Question

An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.

Classify X and Y as metal (s), non-metal (s) or metalloid (s)

Answer 1

Classification of X and Y:

Electronic configuration of X with atomic number $17$= $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^5$
Electronic configuration of Y with atomic number $20$= $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^2$

From the electronic configuration of X, it needs one more electron to complete its octet in the outermost shell to gain stability.

• Therefore, it has a tendency to accept electrons and shows electronegative nature which is a property of non-metals.
• Therefore, X is a non-metal.

The electronic configuration of Y requires the loss of two electrons to complete its octet in the outermost shell to gain stability.

• Therefore, it has a tendency to lose electrons and shows electropositive nature which is a property of metals.
• Therefore, Y is a metal.

It can be found that X is Chlorine $\left(\mathrm{Cl}\right)$ and Y is Calcium$\left(\mathrm{Ca}\right)$.