An element X has same number of electrons in the first and the fourth shell as well as in the second and the third shell.
(a) Write down the electronic configuration of the element.
( b) Write down the group number and the period to which it belongs
( c) What is the valency of the element ?
(d ) Will it form ionic or covalent compound with the element Y (2,8,6) ?
( e) What is the nature of the oxides of X and Y ?

Explanation

(a) We know that the maximum number of electrons in the Ist and 2nd shell are 2 and 8 respectively .Since 3rd shell has the same number of electrons as the 2nd shell therefore 3rd shell also has 8 electrons.
Further since 4th shell has the same number of electrons as the 1st shell therefore 4th shell has two electrons. Therefore the electronic configuration of the element X is 2,8,8,2 Actually the element X is Ca.
(b) Since in the element X the valence electrons are present in the fourth shell , therefore the period of element X is 4 .Further since is has two electrons in the valence shell therefore its group number is 2.
( c) Valencey of the element X ( 2,8,8,2) i.e., Ca has two electrons more and the element Y (2,8,6 ) i.e., S has two electrons less than the stable electronic configuration of the nearest gas argon (2,8,8) therefore X transfers two electrons to Y to form ionic compound.

(e ) Since X is a metal therefore its oxide is basic i.e., CaO. Since Y is a non- metal therefore its oxide is acidic i.e., `SO_(2) " or " SO_(3)`