Name: AB Type Ionic Crystals
Uploaded: 2019-07-19
Duration: 7 min 12 s
Description: Ionic crystals are crystalline structures that grow from ionic bonds and are held together by electrostatic attraction. Let's explore some of the common ionic crystals.

Question

What are molecular solids, and what are their characteristics? Discuss the crystal structure of dry ice.

Accepted Answer

Molecular solids: The constituent particles of molecular solids are molecules. These molecules are held together by van der Waals' forces (dispersion, dipole-dipole interaction).

Characteristics of molecular solids are given below:

(i) They are usually soft, and they possess low melting and boiling points.

(ii) Their vapour pressures are relatively higher and they are volatile.
(iii)They possess low heats of fusion.
(iv) They are not much soluble in polar solvents.
(v) They act as bad conductors of electricity and act as insulators due to the absence of mobile electrons.

Structure of dry ice: Dry ice is the solid form of carbon dioxide. In its lattice, carbon dioxide molecules are held together by van der Waals' forces.

When dry ice is formed under specific conditions, it can exhibit a unique crystalline appearance. Under normal atmospheric pressure, dry ice is stable at temperatures below $- 78 . 5^{°}$ . At this temperature, dry ice forms a solid with a structure similar to the face-centred cubic (fcc) arrangement, with carbon dioxide molecules arranged in a regular pattern.

In the fcc structure, carbon atoms occupy the corners of a cube, and each face of the cube contains an oxygen atom. The carbon and oxygen atoms are connected by covalent bonds, forming a network of molecules. This arrangement allows for the formation of a three-dimensional lattice, where each carbon dioxide molecule interacts with its neighbouring molecules through weak intermolecular forces known as van der Waals' forces.

Arrangement of carbon dioxide molecules in the crystal lattice is as shown below:

What are molecular solids, and what are their characteristics? Discuss the crystal structure of dry ice.

Important Questions on Solid State

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