| A | B |
|---|
| Periodic Table | an arrangement of elements in columns, based on a set of properties that repeat from row to row |
| Period | each row in the table of elements |
| Group | each column in the table of elements |
| Periodic Law | the pattern of repeating properties in the table |
| Atomic Mass Unit (AMU) | one twelfth the mass of a carbon-12 atom |
| Metals | elements that are good conductors of electric current and heat |
| Transition Metals | elements that form a bridge between the elements on the left and right sides of the table |
| Nonmetals | elements that are poor conductors of heat and electric current |
| Metalloids | elements with properties that fall between those of metals and nonmetals |
| Valence Electron | an electron that is in the highest occupies energy of an atom |
| Alkali Metals | metals that have a single valence electron and are extremely reactive - group 1A |
| Alkaline Earth Metals | metals that have two valence electrons - group 2A |
| Halogens | elements that have seven valence electrons - group 7A |
| Noble Gases | elements that have eights valence electrons with the exception of Helium which has two valence electrons - group 8A |
