Why does SiC have a high melting point?Why is its melting point higher than LiF?LiF has an ionic bond; SiC has a covalent bond, so shouldn't LiF have a higher melting point? In reality SiC's...

Why does SiC have a high melting point?
Why is its melting point higher than LiF?

LiF has an ionic bond; SiC has a covalent bond, so shouldn't LiF have a higher melting point? In reality SiC's melting point is more than 2000 degrees C and LiF is 870 degrees C.

Asked on by jenjen456

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enotechris's profile pic

enotechris | College Teacher | (Level 2) Senior Educator

Posted on

Silicon Carbide (industrially known as Carborundum) is extremely rare in nature, but has been produced in quantity since the 1890's.  Its hardness has found many uses in industry;  diamond jewelry has been produced by this compound that have nearly fooled experts.  The basic structure is a tetrahedron, similar to a molecule of methane, which contains a carbon surrounded by 4 hydrogen atoms.  Substitute 4 silicon atoms for the hydrogen and you have a molecule of silicon carbide.  Although the silicon is held in the tetrahedral structure by covalent bonds with the carbon, their interaction is such that a slight ionic bond is created as well; the carbon becoming slightly negative and the silicons slightly positive.  The polar qualities, or intermolecular forces, similar to what is found in water molecules, cause the various layers of tetrahedrons to adhere strongly to each other.  Overcoming these forces takes a substantial quantity of heat, thus the high melting point of SiC.

Lithium Fluoride, although strongly ionically bonded, has no polar qualities, so its melting point is far less.

See link for structure diagrams:


revolution's profile pic

revolution | College Teacher | (Level 1) Valedictorian

Posted on

Silicon carbide (SIC), also known as carborundum is a compound of silicon and oxygen chemically combined together during a chemical reaction. It is extremely rare in the world, and is found in minute quantities. It has been used in car brakes, bulletproof vests for the policeman and ceramic plates for house usage. Its melting point is 2730 degree C, which is quite high. The reason for the high degree in temperature was that despite being covalently bond, it also has a ionic bond with it, which positive and negative ions attracting each other. The attractive forces between the molecules, or the intramolecular forces that exists between them, like water is very strong and is quite hard to break, unless huge amount of energy is used.

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