Why does diamond have a higher melting point than silicon?
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The bond energy of Si is generally considered to be lower than that of the C-C, so a simple explanation is that diamond has a stronger bond.
Both diamond and silicon have a three dimensional network structure. Diamond consists of tetrahedral bonded carbon atoms whereas silicon has many polymorphs (crystal structure which are temperature dependant). As you heat silicon up the crystal structure changes. Silicon does not melt "congruently" to give a liquid of the same composition, it decomposes at around 2700 0C .
Both diamond and silicon have a three dimensional network structure. Diamond consists of tetrahedral bonded carbon atoms whereas silicon has many polymorphs (crystal structure which are temperature dependant). As you heat silicon up the crystal structure changes. Silicon does not melt "congruently" to give a liquid of the same composition, it decomposes at around 2700 0C .
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Explanation:
Physical Properties
Diamond does not melt at ordinary pressures. It converts to graphite and sublimates at about 3680 °C.
Silicon carbide sublimates at about 2700 °C.
Explanation
The difference appears to be caused by the differences in bond lengths and bond strengths.
Silicon carbide has a
C-Si
bond length of 186 p.m. and a bond strength of 318 kJ/mol.
Diamond has a much shorter
C-C
bond length (154 pm) and stronger bonds (348 kJ/mol).
Thus, it takes more energy to vaporize diamond, and diamond has the higher sublimation temperature.
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