Question

For a crystal of sodium chloride, state:
A.The type of lattice in which it crystallizes.
B.The coordination number of each sodium ion and chloride ion in the crystal lattice.
C.The number of sodium ions and chloride ions present in a unit cell of sodium chloride.
D.The structural arrangement of the sodium chloride crystal.

Answer 1

crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter.

Complete step by step answer:
The salient features of sodium chloride ($NaCl$) structure are:

A: Chloride ions are fcc(face centred cubic) type of arrangement, i.e., it contains chloride ions at the corners and at the centre of each face of the cube.

B: It is obvious that each chloride ion is surrounded by six sodium ions which are disposed towards the corners of a regular octahedron. We may say that cations and anions are present in equivalent positions and the structure has 6:6 coordination

C: We may say that cations and anions are present in equivalent positions and the structure has 6:6 coordination. The structure of sodium chloride consists of eight ions a unit cell, four are $N{{a}^{+}}$ ions and the other four are $C{{l}^{-}}$ ions. Hence, a unit cell contains four sodium chloride atoms

D: The structural arrangement of the sodium chloride crystal is cubic close packing with $Cl^-$ ions at corners and face centres and Na+ ions at edge centres and body centre, with respect to $Na^+$ ions it is octahedral.

Note: Other than fcc there are two other cubic systems such as bcc(body centred cubic) and ccp (cubic close packed structures. The body-centred cubic system has one lattice point in the centre of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell.