The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) are the second most reactive metals in the periodic table, and, like the Group 1 metals, have increasing reactivity in the higher periods. Beryllium (Be) is the only alkaline earth metal that does not react with water or steam, even if metal is heated to red heat. Additionally, beryllium has a resistant outer oxide layer that lowers its reactivity at lower temperatures.
Magnesium shows insignificant reaction with water, but burns vigorously with steam or water vapor to produce white magnesium oxide and hydrogen gas:
-
Mg(s) + 2 H2O(l) ⟶ Mg(OH)2(s) + H2(g)
A metal reacting with cold water will produce metal hydroxide. However, if a metal reacts with steam, like magnesium, metal oxide is produced as a result of metal hydroxides splitting upon heating.
The hydroxides of calcium, strontium and barium are only slightly water-soluble but produce sufficient hydroxide ions to make the environment basic, giving a general equation of:
-
M(s) + 2 H2O(l) ⟶ M(OH)2(aq) + H2(g)
| Order of reactivity |
Metal |
Reactions with water or steam |
| most reactive |
potassium (K) |
very vigorous reaction with cold water |
| ↑ |
sodium (Na) |
vigorous reaction with cold water |
| ↓ |
calcium (Ca) |
less vigorous reaction with cold water |
| least reactive |
magnesium (Mg) |
slow reaction with cold water, vigorous with steam |
- If metals react with cold water, hydroxides are produced.
- Metals that react with steam form oxides.
- Hydrogen is always produced when a metal reacts with cold water or steam.