Download The Atomic Theory

What is the Atomic Theory?
•
•
Democritus
Dalton
•
440 B.C.
– Thought matter was made of tiny
particles
– Believed these particles could not be
cut into anything smaller pieces
– Called these particles atoms, which
means not able to be divided
•
British scientist, 1700’s
– Thought atoms were small solid spheres
like a marble
•
Came up with the atomic theory in
1803
– All substances are made of atoms.
Atoms cannot be created, divided or
destroyed
– Atoms of the same element are exactly
alike, and atoms of different elements
are different
– Atoms join with other atoms to make
new substances
• J.J. Thomson
• 1897 – Made a correction to Dalton’s
theory
– Discovered that atoms contained negatively
charged particles he called electrons
– Developed the plum pudding model to show
what he thought an atom looked like
– Electrons were located throughout the
entire atom
• Rutherford
• 1911 – Revised the atomic theory
– Gold Foil experiment
– Discovered that atoms have a dense center
which he called a nucleus
– This center contained positively charged
particles he called protons
– Electrons surrounded the nucleus with large
amounts of space between the nucleus and
the electrons
• Bohr
• 1913 – Proposed that electrons
moved around the nucleus in
certain pathways
– Known as the solar system model
• Electron Cloud Model
• Electron Cloud Model
– Center of atom is very small and
very dense, nucleus
– In the nucleus are positively charge
particles called protons and
neutron, particles with no charge
– Electrons move around the nucleus
in orbits.
– These orbits do not have any set
pathways
– Because the electrons move so
fast, they create the illusion of a
cloud