s block reactions

Reactions of groups 1 and 2

Reactions of groups 1 & 2 (1A, alkali metals, & 2A, alkaline earth metals).	Links
1. Reactions of Group 1 (1A, the alkali metals) with oxygen. All of the alkali metals burn in oxygen with coloured flames. They do not all give the same type of product, however - the one area of group 1 chemistry that is idiosyncratic. Lithium burns with a carmine-red flame to give white lithium oxide: 4Li (s) + O₂ (g) " 2Li₂O (s) Sodium burns with a yellow flame to give pale yellow sodium peroxide. Some sodium oxide is formed as well. 2Na(s) + O₂(g) " Na₂O₂(s) Potassium burns with a lilac flame to give yellow potassium superoxide: K(s) + O₂(g) " KO₂(s) Rubidium and caesium react similarly to potassium to give superoxides; RbO₂ is orange, CsO₂ is red.	Inorganic catalogue contents Group 1 with oxygen Group 1 with water Group 2 with oxygen Group 2 with chlorine Group 2 with water Oxides with water Oxides with acids
2. Reactions of the alkali metals with water. All of the metals react in a similar way. Lithium reacts slowly, melting and rushing about the surface of the water. Sodium reacts vigorously, and may catch fire; potassium reacts violently and always inflames. Rubidium and caesium react extremely violently, and would sink but for the fact they don’t survive for long enough. 2Li(s) + 2H₂O(l) " 2LiOH(aq) + H₂(g)
3. Reactions of Group 2 (2A, the alkaline earth metals) with oxygen. All of the group 2 metals react in a similar way, though barium also forms substantial amounts of barium peroxide BaO₂. Magnesium burns vigorously with a brilliant white flame - the one element in the s-block which does not show its flame test colour (none) when burning. Calcium burns with a brick-red or orange-red flame, strontium with a crimson flame, barium with a pale apple green flame. All of the oxides are white, ionic, basic solids. 2Mg (s) + O₂(g) " 2MgO(s)
4. Reactions of the alkaline earth metals with chlorine. All of the metals react similarly to give white, ionic chlorides. Mg(s) + Cl₂(g) " MgCl₂(s)
5. Reactions of the alkaline earth metals with water. Magnesium reacts very slowly with cold water, but rapidly with steam: Mg(s) + H₂O(g) " MgO(s) + H₂(g) Calcium reacts quite quickly with cold water to give a milky suspension of calcium hydroxide, some of which dissolves. Strontium and barium react similarly, the reaction of barium being vigorous and giving a colourless solution of barium hydroxide – the most soluble of the group 2 hydroxides. Ca(s) + 2H₂O(l) " Ca(OH)₂(aq) + H₂(g)
6. Reactions of group 1 and group 2 oxides with cold water. All of the oxides react to give the hydroxide; peroxides and superoxides give other products as well. Group 1 hydroxides are water-soluble, group 2 oxides are sparingly soluble apart from barium hydroxide which is fairly soluble. Group 1: Li₂O(s) + H₂O(l) " 2LiOH(aq) Na₂O₂(s) + 2H₂O(l) " 2NaOH(aq) + H₂O₂(aq) 2KO₂(s) + H₂O(l) " 2KOH(aq) + H₂O₂(aq) + O₂(g) Group 2: MgO(s) + H₂O(l) " Mg(OH)₂(aq) All the group 2 oxides react similarly; the hydroxides are sparingly soluble and give white suspensions except for barium hydroxide. Calcium oxide reacts very exothermically.
7. Reactions of group 1 and group 2 oxides with dilute acids. All the reactions are shown as ionic equations with H⁺(aq) ions. Group 1: Li₂O(s) + 2H⁺(aq) " 2Li⁺(aq) + H₂O(l) Na₂O₂(s) + 2H⁺(aq) " 2Na⁺(aq) + H₂O₂(aq) 2KO₂(s) + 2H⁺(aq) " 2K⁺(aq) + H₂O₂(aq) + O₂(g) Group 2: MgO(s) + 2H⁺(aq) " Mg²⁺(aq) + H₂O(l) All the group 2 oxides react similarly except with sulphuric acid. In this case magnesium oxide reacts as given, but the sulphates of Ca – Ba are insoluble. The oxide therefore reacts superficially but reaction then ceases.