1. Atoms!
What is matter made of?

2. A Quick Pre-Test Answer these in your notes: What are atoms made of?
What is the estimated size of atoms?
Draw a picture of a simple atom on your paper.

3. From the beginning…
Democritus, Greece 4th century BC, suggested the existence of the “atom”

4. John Dalton (1766-1844) English schoolteacher
Created the atomic theory

5. Dalton’s Atomic Theory
Elements are made of very small particles called atoms.
Atoms of the same element are identical.
Atoms can’t be subdivided, created, or destroyed.
Atoms of different elements combine in simple, whole-number ratios to form compounds.
In chemical reactions, atoms are combined, separated or rearranged.

6. How small is an atom? Consider the following…
A penny contains about 2.4 x 1022 atoms, while the world has about 7.6 x 109 people.

7. More tiny than atoms There are 3 subatomic particles: Electrons
Protons
Neutrons

8. Protons Positively charged subatomic particles
Discovered in by Goldstein
Charge = +1
Mass = 1amu (actual=1.67x10-24g)

9. Electrons Negatively charged subatomic particle
Discovered by JJ Thomson in 1897
Millikan discovered the charge on an e- to be -1
Mass of an electron = 1/1840 of a proton (9.11x10-28g)

10. Atomic Nucleus Discovered by Rutherford (1911)
Nucleus: dense central core of the atom that contains protons and neutrons

11. Neutrons Subatomic particles with no charge
Discovered by Chadwick in 1932
Mass is equal to proton

12. In summary… PROTON ELECTRON NEUTRON CHARGE +1 -1 MASS 1 amu ~0
MASS
1 amu ~0
LOCATION
nucleus
Outside the nucleus
Nucleus