Question

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.(All India - 2019)

Answer 1

Based on the group valency of elements, the molecular formula of the following compounds are:

1. Oxide of first group elements: M2O
2. Halide of the elements of group thirteen: AX3
3. Compound formed when an element, A of group 2 combines with an element, B of group seventeen: AB2

• Justification of 1. :Oxide has valency 2 and M(suppose) is the first group element, so M has a valency of 1. Hence the formula is M2O.
• Justification of 2. :Halide(X) has valency 1 and A is a element of group 13, so it has a valency of 3, Hence formula is AX3.
• Justification of 3. : A is from group 2 so it has a valency of 2, and B is from group 17, so it has valency 1 Hence, formula is AB2.
• To calculate the valency we have to know about the number of electrons that should be taken/given to attain the octate.
• For group 1, by giving 1 electron the atom will meet octate; for group 2, by giving 2 electrons the atom will meet octate; for group 13, 3 electrons should be given to meet octate.