| A | B |
|---|
| Actinide | one of the 14 elements with atomic numbers from 90 (thorium, Th) |
| alkali metal | one of the elements of Group 1 of the periodic table |
| alkaline-earth metal | one of the elements of Group 2 of the periodic table |
| anion | a negative ion |
| atomic radius | one-half the distance between the nuclei of identical atoms that are bonded together |
| cation | a positive ion |
| electron affinity | the energy change that occurs when an electron is acquired by a neutral atom |
| electronegativity | a measure of the ability of an atom in a chemical compound to attract electrons |
| halogen | one of the elements of Group 17 |
| ion | an atom or group of bonded atoms that has a positive or negative charge |
| ionization | any process that results in the formation of an ion |
| ionization energy | the energy required to remove one electron from a neutral atom of an element |
| lanthanide | one of the 14 elements with atomic numbers from 58 (cerium, Ce) to 71 (lutetium, Lu) |
| main-group element | an element in the s-block or p-block |
| periodic law | the physical and chemical properties of the elements are periodic functions of their atomic numbers |
| periodic table | an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column, or group |
| transition element | one of the d-block elements that is a metal, with typical metallic properties |
| valence electron | an electron that is available to be lost, gained, or shared in the formation of chemical compounds |
