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

D. 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 ***Inside shells fill first

E. Atoms are mostly empty space (Rutherford, 1871) 99% of particles 1% of particles

F. Atoms can be electrically charged 1. If protons = electrons neutral atom 2.Protons do not = electrons ion (charged atom)

G. 117 Different Types of Atoms (92 naturally occurring and 5 are common to life: C.H.O.N.S.) 1. Identified by the number of protons Hydrogen: 1 Helium: 2 Oxygen: 8 2. Element – atoms with the same number of protons a. Pure; cannot be broken down (ex. Gold) 3. 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