| A | B |
|---|
| proton | positively charged subatomic particle; determines identity of atom and contributes to atomic mass |
| neutron | neutrally charged subatomic particle; affects the stability of the nucleus and contributes to atomic mass |
| electron | negatively charged subatomic particle; involved in chemical reactions |
| ion | a charged atom or chemically bonded group of atoms; may be negative or positive |
| isotope | an atom of a element with a particular number of neutrons leading to a particular atomic mass; any element may have several isotopes |
| alpha particle | a helium nucleus emitted during radioactive decay |
| beta particle | an electron emitted during radioactive decay |
| gamma rays | electromagnetic radiation emitted during radioactive decay |
| alkali metals | group 1 metals; the most reactive metals |
| alkaline earth metals | group 2 metals; fairly reactive metals |
| halogens | group 17 nonmetals; the most reactive nonmetals |
| noble gases | group 18 nonmetals; nonreactive elements |
| groups or families | the columns on the periodic table |
| periods | the rows on the periodic table |
