CBSE Class 12-science Answered

Crystalline solids are classified into four categories:

I.Ionic solids: These are crystalline solids in which the constituent particles are positive and negative ions.

E.g.In case of NaCl, Na+ and Cl- ions are held together by strong electrostatic forces of attraction.

II. Molecular solids: In these solids, the constituent particles are molecules.

a. They may be non-polar molecules like H₂, Cl₂ held together by weak dispersion or London forces.

b. They may be polar molecules like HCl held together by dipole-dipole forces of attraction.

c. They contain hydrogen bond linked to highly electronegative atom like oxygen atom in H₂O held by strong hydrogen bonds.

III.Covalent or network solids: They are solids in which the constituent particles are non-metal atoms linked to adjacent atoms by covalent bonds. E.g. In diamond, the carbon atoms are linked to each other by covalent bonds.

IV.Metallic solids: In these solids, the constituent particles are positively charged metal ions and free electrons. E.g. Fe, Cu