Questions & Answers

The coordination number of \[N{{a}^{+}}\]ion in the rock-salt structure is_______.

Answer Verified Verified
Hint: By counting the number of atoms or molecules from which sodium ion is attached, we can find the coordination number of \[N{{a}^{+}}\].

Complete step by step solution:
 We know that the Coordination number is also called Ligancy. The number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbours in a complex or coordination compound or in a crystal is known as coordination number.

Method of finding coordination number:
First identify the central atom in the chemical formula. Usually, this is a transition metal.
Then locate the atom, molecule, or ion nearest the central metal atom.
Add the number of atoms of the nearest atom/molecule/ions.
Find the total number of nearest atoms.
Rock salt is an ionic compound that occurs naturally as white crystal. The rock salt structure is a simple crystal structure of the form AX, it is adopted by sodium chloride. In the case of NaCl, it is a fcc array of anions with the cations inside the octahedral holes.
NaCl has a fcc lattice in which sodium is at all corners and chloride ions are on the face centre. Here, each ion is attached with 6 other ions. So, the coordination number of each ion is 6. Sodium ion is attached with 6 chloride ions at face centers. With a single unit 8 other units are also attached.

So, from the above explanation we can say that the coordination number of sodium ions is ‘6’.

Note: Nearest atoms or ions mean that those ions or atoms should be on the nearest distance. And these ions or atoms can be of similar type or differ.