CBSE Class 10 Science 2019 · Paper 31/1/1 · Question 8

Periodic Classification of Elements 3 marks Medium

Based on the group valency of elements write the molecular formula of the following compounds giving justification for each :

(i)Oxide of first group elements.
(ii)Halide of the elements of group thirteen, and
(iii)Compound formed when an element, A of group 2 combines with an element, B of group seventeen.

Answer

The formulae are $M_{2} O$ , $MX_{3}$ and $AB_{2}$ , worked out from the valencies of the group elements.

(i)

M_{2} O

(for example

Na_{2} O

): a group 1 element has

1

valence electron and valency

1

, while oxygen has valency

2

, so two atoms of the metal combine with one oxygen atom. (ii)

MX_{3}

(for example

AlCl_{3}

): a group 13 element has

3

valence electrons and valency

3

, while a halogen X has valency

1

(

8 - 7

), so three halogen atoms combine with one atom of the element. (iii)

AB_{2}

(for example

MgCl_{2}

): A of group 2 has valency

2

and B of group 17 has valency

1

, so two atoms of B combine with one atom of A.

🔒 Step-by-step solution