinger
Erwin Shrodinger

His Theory:

The exact path of electrons cannot be
predicted.

The region referred to as the electron
cloud, is an area where electrons can
likely be found.
James Chadwick

1932 - English physicist; discovered
neutrons

His Theory:



Neutrons have no electrical charge.
Neutrons have a mass nearly equal to the
mass of a proton.
Unit of measurement for subatomic
particles is the atomic mass unit (amu).
Modern Theory of the Atom

Atoms are composed of three main
subatomic particles: the electron, proton, and
neutron.

Most of the mass of the atom is concentrated
in the nucleus of the atom.
Modern Theory of the Atom

The protons and neutrons are located within
the nucleus, while the electrons exist
outside of the nucleus.

In stable atoms, the number of protons is
equal to the number of electrons.
Modern Theory of the Atom

The type of atom is determined by the
number of protons it has.

The number of protons in an atom is equal to
the atomic number.
Modern Theory of the Atom

The sum of the number of protons and
neutrons in a particular atom is called the
atomic mass.

Valence electrons are the outermost
electrons.