| A | B |
|---|
| Period | a row in a periodic table elements; the time required for one complete cycle of a periodic motion |
| Group | a column of elements in a periodic table |
| Periodic Law | the pattern of repeating properties displayed by elements in the periodic table |
| Atomic mass unit (amu) | one twelfth the mass of a carbon-12 atom |
| metals | elements that are good conductors of heat and electric currents |
| transition metals | elements that form a bridge between elements on the left and right sides of the periodidc table |
| nonmetals | elements that are poor conductors of heat and electric current |
| metalloids | elements with properties that fall between those of metal and nonmetals |
| Valence electron | an electron that is in the highest occupied energy level of an atom |
| alkali earth metals | the elements in Group 2A of the periodic table |
| halogens | the elements in Group 7A of the periodic table |
| noble gases | the elements in Group 8A of the periodic table |
