# The elements 4Be, 12Mg and 20Ca, each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the modern periodic table. - Science

The elements 4Be, 12Mg and 20Ca, each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the modern periodic table. Answer the following questions associated with these elements, giving reason in each case:

(a) In which group should they be?

(b) Which one of them is least reactive?

(c) Which one of them has the largest atomic size?

#### Solution

(a) All three elements have valency 2. Thus, they should be present in group 2 of the periodic table.

(b) On going down a group in the periodic table, the reactivity of an element increases because of decrease in the effective nuclear charge and increase in the atomic size; this makes the removal of valence electrons easy. Thus, among the given elements, 4Be is the least reactive element.

(c) On going down a group in the periodic table, the atomic size of elements increases because of the addition of new shells. Thus, among the given elements, 20Ca has the largest atomic size.

Concept: Periodic Properties
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