Diamond and graphite are allotropes of carbon. The molecular structure of diamond is strong because of the existence of many covalent bonds. The presence of these covalent bond makes diamond to have high melting and boiling points. Other important properties of diamond are: transparency and shiny appearance, hardness, low electrical conductivity but high thermal conductivity,water insolubility, because of its electron affinity.
Chemically, diamond does not react with most of alkalis and acids but it does accept hydrocarbons.
Diamond hardness (10, on Mohs hardness scale) makes it suitable as cutting tools used in oil exploration industry or in construction industry.
Diamond high reflection index and it's brilliance make it suitable for jewellery industry. The appearance of pure diamond is usually pale, but inclusions of other minerals and impurities give diamonds all sort of colors, like yellow, because of nitrogen or blue, due to boron element.
Graphite shares many properties with diamond, such that the high melting point or the water insolubility. Unlike diamond, which shines and it is transparent, graphite appearance is opaque and black. Graphite is also a good electrical conductor, because of delocalized electrons, and it's slippery property is used as lubricant or in pencils.
Unlike diamond, where each atom of carbon is bonded to 4 atoms of carbon, the atom of carbon in graphite is bonded to 3 atoms of carbon, hence, the molecular structure becomes weaker, compared to the molecular structure of diamond. The slippery property of graphite is given by the presence of layers of carbon.
Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. Diamond is an optically isotropic crystal that is transparent to opaque.
Diamonds have a range of unique properties:
- Diamond is the hardest known natural material on Earth.
- Diamonds do not conduct electricity well, although some are semiconductors.
- Diamond conducts heat 5 times faster than copper, which is why it feels cold to the touch.
- Pure diamond is the most transparent material known. It reflects visible light, ultra-violet light, and infrared light, and all the frequencies in between.
- Diamond can be an insulator or a conductor, so it can either allow electricity to pass through or block it.
- Diamond can survive intact in environments that will destroy other materials. It can survive severe physical, chemical and radioactive forces.
- If you place diamonds inside the human body they will not trigger an immune response.
- Diamond is the hardest natural material.
- Diamond is also the least compressible and stiffest substance.
- It is an exceptional thermal conductor - 4 times better than copper - which gives significance to diamonds being called 'ice'.
- Diamond has an extremely low thermal expansion, is chemically inert with respect to most acids and alkalis, is transparent from the far infrared through the deep ultraviolet, and is one of only a few materials with a negative work function (electron affinity).
- Diamond can burn if subjected to a high temperature in the presence of oxygen.
- Diamond has a high specific gravity; it is amazingly dense given the low atomic weight of carbon.
- Diamond has the highest reflectance and index of refraction of any transparent substances.
- Diamond gemstones are commonly clear or pale blue, but colored diamonds, called 'fancies', have been found in all the colors of the rainbow. Boron, which lends a bluish color, and nitrogen, which adds a yellow cast, are common trace impurities. Two volcanic rocks that may contain diamonds are kimberlite and lamproite.
- Diamond crystals frequently contain inclusions of other minerals, such as garnet or chromite. Many diamonds fluoresce blue to violet, sometimes strongly enough to be seen in daylight. Some blue-fluorescing diamonds phosphoresce yellow (glow in the dark in an afterglow reaction).
Graphite is a soft grayish-black greasy substance. The word ‘graphite’ comes from a Greek word meaning ‘to write’. The lead in our writing pencils is graphite mixed with clay. Graphite is also known as black lead or plumbago.
The physical properties of graphite are as follows:-
has a high melting point, similar to that of diamond. In order to melt graphite, it isn't enough to loosen one sheet from another. You have to break the covalent bonding throughout the whole structure.
has a soft, slippery feel, and is used in pencils and as a dry lubricant for things like locks. You can think of graphite rather like a pack of cards - each card is strong, but the cards will slide over each other, or even fall off the pack altogether. When you use a pencil, sheets are rubbed off and stick to the paper.
has a lower density than diamond. This is because of the relatively large amount of space that is "wasted" between the sheets.
is insoluble in water and organic solvents - for the same reason that diamond is insoluble. Attractions between solvent molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite.
conducts electricity. The delocalised electrons are free to move throughout the sheets. If a piece of graphite is connected into a circuit, electrons can fall off one end of the sheet and be replaced with new ones at the other end.