Discuss the trend of the following
(i) Thermal stability of carbonates of Group 2 elements.

(ii) The solubility and the nature fo oxides of group 2 elements.

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Solution

Carbonates of metal: Thermal stability

The carbonates of alkali metals except lithium carbonate are stable to heat. The carbonates of group-2 metals and that of lithium decompose on heating, forming an oxide and carbon dioxide. For example,

$L i_{2} C O_{3} + H e a t \to L i O + C O_{2} M g C O_{3} + H e a t \to M g O + C O_{2} N a 2 C O 3 + H e a t \to n o e f f e c t$

The stabilities of carbonates of alkaline earth metals increase on moving down the group.

For example, $B e C O_{3}$ decompose at 373 K, $M g C O_{3}$ at 813 K, $C a C O_{3}$ at 1173 K, $S r C O_{3}$ at 1563 K.

$B e C O_{3} < M g C O_{3} < C a C O_{3} < S r C O_{3} < B a C O_{3}$
$B e C O_{3}$ is unstable to the extent that it is stable only in atmosphere of $C O_{2}$ These carbonates however show reversible decomposition in closed container.
$B e C O_{3} ⇌ B e O + C O_{2}$

solubilities in water:

carbonates of alkali metals, except $L i_{2} C O_{3}$ , are soluble in water. Their solubilities increase on moving down the group. Carbonates of group-2 metals are almost insoluble in water and their solubilities further decrease on moving down the group. In fact, these metals can precipitate from their salt solutions as carbonates.

Nitrates of metal: Thermal stability Nitrates of alkali metals, except $L i N O_{3}$ , decompose on strong heating forming nitrites and oxygen.

for example, $2 K N O_{3} \to 2 K N O_{2} + O_{2}$

Nitrates of alkaline-earth metals and $L i N O_{3}$ decompose on heating to form oxides, nitrogen to form oxides, nitrogen dioxide, and oxygen.

$4 L i N O_{3} + H e a t \to 2 L i_{2} O + 4 N O_{2} + O_{2} 2 C a (N O_{3})_{2} + H e a t \to 2 C a O + 4 N O_{2} + O_{2}$

Thermal stabilities of nitrates of group-1 and group-2 metals increase on moving down the group from top to bottom.

solubility: Nitrates of group -1 and group-2 metals are all soluble in water. The solubilities of these salts further increase on descending the group.

Sulphates of metal: Thermal stability The sulphates of group-1 and group-2 metals are all thermally stable.

solubility: sulphates of alkali metals are soluble in water. The sulphate of alkaline earth metals is less soluble. Their solubilities decrease on moving down the group from Be to Ba.

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Similar questions

Present a comparative account of the alkali and alkaline earth metals with respect to the following charactieristics.

(i) Tendency to form ionic / covalent compounds

(ii) Nature fo oxides and their solubility in water

(iii) Formation of oxosalts

(iv) Solubility of oxosalts.

(v) Thermal stability of oxosalts.

Based on the group valency of elements state the formula for the following giving justification for each:

(i) Oxides of 1st group elements.

(ii) Halides of the elements of group 13.

(iii) Compounds formed when an element of group 2 combines with an element of group 16.

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