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

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

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

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

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)

Isotope – same number of protons, different number of neutrons

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

Periods go Horizontally Groups go Vertically