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The S-Block Elements

Question
CBSEENCH11008360
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Property of the alkaline earth metals that increases with their atomic number

  • the solubility of their hydroxides in water

  • the solubility of their sulphates in water

  • ionisation energy 

  • electronegativity

Solution

A.

the solubility of their hydroxides in water

Electronegativity, as well as ionisation energy both, usually decrease on moving downward a group with an increase in atomic number. The hydroxides and sulphates of alkaline earth metals are ionic solids and the solubility of ionic solids is governed by two factors viz, lattice energy and hydration energy. For solubility hydration, energy > lattice energy.
Hydration energy varies inversely with size, ie, decreases with increase in size. However, lattice energy in case of sulphates, remains almost same with an increase in the atomic number of alkaline earth metals, due to the large size of sulphates ion. Hence, hydration energy only governs the solubility of alkaline earth metal sulphates decrease as the hydration energy decreases on moving downward the II A group.

On the other hand, in the case of hydroxides, the lattice energies are different because of medium size of hydroxide ions and decreases on moving from Be to Ba. This tends to increase the solubility and to overcome the counter-effect produced by the decrease in hydration energy. Hence, the solubility of alkaline earth metal hydroxides increases with increase in the atomic number of alkaline earth metals.

Some More Questions From The s-Block Elements Chapter

What are s-block elements?

Why are alkali metals not found in nature?

Lithium shows similarities to magnesium in the chemical behaviour. What is the cause of this similarity?

What is the nature of lithium compounds?

Group 1 elements are called alkali metals. Why?

Why caesium can be used in photoelectric cell while lithium can not be?

In aqueous solution, Li+ ion has lowest mobility. Why?

Lithium has highest ionisation energy in group 1 elements, yet it is strongest reducing agent. Comment.

The softness of group 1 elements increases down the group with increasing atomic number. Give reason. 

Which is the most reactive alkali metal and why?

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