Carbon
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| Discuss Carbon CARBON AND ITS ALLOTROPES
Carbon is a non-metallic element belonging to the group IV of the periodic table. In the free state it occurs in the form of diamond graphite and coal. In the combined state it occurs as CO2 (in air), as carbonates (in rocks and minerals) and as hydrocarbons (in petroleum). Carbon is an essential element and it forms so many compounds that it has a chemistry of its own called organic chemistry. It is present in all living beings, plants and animals, as proteins, carbohydrates, fats and other complicated compounds.
PROPERTIES
- It is a non- metal
- Atomic number 6
- Relative atomic mass 12.011
- Melting point ~3550OC
- Boiling point ~4289OC
- Shows allotropy (occurs as diamond, graphite, coal and lampblack)
PROPERTIES RELATIVE TO THE GROUP
- It has the smallest atomic radius as compared to all other members of this group.
- It has the lowest atomic volume.
- Is the most electronegative in the IV group
- Has the highest ionisation energy
- Is most compact (i.e. it is the hardest and has the highest melting and boiling points)
- It shows the property of catenation. In group IV it shows the maximum property of catenation.
ALLOTROPIC FORMS OF CARBON
What is allotropy?
Allotropy is defined as the property due to which an element exists in different physical form but the same chemical form. These different forms are called allotropes of the element.
Carbon has two main allotropic forms
- DIAMOND
Diamond is the hardest known mineral (it has a hardness of 10 on the Mohs’ scale). The hardness of a diamond results from the covalent crystal structure, in which each each carbon atom is linked by covalent bonds to four others situated at the corners of a tetrahedron. Diamond crystallises in the cubic system usually as octahedra or cubes, under great pressure.
PROPERTIES
- Relative density 3.52
- Is extremely hard
- It is transparent to x-rays and glows in ultra-violet light.
- Has highly refractive crystals. Thus its refractive index is very high (2.45)
- The C-C bond length is 0.154 nm and the bond angle is 109.5O.
- It is chemically inert.
USES
- It is used as a gemstone
- Black diamond is used in the manufacture of cutting tools
- Diamond dies are used for drawing thin wires
- GRAPHITE
Graphite is a soft, black and slippery substance. It occurs naturally and can be manufactured artificially. In graphite the carbon atoms are arranged in layers, in which each carbon atom is surrounded by three others to which it is bound by single or double bonds. Theese layers are held together by weak van der Waal’s forces.
PROPERTIES
- It is a good conductor of heat and electricity.
- Relative density 2.25
- The C-C bond length is 0.142 nm
USES
- For the lining and as electrodes in an electric furnace
- In the manufacture of refractory crucibles
- Is an important constituent in the lead pencil’s lead
- As a moderator in a nuclear reactor
- As a lubricator in machinery which work at very low or very high temperatures.
