Question

Chemical compounds in which anions and cations are held together by electrostatic force of attraction are known as ionic compounds. Cations and anions are charged species which are formed by losing and gaining electron(s) respectively to attain the nearest noble gas configuration or stability. Usually metals lose their valence electrons to form cations while non-metals accept electrons and form anions. Being held by a strong electrostatic force of attraction between ions, ionic compounds have high melting and boiling points.

(ii) To form an ionic compound, element Y accepts two electrons from X. Guess the elements X and Y from the options given below:

• A. X: Sodium, Y: Chlorine
• B. X: Chlorine, Y: Sodium
• C. X: Magnesium, Y: Oxygen
• D. X: Oxygen, Y: Magnesium

Answer 1

The correct option is C X: Magnesium, Y: Oxygen

To attain the nearest noble gas configuration,

• an atom gains, loses or shares electron(s).
• an atom with more than four valence electrons tends to gain electron(s).
• an atom with less than four valence electrons tends to lose electron(s).

Electronic configuration of few elements is as following:
$$\begin{array}{cccc}\text{Element}& \text{Atomic no.}& \text{Electronic configuration}& \text{Nearest noble gas configuration}\\ \text{Sodium}& \text{11}& \text{2, 8, 1}& \text{2, 8}\\ \text{Magnesium}& \text{12}& \text{2, 8, 2}& \text{2, 8}\\ \text{Chlorine}& \text{17}& \text{2, 8, 7}& \text{2, 8, 8}\\ \text{Oxygen}& \text{8}& \text{2, 6}& \text{2, 8}\end{array}$$
As element Y accepts two electrons, it should have six valence electrons so that it can complete its octet. Hence, element Y is oxygen.
Similarly, element X is magnesium as it has two valence electrons and by donating these, it attains nearest noble gas configuration (complete octet).
Thus, the ionic compound will be MgO (Magnesium oxide).