Transcript Atomic Theory

The History of the
Atomic Theory
Democritus
• 300 BC
• Atom the indivisible; cannot be further
broken down into smaller pieces".
• The atom as the smallest particle of
matter.
Dalton
c.1800
- Atoms are seen as solid, indestructible
spheres (like billiard balls)
- Explains how atoms combine
to form molecules.
- Confirms basic Laws of Chemistry:
“Conservation of Mass and
Definite Proportions”.
JJ Thomson
• C. 1850
• Chocolate chip cookie model :
• Atoms are solid spheres made-up of a
solid positive mass (or core) with tiny
negative particles embedded in the
positive core.
Rutherford
• 1905
• Famous Gold Leaf Experiment.
• Proved the atom is mostly made of empty
space.
• Proved that the nucleus is
positive and the electrons are
outside the nucleus.
Bohr
• 1920
• Electrons in definite energy levels
around the nucleus.
• Proved that electrons are placed in
definite energy levels (called Orbitals)
around the nucleus.
• Speaks of Neutrons in the nucleus
* 2, 8, 8, 2 *
Atomic Review Video
Main Principles:
- All matter is made up of tiny particles called
atoms.
- Atoms are made of even smaller particles:
Protons (+), Electrons (-), and Neutrons (o)
- Atoms can be distinguished from each
other by their number of protons, electrons
and neutrons.
Periodic Table of Elements
What the heck does it mean?
Each element is broken down the same way.