| A | B |
|---|
| nucleus | The center of an atom |
| proton | positively charged particle in nucleus |
| electron | negatively charged particle outside the nucleus |
| neutron | particle in nucleus with no charge |
| atomic number | number of protons an atom of an element |
| mass number | mass of an atoms protons + neutrons |
| isotopes | atoms of same element with different number of neutrons |
| periodic table | arrangement of elements based on properties |
| period | row on the periodic table |
| group | column on the periodic table |
| family | column on the periodic table |
| periodic law | Elements in groups have similar properties |
| atomic mass unit | mass of 1 proton or 1 neutron |
| metals | malleable, ductile elements with good conductivity |
| transition metals | elements in groups 3-12 |
| nonmetals | Non-malleable elements that are poor conductors |
| metalloids | elements with properties of metals and nonmetals |
| valence electrons | electrons in the highest energy level |
| alkali metals | highly reactive elements in group 1 |
| alkaline earth metals | Group 2 metals. Have 2 valence electrons |
| halogens | group 7A highly reactive nonmetals |
| noble gases | group 8A colorless, odorless, unreactive gases |
