-
400 BCE
Democritus
"Atomos" means "not to be cut," which refers to the smallest piece of matter.
Atoms are "uncuttable" -
Period: 300 BCE to
Aristotle
All matter is made up of four
elements: fire, air, water and
earth.
Matter has four properties:
hot, cold, dry, and wet. -
Dalton
Atoms are “uncuttable”.
Atoms of the same element are
exactly alike.
Atoms of different elements
are different. -
Thomson
There are small, negatively
charged particles inside
an atom called electrons.
This theory led to the “plum
pudding” model, in which
negative particles are stuck in a
positively charged substance.
Atoms are made of a single
material that is formed into
different shapes and sizes. -
Rutherford
Atoms contain mostly
empty space.
Electrons are scattered around
the nucleus at a distance.
There is a small, dense,
positively charged nucleus. -
Bohr
Most of an atom’s mass
is in the nucleus.
Electrons travel in paths
called energy levels.
Energy levels are located
certain distances
from the nucleus. -
Modern Cloud Theory
Electrons move around the
nucleus billions of
times in one second.
Electrons’ locations depend
upon how much
energy they have.
Electrons are found in
electron clouds, not in paths.
