why does graphite have a high melting point
Graphite is another allotrope of carbon. Like diamond, its properties include:
However, unlike diamond, graphite is: Graphite is used inside pencils. It slips easily off the pencil onto the paper and leaves a black mark. Graphite is also a component of many lubricants, for example bicycle chain oil, because it is slippery. Like diamond, graphite has a giant molecular structure. As its covalent bonds are very strong, and there are many of them, a lot of energy would be needed to separate atoms. This makes graphite's melting point and boiling point very high. However, each carbon atom is only covalently bonded to three other carbon atoms, rather than to four as in diamond. Graphite contains layers of carbon atoms. The layers slide over each other easily because there are only weak forces between them, making graphite slippery. Graphite contains delocalised electrons (free electrons).
These electrons can move through the graphite, carrying charge from place to place and allowing graphite to conduct electricity. Giant covalent structures contain a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. The atoms are usually arranged into giant regular lattice A lattice is a regular grid-like arrangement of atoms in a material. - extremely strong structures because of the many bonds involved. The graphic shows the molecular structure of diamond and graphite: two allotropes Allotropes are structurally different forms of an element. They differ in the way the atoms bond with each other and arrange themselves into a structure. Because of their different structures, allotropes have different physical and chemical properties. of carbon, and of silica (silicon dioxide).
Very high melting points - Substances with giant covalent structures have very high melting points, because a lot of strong covalent bonds must be broken. Graphite, for example, has a melting point of more than 3,600jC. Variable conductivity conduct To allow electricity, heat or other energy forms to pass through. electricity. Graphite contains free electrons Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. , so it does conduct electricity. Silicon is semi-conductive - that is, midway between non-conductive and conductive. Graphite is a form of carbon in which the carbon atoms form layers. These layers can slide over each other, so graphite is much softer than diamond. It is used in pencils, and as a lubricant A substance used to reduce the friction between two solid surfaces.
Each carbon atom in a layer is joined to only three other carbon atoms. Graphite conducts electricity. Diamond is a form of carbon in which each carbon atom is joined to four other carbon atoms, forming a giant covalent structure. As a result, diamond is very hard and has a high melting point. It does not conduct electricity. Silica, which is found in sand, has a similar structure to diamond. It is also hard and has a high melting point, but contains silicon and oxygen atoms, instead of carbon atoms. The fact that it is a semi-conductor makes it immensely useful in the electronics industry: most transistors are made of silica. Buckminsterfullerene is yet another allotrope of carbon. It is actually not a giant covalent structure, but a giant molecule in which the carbon atoms form pentagons and hexagons - in a similar way to a leather football. It is used in lubricants.
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