8th Class Science Related to Competitive Exam NCERT Summary - Carbon

Carbon The Carbon

The Carbon

• Group 14 (IVA) consists of carbon, silicon, germanium, tin and lead. Carbon is a non-metal, silicon and germanium are metalloids, tin and lead are metals.
  • Carbon is a very important element. This is due to 3 reasons:
• Carbon is a tetravalent atom. It may form four covalent bonds in different directions tetrahedrally.
  • Carbon has several allotropes, three of which are common.

(i)   Amorphous carbon is coal and soot. The carbon molecules are covalently bonded but there is no order of arrangement.

(ii)   Graphite occurs when carbon forms flat covalent networks. These flat "sheets" are not bonded to each other, making them free to slide past each other. Graphite composes the "lead" in pencils. Since graphite contains free electrons, it is a good conductor of heat and electricity. Graphite is used as a lubricant in fast-moving machinery since graphite is soft and slippery.

(iii) Diamond occurs when carbon forms a three-dimensional covalent network. Diamonds are different from graphite and amorphous carbon. They are transparent, brilliant-looking and incredibly hard. Diamond only forms at heat and intense pressure. It is a bad conductor of heat and electricity, as there are no free electrons present in it.

• Carbon compounds are of two types: inorganic and organic.

Organic and Inorganic Compounds

• The compounds that have a mineral origin fall under the category of inorganic compounds.
• The compounds having a plant or animal origin, are classified as organic compounds.
• In spite of the fact that organic compounds were originally derived from living sources. Today, most of these compounds can be synthesised.
• Organic compounds are known to contain mainly hydrogen and carbon.
  • Application of Organic Compounds in Daily Life:
• Ethylene: This gas is produced naturally by most fruits, and it promotes ripening.
• Alkanes: They are used in hydrocarbon fuels (petrol, diesel, propane, butane, kerosene, etc.)
• Alkenes: They occur in fats (unsaturated fats have C = C bonds in)
• Polymers: These long chain molecules feature in proteins, plastics, rubber and many other synthetic materials.
• Alcohols: To make alcoholic drinks (the obvious case with ethanol), to act as general solvents (methanol is in methylated spirit, isopropyl alcohol is in a lot of cleaning agents).
• Carboxylic acid: Fatty acids (a type of carboxylic acid) are used to make soaps and detergents, acetic acid is in vinegar.