1. HISTORY OF THE ATOM AND ATOMIC THEORY

2. ATOMS
The smallest part of an element that retains the properties of that element

3. Came up with the word “atom”
DEMOCRITUS
Greek philosopher
Came up with the word “atom”
Thought atoms were indivisible (couldn’t be broken down any further)

4. JOHN DALTON All atoms of an element are exactly alike.
Atoms of different elements combine to form compounds.
Law of Definite Proportions - those compounds always contain elements in the exact same proportions
Ex.; water is always H2O

5. JJ Thomson
Discovered atoms were NOT indivisible… they could be divided into smaller parts
Discovered electrons – negatively charged particles within the atom
Plum-Pudding Model – said the electrons were spread throughout the atom

6. ERNEST RUTHERFORD
Gold foil experiment – helped revise Thomson’s Plum-Pudding model
positively charged particles aimed at a thin sheet of gold foil.
thought most particles would travel straight through the foil, a few would be slightly deflected.
most went through, but some were deflected by a large amount
this indicated there was a positive charge in the center of the atom, and the center was small compared to the size of the atom

7. GOLD-FOIL EXPERIMENT

8. RUTHERFORD’S MODEL OF THE ATOM
Nucleus – center of the atom containing protons (positively charged) and neutrons (no charge)
Electrons – negatively charged particles that orbit around the nucleus

9. NIELS BOHR
Suggested electrons are in certain energy levels surrounding the nucleus and they gain energy to move to higher levels or lose energy to move to lower levels

10. MODERN ATOMIC THEORY
Nucleus of an atom is small, dense & in the center with protons and neutrons.
Electrons don’t occupy energy levels
Electrons behave more like waves than particles
It’s impossible to pinpoint the exact location of an electron
Orbital – region of space around the nucleus where an electron is likely to be