1. II. Subatomic Particles

2. Recall – History of the Atom
Democritus
Developed idea of atoms
Called smallest bit of matter “atomos” meaning indivisible
John Dalton
Believed matter consisted of lumpy particles (atoms)
“Billiard Ball Model” – did not know structure; thought atoms were hard spheres.

3. Recall – History of the Atom Cont.
J. J. Thompson
Discovered the electron
Knew electrons had negative charge
Based off of experimentation with cathode ray tube
Developed “plum pudding model”
Believed negative electrons existed in a positive “pudding”
Think chocolate chips in a chocolate chip cookie

5. Recall – History of the Atom Cont.
Ernest Rutherford
Discovered the nucleus through gold-foil experiment
Discovered nucleus consisted of positively charged particles; named them protons

6. Recall – History of the Atom Cont.
Niels Bohr
Rules
Electrons can only orbit at certain allowed distances
Atoms radiate Energy when electrons jump from higher-energy orbital to lower-energy orbital
Electron can exist in only one of the orbits at any one time

7. A. The Atom and Subatomic Particles
Atom – Smallest particle of an element that retains the properties of the element
Atoms are composed of 3 things
Electrons (e–)
Protons (p+)
Neutrons (no)

9. III. How Atoms Differ

10. What makes an atom of one element different from an atom of another element?
The number of protons

11. A. Atomic Number Atomic Number Chemical Symbol Chemical Name
Average Atomic Mass

12. Atomic Number = number of protons
A. Atomic Number Cont.
Atomic Number
= number of protons
= number of electrons (in a neutral atom)
Atomic Number
Chemical Symbol
Chemical Name
Average Atomic Mass

13. 82 82 O 8 8 Zn 30 30