|
 Dmitri Mendeleev | Russian chemist who discovered a repeating pattern to the elements in 1869, which came to be called the periodic table of the elements |
| Periodic Law | Law that says the repeating properties of elements change periodically as the atomic numbers change |
| Periodic Table | Table that arranges the elements according to their atomic numbers so that elements with similar properties are in the same column |
| Group/ Family | In the Periodic Table, the vertical columns of elements that have similar properties |
| Period | Horizontal row of elements in the Periodic Table listed in order by atomic number which increases from left to right |
| Alkali metals | The elements of Group One on the Periodic Table and are the most reactive, easily forming compounds with other elements |
| Alkaline-earth metals | The elements of Group Two on the Periodic Table that are less reactive than alkali metals |
| Transition metals | The elements of Groups 3 - 12 on the Periodic Table that are less reactive than the other metals |
| Lanthanides | Transition metals from Period 6 that appear in the 1st row under the table; They are typically shiny, reactive metals, some of which are used to make steel. |
| Actinides | Transition metals from Period 7 that appear in the 2nd row under the table; They are typically radioactive and unstable; Those after 94 do not occur in nature |
| Halogens | The very reactive nonmetals in Group 17 that combine readily with other atoms, especially metals |
| Noble gases | The un-reactive nonmetals in group 18 of the Periodic Table |