0Allotropy is the property by virtue of which an element exist in more than one form and each form has different physical properties but identical chemical properties. These different forms are called allotropes. The two common allotropic forms of carbon are diamond and graphite.
About Graphite:
Graphite is an allotrope of carbon, which is black or bluish grey with a metallic lustre and or greasy feel. It occurs in igneous and metamorphic rocks, such as marble.
Structure:
Each carbon is bonded to only three neighboring carbon atoms in the same plane forming layers of hexagonal networks separated by comparatively larger distance. The different layers are held together by weak forces, called vanderwaal’s forces. The layers can therefore, easily slide over one another. This makes graphite lubricating, soft and greasy to touch.
Properties of Graphite:
(A) It is soft and greasy in touch.
(B) Its specific gravity is 2.25 (generally).
(C) It is grayish black and opaque.
(D) It is a good conductor of heat and electricity.
(E) It occurs in hexagonal layers.
(F) It is stable and has high melting point.
Structure of Diamond:
Diamond crystals found in nature are generally octahedral (eight faced). In the structure of diamond, each carbon i linked to four other carbon atoms forming regular and tetrahedral arrangement and this network of carbon atoms extends in three dimensions and is very rigid. This strong bonding is the cause of its hardness and its high density. This regular, symmetrical arrangement makes the structure very difficult to break. To separate one carbon atom from the structure, we have to break four strong covalent bonds.
Properties of Diamond:
(A) It occurs naturally in free state and has octahedral shape.
(B) It is the hardest natural substance known.
(C) It has high specific gravity (about 3.5).
(D) It is transparent, colourless and brittle solid.
(E) It has a high refractive index (about 2.4).
(F) It is non-conductor of electricity.
