1. Intro to Chemistry Atoms Smallest whole particle of matter
Parts of an atom (subatomic particles)
1. Protons: + charge
Nucleus (99% of atom mass)
2. Neutrons: neutral
3. Electrons (electron cloud): - charge (2000X smaller)
Diagrams

2. Electrons orbit in different energy levels called “shells”
1. Like lanes of a race track
2. Each shell holds a limited number of electrons N
Max e-
Shell M K 2 L K L 8 M 18 N 32
***First two shells fill first

3. Atoms are mostly empty space (Rutherford, 1871-1937)
He shot alpha particles through gold foil and 99% of the particles when right through.

4. Atoms can be electrically charged
If protons = electrons neutral atom
ion (charged atom)
Protons do not = electrons
Losing electrons creates a positive atom
Gaining electrons creates a negative atom

5. 118 Different Types of Atoms 92 naturally occurring
5 are common to life: C.H.O.N.S.
Atoms are identified by the number of protons
Elements – Atoms with the same number of Protons
Hydrogen: 1
Helium: 2
Oxygen: 8
a. Pure; cannot be broken down (ex. Gold)

6. Isotope – same number of protons, different number of neutrons

7. H. All Elements are Organized on a Periodic Table
I. The symbol and other info about the element is in each box
Atomic Number - # of protons
Atomic Symbol
Atomic Mass – Protons + Neutrons

8. Periods go Horizontally Groups go Vertically