1. Alkali metals
Group I elements are called alkali metals, which include lithium, sodium and potassium, and other metals in group I.
Alkali metals are metals, and they will show most typical properties of metals. Beside these, alkali metals show some special physical properties:
- soft
- low melting points (decreasing mp down the group)
- low density (increasing density down the group)
| metal | density g/cm3 | melting point ℃ | boiling point ℃ | hardness |
| lithium | 0.53 | 181 | 1342 | fairly soft |
| sodium | 0.97 | 98 | 883 | soft |
| potassium | 0.86* | 63 | 760 | very soft |
2. Chemical properties of alkali metals
Alkali metals are the most reactive metals because only one electron will be lost for them to form a stable electronic structure. All of them can react with water to produce an alkaline solution and hydrogen gas.
alkali metal + water → hydroxide + hydrogen
2M + 2H2O → 2MOH + H2
M can represent any alkali metals, such as
2Na + 2H2O → 2NaOH + H2
Down the group, the reactivity increases due to easier to lose electron at outermost shell.
| metal | gas production | heat produced by reaction | production of alkaline solution | production of flame |
| lithium | fizzes slowly, a few bubbles | moves slowly on the surface, does not melt | metal disappears slowly, solution turn purple | no flame |
| sodium | fizzes strongly, many bubbles | melts into a ball on surface and moves about | metal disappears quickly, solution turns purple | no flame unless held in place |
| potassium | fizzes violently, very many bubbles | melts and moves very quickly on surface | disappears very quickly, solution turns purple | hydrogen ignites, a lilac flame produced |
Due to increasing reactivity down the group, rubidium and caesium will be more reactive when they react with water.
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