| A | B |
|---|
| Periodic | Having a regular, repeating pattern. |
| Periodic Law | The law that states that the chemical and physical properties of elements are periodic functions of their atomic numbers |
| Period | A horizontal row of elements on the periodic table. |
| Group | A column of elements on the periodic table. |
| Alkali Metals | The elements in Group 1 of the periodic table; they are the most reactive metals, and their atoms have one electron in their outer level. |
| Alaline-earth metals | the elements in Group 2 of the periodic table; they are reactive metals but less reactive than alkali metals; their atoms have two electrons in their outer level. |
| Halogens | the elements in Group 17 of the periodic table; they are very reactive nonmetals, and their atoms have seven electrons in their outer level |
| noble gases | the unreactive elements in Group 18 of the periodic table; their atoms have eithg electrons in their outer level (full valence levels), except for Helium, which is full with two valence electrons |
