Question

Based on the group valency of elements state the formula lot the following giving justification for each : (i) Oxides of 1st group elements, (ii) Halides of the elements of group 13, and (iii) Compounds formed when an element of group 2 combines with, an element of group 16.

Answer 1

(i) The valency of the group of elements is 1 and that of oxygen is 2
⇒ H    O
     1     2       [Cris cross]

⇒ H₂O is the formula for their oxides.
(iii) The valency of the Group 2 elements is +2 and that off Group 16 elements is -2
⇒ Mg    O
     2        2  [Cris cross]
⇒ MgO is the formula. 

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Answer 2

(I) valency of Grp 1 elements is 1.

Valency of oxygen is 2

Element: M O

Valency: 1 2

= M2O

The formula for Grp 1 oxides is M2O, where M is the Grp 1 element and O is oxygen.

(II) Grp 13 elements has valency 3.

Valency of halogens is 1.

The compound formed is:

Element : M X

Valency: 3 1

=MX3

Formula of the halides of Grp 13 is MX3, where M is the Grp 13 element and X is halogen.

(III) Grp 2 elements have valency 2 and valency of Grp 16 elements is also 2.

Therefore, formula of the compound is MN, where M is the Grp 2 element and N is the Grp 16 element.

Element: M N

Valency: 2 2

=MN