They are crystals consisting of a three dimensional array of discrete molecules held together by weak Van der Waal's forces. Hence, intermolecular forces in such solids are weak. Some examples of simple molecules are iodine, phosphorus, sulphur, nitrogen, argon, water etc. They all form molecular crystals. Some of the important properties of simple molecular crystals are as follows
They are not good conductors of electricity. Not in solid or molten state or in solution. This is basically due to lack of electrons or ions in these solids. Molecular solids have another property which distinguished them from macro molecules. They have a relatively low melting point. This is because of their structure. They are held together in the crystal lattice by weak Vander Waal's forces there small amount of energy is usually required to break them off.
Iodine and ice are two such structures. Iodine is the most common example of a substance that forms simple molecular crystals. Iodine is solid up to 30 degree centigrade. When the solid iodine is heated the Vander Waal's forces are broken easily and the solid iodine sublimes as free iodine molecules. Iodine is purple in the vapour phase. The closely packed structure of iodine is responsible for the high density of iodine.
They are not good conductors of electricity. Not in solid or molten state or in solution. This is basically due to lack of electrons or ions in these solids. Molecular solids have another property which distinguished them from macro molecules. They have a relatively low melting point. This is because of their structure. They are held together in the crystal lattice by weak Vander Waal's forces there small amount of energy is usually required to break them off.
Iodine and ice are two such structures. Iodine is the most common example of a substance that forms simple molecular crystals. Iodine is solid up to 30 degree centigrade. When the solid iodine is heated the Vander Waal's forces are broken easily and the solid iodine sublimes as free iodine molecules. Iodine is purple in the vapour phase. The closely packed structure of iodine is responsible for the high density of iodine.