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Question

# With respect to diamond and graphite, which of the statements given below is/are correct?

A
Graphite is harder than diamond.
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B
Graphite has higher electrical conductivity than diamond
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C
Graphite has higher thermal conducitivity than diamond.
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D
Graphite has higher C - C bond order than diamond
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Solution

## The correct options are B Graphite has higher electrical conductivity than diamond D Graphite has higher C - C bond order than diamondSince all the four valence shell electrons on each C-atom are used up in making four covalent bonds with other C-atom, therefore the average value of C-C bond order in diamond is one. There is no free electron left in the diamond crystal to carry electricity. Thus, diamond is a bad conductor of electricity. Heat conductivity in non-metals is due to lattice vibrations (Photons). So, when diamond is heated, thermal vibrations are rapidly transmitted through diamond, and it acts as a good conductor of heat. It is insoluble in all solvents. The average value of (C-C) bond order in graphite is 1.33. Since each C-atom in graphite is sp2 hybridised and is corrected to three others by one doubles and two single bonds. ∴ Bond order = Double bond + 2 single bondNo. of atoms attached to other = 2+23 = 43 = 1.33 Graphite is composed of flat two-dimensional sheets or layers of carbon atom. Each sheet or layer consists of flat hexagonal rings of C-atoms and may be regarded as a fused system of benzene rings, In each layer, each C-atom is linked to three C-atoms by C-C covalent bond. The C-C bond length in each hexagonal ring is 141.5 pm, as each C-atom is sp2 hybridised, i.e., only three of the valence electrons of each C-atom are involved in forming σ bond (using sp2 hybrid orbitals). The fourth electron forms a π- bond The π - electrons are delocalized over the whole sheet, and as they are mobile, graphite conducts heat and electricity. Conductance can occur in a sheet (layer) but not from one sheet to another.

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