Q52 of 149 Page 212

What is the number of valence electrons in:
(a) sodium ion, Na⁺

(b) oxide ion, O^2-

(a) 8 is the number of valence electrons in sodium ion, Na⁺ has the electronic configuration of 2, 8.

(b) 8 is the number of valence electrons in oxide ion, as O^2- have the electronic configuration of 2, 8.

The atomic number of an element X is 8 and that of element Y is 4. Both these elements can exhibit a valency of:

The isotopes of an element contain:

Atom A has a mass number 209 and atomic number 82.

Atom B has a mass number 209 and atomic number 83.

(i) How many protons atom A has?

(ii) How many protons atom B has?

(iii) Are atoms A and B isotopes of the same element?

Which of the following pairs are isotopes? Give reasons for your choice:

(i) or (ii)

What is the number of valence electrons in:(a) sodium ion, Na+(b) oxide ion, O2-