Carbon is found in organic compounds, in carbonates, etc.

Allotropic forms of carbon

Allotropy is the appearance of an element in different forms in the same physical state.

Crystalline Allotropes



Brittle, crystalline, non-volatile, resistant to melting and chemical attack.
Soft, grayish-black, crystalline, soft feel and metallic luster.
RD – 3.52, fusible, melts at 3500°C
RD – 2.2, melts at 2527°C under pressure.
May be colorless, blue, green, yellow, red due to impurities.
Is grayish-black and leaves mark on paper (pencil).
ยต = 2.5. Transparent to light and x-rays.
Opaque to light.
Insoluble in known reagents.
Insoluble in known reagents.
Good conductor of heat, not electricity.
Good conductor of heat and electricity.
Chemically inert.
Is oxidized in a mixture of K2Cr2O7 and H2SO4.
At 800°C, in O2 it is oxidized to CO2
At 700°C, in O2 it is oxidized to CO2
At 1500°C, O2 absent, it becomes graphite.
Heated in absence of O2, it is stable.
Atoms tetrahedrally arranged – rigid, compact, hard, dense, high melting point. No free electrons to conduct electricity.
Atoms arranged in planes – hexagonally. Planes held by weak attraction – can slide over, soft and greasy. Free electrons to conduct electricity.

Amorphous Allotropes

Wood Charcoal

formed by the destructive distillation of wood – heating in the absence of air, and collecting volatile substances – wood charcoal, pyroligneous acid, wood tar and combustible gases are formed.
Physical properties
1.        Black, porous, brittle, amorphous.
2.        Can absorb gases and liquids.
3.        Insoluble in common solvents.
Chemical properties
1.        Burns at 400°C.
C + O2 CO2
2.        At high temperatures, under the effect of a catalyst, it combines with hydrogen to form methane.
C + 2H2 CH4
3.        With sulfur vapor it forms a colorless toxic liquid, carbon disulphide.
C + 2S CS2
4.        For the extraction of metals, reducing agent.
C + ZnO Zn + CO
C + PbO Pb + CO
Fe2O3 + 3C 2Fe + 3CO
5.        When heated with concentrated sulphuric acid, charcoal reduces it.
C + 2H2SO4 2H2O + CO2 + SO2
6.        When heated with concentrated nitric acid, charcoal reduces it.
C + 4HNO3 2H2O + CO2 + 4NO2
7.        When steam is passed over hot charcoal water gas is formed.
C + 2H2O CO + H2
8.        Calcium oxide and coke form calcium carbide when heated.
CaO + 3C CaC2 + CO
1.        as a fuel,
2.        as an absorbing agent,
3.        in gunpowder


When oil is heated in insufficient air, lampblack is formed (oil impurities can be removed by chlorine). It is used to make shoe-polish, printers ink, carbon paper, typewriter ribbons, etc.

To show that all allotropes contain equal amounts of carbon, equal weight are placed in trays and heated in oxygen. Carbon dioxide is absorbed by KOH, and the increase in weight noted. It is equal for equal weights of allotropes.

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