Group 2 & Group 17

Group 2 — the alkaline earth metals

Going down Group 2 (Be → Ba): atoms get larger, ionisation energies fall, and reactivity increases (electrons more easily lost). They react with water to form hydroxides and hydrogen:

$$\text{Ca} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2$$

Solubility of hydroxides $\text{M(OH)}_2$ increases down the group ($\text{Mg(OH)}_2$ sparingly soluble, $\text{Ba(OH)}_2$ soluble) → alkalinity increases down.
Solubility of sulfates $\text{MSO}_4$ decreases down the group ($\text{BaSO}_4$ insoluble — the basis of the sulfate test with $\text{Ba}^{2+}$).