• Discovered electrons through experiment cathode ray and showed it in the plum pudding model

• Gold Foiled experiment
• Discovered nucleus has a positive charge and electons surrounding nuclus is just empty space

Bohr

• Combined other experiments and used knowledge .
• Discovered electrons move in a fixed orbit around the nucleus.
• Further away from nucleus--> higher energy level
• To gain or lose E, you move to different energy levels

• Nucleus = small proportion of atom containing P & N
• Empty spaces around nucleus w/ electrons = E cloud
• Position & velocity of E cannot be percisely calculated. Can only be shown in an area of high probability known as the electron shell.
• Lowest energy levels must be filled before electrons can move to any other level.

1. All matter is made of atoms. Atoms are indivisible and indestructible.
2. All atoms of a given element are identical in mass and properties

3. Compounds are formed by a combination of two or more different kinds of atoms.

4. A chemical reaction is a rearrangement of atoms.

• One of two or more forms of a single element; the atoms of each isotope have the same number of protons but different numbers of neutrons in their nuclei. Thus isotopes have the same atomic number but differ in atomic mass

Force that is he key to the power of the sun; responcible for a process known as radioactive decay

force acts between all mass in the universe and it has infinite range.