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The S-Block Elements

Question
CBSEENCH11007070
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Discuss the general trends in ionisation enthalpy and electropositive character of alkali metals.

Solution

Alkali metals possess lowest ionisation enthalpies in their respective periods. However, within the group, the ionisation enthalpies of alkali metals decrease down the group.
Reason: The atoms of alkali metals are largest in their respective periods, therefore, the outermost electrons, which are far away from the nucleus, experience a less force of attraction with the nucleus and hence can be easily removed. Decrease in ionisation enthalpy, on moving down the group, is due to the increase in the size of the atoms of alkali metals and increase in the magnitude of screening effect is by virtue of an increase in the number of intervening electrons.
Electropositive character: On account of their low ionisation enthalpies, these metals have a strong tendency to lose their valence electrons and thus change into positive ions. Consequently, alkali metals are strongly electropositive or metallic in character. As this tendency for losing electron increases down the group, the electropositive character increases.

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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