3.1.2
Redox reactions and reactivity of group 2 elements
(a)→all elements in group 2 [alkali metals] jabe 2 outer e- in s subshell [s2]
→alkali metals are usually oxidised in redox reactions: losing 2e- to form 2+ ions
(b)(i)→reactivity increases down Group 2: larger atomic radi and more shielding so less nuclear attraction and easier to remove outer e-
→group 2 metals with oxygen forms metal oxides: 2M (s) + O2 (g) → 2MO (s) ; this is a redox reaction as M= 0→+2 [oxidised] and O= 0 →-2 [reduced]
(ii)→group 2 metals with water forms metal hydroxides and H2: M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g) ; this is a redox reaction as M= 0→+2 [oxidised] and H= +1→0 [reduced]
(iii)→group 2 metals with dilute acids forms salts and H2: e.g. M (s) + 2HCl (aq) → MCl2 (aq) + H2 (g) or M (s) + H2SO4 (aq) → MSO4 (aq) + H2 (g)
(c)→formation of 2+ ions in group 2 elements require 2 ionisation energies: M(g) → M+(g) + e- then M+(g) → M2+(g) + e-
→both ionisation energies decrease down the group as: less attraction between nucleus and outer e- and increased atomic radi and shielding
Reactions of Group 2 compounds
(d)→group 2 are more alkali down the group: due to increasing solubility meaning solutions formed contain more hydroxide ions [more concentrated] e.g. Mg[OH]2 has ph 10 but Ba[OH]2 ph13
(e)(i)→calcium hydroxide in agriculture: used to neutralise acidic soils Ca(OH)2 (s) + 2H+ (aq) → Ca2+ (aq) + 2H2O (l)
(ii)→magnesium hydroxide in medicine: ysed to neutralise excess stomach acid to treat constipation Mg(OH)2 (s) + 2HCl (aq) → MgCl2 (aq) + 2H2O (l)