1. 3.3 The Atom

2. Periodic Table of Elements Atomic Number: Number of protons in an atom; usually appears directly above the chemical symbol. Number of protons in an element is usually balanced by an equal number of electrons (negatively charged particles).

3. Atomic Mass : Average masses of all the isotopes Mass Number: Number of protons plus neutrons in an atom; usually appears directly below the chemical symbol. Periodic Table of Elements

4. Atom Equations Atomic Number:# of Protons = # of Electrons Atomic Weight:# of Protons + # of Neutrons # of Neutrons:Atomic Weight - # of Protons # of Protons:Atomic Weight - # of Neutrons

5. Ions Ions: Have the same atomic number and the same mass number, but have a different charge because of a different number of electrons

7. Isotopes Isotopes: Have the same atomic # but different mass numbers because of a different number of neutrons.

8. Compounds Pure substances made up of two or more elements. Physical and chemical properties of elements change when they bond with others substances. Physical and chemical properties of elements change when they bond with others substances. Molecule: the smallest part of a compound that still has all of the properties of that compound. Molecule: the smallest part of a compound that still has all of the properties of that compound.