Question

(a) A metal M forms an oxide having the formula M₂O₃. It belongs to 3rd period in the modern periodic table. Write the atomic number and valency of the metal.
(b) Write the formula of chloride of metal M.
(c) What could metal M be?

Answer 1

(a) Metal M has the formula ${\mathrm{M}}_2{\mathrm{O}}_3$, from which it is clear that the
valency of M = +3
valency of O = -2

Since M is in the third period, its outer most/third shell will have three valence electrons which will give it a configuration as 2, 8, 3.

So, the atomic number of the M = 13

Hence, M will be aluminium and its formula will be ${\mathrm{Al}}_2{\mathrm{O}}_3$.

(b) Valency of metal M is +3 so it will form MCl₃ type compound with alkaline earth metals. Since M is aluminium, the compound will be AlCl_3.

(c) The atomic number of the M = 13 which means that the metal M will be aluminium.