Question

Write a short note on ionic crystals.

Answer 1

Ionic crystals have at least two atoms in their basewhich are ionized. Charge neutrality demands that the total charge in the base must be zero; so we always need ions with opposing charge.The binding between the ions is mostly electrostatic and rather strong (binding energies around 1000 kJ/mol); it has no directionality.Ionic crystals thus can be described as an ensemble of hard spheres which try to occupy a minimum volume while minimizing electrostatic energy at the same time (i.e. having charge neutrality in small volumes, too).There are no free electrons, ionic crystals are insulators.Ionic crystals come in simple and more complicated lattice types; the latter is true in particular for oxides which are often counted among ionic crystals. Some prominent lattice types follow

Answer 2

★ Answer :

Lattice defects in ionic crystals are interstitial ions and ion vacancies. In crystalline sodium chloride NaCl a cation vacancy $\sf{VNa^{+}}$ is formed. Ionic crystals have at least two atoms in their base which are ionized. Charge neutrality demands that the total charge in the base must be ionized.

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★ Properties :

• Ionic crystals are hard

• They have high melting points

• They are brittle.

• They have higher enthalpies of fusion and vaporization than molecular compounds.

• They conduct electricity but only when they are dissolved in water.