Question

Coordination number of the NaCl crystal will be____?
(A) 8:8
(B) 6:6
(C) 4:4
(D) 2:2

Answer 1

Hint : The coordination number of an atom is defined as the number of atoms attached to this atom. The coordination number depends on the radius ratios of cation to anion.

Complete step by step solution :
Let’s look at the answer to this question:
NaCl is the chemical formula of sodium chloride. It is commonly known as common salt. It contains sodium cation and chloride anion. Sodium chloride forms beautiful yellow-whitish coloured crystals. It crystallizes into FCC lattice that is face centered cubic crystal.
Its crystal is also known as rock salt crystal. It is an ionic compound. It is also known as table salt as it is used in cooking.
In NaCl chemical formula we can see that Na and Cl ions are present in 1:1 stoichiometry which means that for each Na ion there is a Cl ion and vice-versa.
In NaCl crystal, each sodium ion is surrounded by 6 chloride ions and each chloride ion is surrounded by 6 sodium ions. So, the coordination number of NaCl as per definition will be 6:6.

So, the correct answer is “Option B”.

Note : The sodium cation is a small cation so it cannot go into higher coordination numbers like 8:8. This is because steric hindrances will increase and the crystal will become unstable. Salts of cesium metal undergoes 8:8 coordination number. This is because the cation of cesium metal is very large in size so it can accommodate 8 other atoms around it.