Question

Two elements X and Y belong to group 1 and 2 respectively in the same period of periodic table.

Compare them with respect to:

(i)The number of valence electrons in their atoms

(ii)Their valencies

(iii)Metallic character

(iv)The sizes of their atoms

(v)The formulae of their oxides

(vi) The formulae of their chlorides

Answer 1

(i) Valence electrons in any atom = Group number
So, The number of valence electrons in element X(group no. is 1) is 1 while in element Y(group no. is 2) is 2.

(ii) Since valence electrons in element X= 1

So, to get stable gas electronic configuration, it will lose one electron. So, The valency of X = 1 whereas The valence electrons in element Y = 2 . So, to get stable gas electronic configuration, it will lose two electrons. So, the valency of Y is 2.

(iii) Since metallic character decreases on moving from left to right in a period because the effective nuclear charge increases and tendency to lose electrons decreases. Hence, X lies in group 1 and Y in group 2, So, X will have more metallic character than Y.

(iv) The size of the atom decreases when moving from left to right in a period as across a period, the electrons are increased and added to the same shell, which increases the nuclear charge due to which size decreases. So, the size of X will be larger than Y.

(v) The formula of an oxide of element X is $X_{2}O$ and that of element Y is YO.
To determine the formulae of any compound, we use the criss-cross method. According to this, the numerical value of each ion is crossed over to become the subscript of the other ion.
X O
1 2
So, by criss-cross , we get the formulae $X_{2}O$ X2OX_2O
Y O
2 2
So, by criss-cross , we get the formulae $Y_2{O}_{2}orYO$

(vi) Since the valency of X is 1. Valency of chlorine is 1.
X Cl
1 1
So, by criss-cross , we get the formulae XCl
Y Cl
2 1
So, by criss-cross , we get the formulae $YC{l}_2$
So, Chloride of X = XCI

Chloride of Y = $YC{l}_2$