ElementsWhat are the alkali metals?
The alkali metals fill the first column of the table, below hydrogen. They are soft enough to cut with a knife, shiny when freshly cut, and light. Each atom has one outer electron that it gives up very easily, which makes these the most reactive metals. All of them react with water to give hydrogen gas and an alkali, and the reaction gets more violent going down the column. For this reason they are never found pure in nature and are stored under oil. Their compounds, such as common salt, are among the most familiar chemicals.
The family in numbers
Melting points in this family run from 26.9 °C (francium) to 180.5 °C (lithium). Among its solid members, the least dense is lithium (0.53 g/cm³) and the densest is caesium (1.93 g/cm³). The most recently discovered member is francium (1939).
All alkali metals compared
| No. | Symbol | Name | Atomic mass | State | Melts at | Boils at | Density g/cm³ | Discovered |
|---|---|---|---|---|---|---|---|---|
| 3 | Li | Lithium | 7.0 | Solid | 180.5 °C | 1,342 °C | 0.53 | 1817 |
| 11 | Na | Sodium | 22.9897693 | Solid | 97.8 °C | 882.9 °C | 0.97 | 1807 |
| 19 | K | Potassium | 39.0983 | Solid | 63.4 °C | 758.9 °C | 0.89 | 1807 |
| 37 | Rb | Rubidium | 85.468 | Solid | 39.3 °C | 687.9 °C | 1.53 | 1861 |
| 55 | Cs | Caesium | 132.9054520 | Solid | 28.4 °C | 670.9 °C | 1.93 | 1860 |
| 87 | Fr | Francium | 223.01973 | Solid | 26.9 °C | no value | no value | 1939 |
Other families: alkaline earth metals, transition metals, post-transition metals, metalloids, nonmetals, halogens, noble gases, lanthanides, actinides.