Question

Give the allotropic forms of (i) carbon (ii) phosphorus (iii) sulphur

Short answer

Answer: Carbon has two main allotropes: Diamond (covalently bonded tetrahedral structure, hard and transparent) and Graphite (sheets of hexagonal rings, good lubricant and conductor). Phosphorus has three common allotropes: White Phosphorus (reactive tetrahedral molecule, toxic and glows in the dark), Red Phosphorus (stable chains of covalent bonds, used in safety matches), and Black Phosphorus (layered structure, good conductor and suitable for semiconductors). Sulfur has two significant allotropes: Orthorhombic Sulphur (crown-like cyclic molecule, stable and used in various industries) and Monoclinic Sulphur (less stable cyclic molecule, needle-like crystal structure formed by heating and cooling).

Step-by-step solution

(i) Allotropic forms of Carbon)

Carbon has two main allotropic forms: 1. Diamond - In the diamond allotrope of carbon, each carbon atom is covalently bonded to four other carbon atoms. This forms a tetrahedral structure that gives diamond its characteristic hardness and crystal lattice structure. Diamond is optically transparent and has a high refractive index, making it a highly desirable gemstone material. 2. Graphite - In the graphite allotrope of carbon, carbon atoms are arranged in sheets of hexagonal rings, with each carbon atom bonded to three others. These sheets are stacked together and bonded with weak van der Waals forces, giving graphite its characteristics of being a good lubricant and highly conductive. Graphite is used in products such as pencils and batteries.

(ii) Allotropic forms of Phosphorus)

Phosphorus has several allotropic forms, but the three most common are: 1. White Phosphorus (P4) - White phosphorus is the most reactive allotrope of phosphorus and consists of a tetrahedral molecule with each atom covalently bonded to three others. It is highly toxic and glows in the dark due to slow oxidation in the air. White phosphorus is used in fireworks and military applications. 2. Red Phosphorus - Red phosphorus consists of long chains or polymeric structures of phosphorus atoms connected by covalent bonds. It is safer and more stable than white phosphorus and is used primarily for making safety matches. 3. Black Phosphorus - Black phosphorus is the least reactive allotrope and has a layered structure similar to graphite. It is a good conductor of electricity and is considered to be a promising material for semiconductor devices.

(iii) Allotropic forms of Sulphur)

Sulphur has several allotropic forms, but the two most significant are: 1. Orthorhombic Sulphur (S8) - Orthorhombic sulphur is the most stable and common allotrope of sulphur. It consists of eight sulfur atoms arranged in a crown-like cyclic molecule. This molecule is held together by single covalent bonds and has a yellow color. Orthorhombic sulphur is used in the production of sulfuric acid, rubber vulcanization, and the manufacturing of various chemicals and fertilizers. 2. Monoclinic Sulphur (S8) - Monoclinic sulphur is a less stable allotrope of sulphur, which also contains eight sulfur atoms in a cyclic molecule, but has a slightly different molecular arrangement. It has a needle-like crystal structure and is formed by heating orthorhombic sulphur above 95.5°C and then slowly cooling it.