Question

Element Y accepts 3 electrons from element X to form a molecule. Guess the element Y and X from the options given below.

• A. Y = Oxygen and X = Magnesium
• B. Y = Nitrogen and X = Aluminium
• C. Y = Oxygen and X = Sodium
• D. Y = Carbon and X = Magnesium

Answer 1

The correct option is B Y = Nitrogen and X = Aluminium

- Atoms gain, lose or share electrons from their valence shell to complete their octet. This determines the valency of atoms.

- An atom with more than four valence electrons tend to gain electrons to complete its octet.

- An atom with less than four valence electrons tend to lose electrons to complete its octet.
$$\begin{array}{ccc}\text{Element}& \text{Atomic no.}& \text{Electronic configuration}\\ \text{Oxygen}& \text{8}& \text{2, 6}\\ \text{Magnesium}& \text{12}& \text{2, 8, 2}\\ \text{Nitrogen}& \text{7}& \text{2, 5}\\ \text{Aluminium}& \text{13}& \text{2, 8, 3}\\ \text{Sodium}& \text{11}& \text{2, 8, 1}\\ \text{Carbon}& \text{6}& \text{2, 4}\end{array}$$

As element Y accepts three electrons, it should have five valence electrons, so that it can complete its octet by gaining three. Hence, element Y is nitrogen.
Similarly, element X is aluminium as it has three valence electrons and by donating these, it attains nearest noble gas configuration (complete octet).