| A | B |
|---|
| atomic mass | mass of one atom of an element |
| atomic number | number or protons in the nucleus of one atom of an element |
| electron | negatively charged particle outside the nucleus of an atom |
| group | column of elements in the periodic table that are similar |
| neutron | particle inside the nucleus of an atom that has a neutral (no) charge |
| period | a row of elements in the periodic table in number order |
| proton | positively charged particle in the nucleus of an atom |
| periodic table | a listing of all known elements |
| halogens | group of elements that are highly reactive nonmetals |
| nobel gases | group of elements that generally do not react with other elements |
