Models of the Atom
Scientist and
Time
DEMOCRITUS
400 BCE
JOHN
DALTON
1807
Theory
1. Proposed that all matter
can be divided into
smaller and smaller
particles, called atoms.
2. Proposed that atoms are
of different sizes, in
constant motion, and
separated by empty
spaces.
1. All matter is made up of
atoms.
2. Each element has its own
atoms, with its own
specific mass.
3. Compounds are created
when atoms combine.
4. Atoms cannot be created,
destroyed, or subdivided.
Model
Analogy
Billiard Ball
Model
Models of the Atom
J.J.
THOMPSON
1897
ERNEST
RUTHERFORD
1909
1. Atoms contain particles
known as electrons.
2. Electrons have a small mass
and a negative charge.
3. The rest of the atom is a
positive sphere.
4. The negative electrons are
embedded in this positive
sphere to form a neutral
atom.
1. Performed Gold Foil
Experiment.
2. An atom has a tiny, dense,
core called the nucleus.
3. The nucleus is surrounded by
mostly empty space
containing rapidly moving
electrons.
4. Also discovered the proton
(a positively charged particle
found in the atom’s nucleus)
in 1920.
Plum Pudding
Model
Models of the Atom
NEILS BOHR
1913
1. Electrons move around the
nucleus in circular paths
called orbits.
2. Electrons cannot exist
between orbits, but can ‘jump’
from one orbit to another in
specific quantities.
JAMES
CHADWICK
1932
1. Proposed that an atom must
be empty space with a tiny,
dense central nucleus.
2. This nucleus contains
positively charged protons
and neutral particles called
neutrons.
3. Negatively charged electrons
circle rapidly through the
empty space around the
nucleus.
Planetary Model