NEET Chemistry Notes p-Block Elements -Group 14 Elements: Carbon Family
Group 14 Elements: Carbon Family
Group 14 Elements: Carbon Family
Carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb) are the members of group 14. Carbon is the seventeenth most abundant element by mass in the earth’s crust. C is non-metal, Si, Ge are metalloids and Sn, Pb are metals.
Some of the important properties of group 14 elements or carbon family elements are given below :
The tendency for catenation is maximum in carbon and it decreases down the group due to steady decrease in M—M bond strength.
All the members except Pb show allotropy.
Allotropes of Carbon
It is the purest, hardest form of carbon with high refractive index and density. In it each carbon atom (sp3 hybridised) is tetrahedrally surrounded by four other carbon atoms. It does not conduct electricity as it has no free electrons. It is used in cutting, grinding and drilling instruments and in making jewellery.
It has two dimensional structure, sp2 hybridised carbon atom forms three covalent bonds with three other carbon atoms in the same plane and the 4th electron of each carbon remains free and is responsible for electrical conductivity of graphite. The planar hexagonal rings get fused together to form sheets of one atom thickness. These sheets are held together by weak van der Waals’ forces. These layers can slide over each other and gives softness, greasiness and lubricating property to graphite. It is used in making electrodes, lead pencils and as dry lubricant.
These are the 6nly pure form of carbon. C60 molecule contains 12 five membered rings and 20 six membered rings. The five membered rings are connected to six membered rings while six membered rings are connected to both five and six membered rings. These are used in microscopic ball bearings, light weight batteries, in synthesis of new plastics and new drugs.
- Oxidation States
The common oxidation states are +4 and +2. Carbon also exhibits negative oxidation states, i.e. -4 Down the group, stability of +4 oxidation state decreases and of +2 oxidation state increases due to inert pair effect.
- C02,Si02 and Ge02 are acidic, whereas Sn02 and Pb02 are amphoteric in nature.
Among monoxides, CO is neutral, GeO is distinctly acidic whereas SnO and PbO are amphoteric.
- Monomeric form of C02 is stable due to non availability of d-orbitals. Carbon has tendency to form a multiple bond but Si02 exists in three dimensional polymeric form and has high melting point and is solid at room temperature.
- Reaction with Water
Carbon, silicon and germanium are not affected by water. Tin decomposes with steam to form dioxide and dihydrogen gas.
Lead remains unaffected by water, probably because of a protective oxide film formation.
Some Important Compounds of Group 14 Elements
Some of the important compounds of group 14 elements or carbon family elements are given below :
Water Gas or Synthesis Gas and Producer Gas
Water gas and producer gas are very important industrial fuels.
- The combustion of fossil fuels and decomposition of limestone for cement manufacture, increase the C02 content of the atmosphere. It increases greenhouse effect and raise the temperature of the atmosphere.
- Carbon dioxide can be obtained as a solid in the form of dry ice by allowing the liquefied C02 to expand rapidly. Dry ice is used as a refrigerant for ice-cream and frozen food.
Silicon Tetrachloride SiCl4
- It is tetrahedral and essentially covalent. It is readily hydrolysed by water. It fumes in moist air liberating hydrogen chloride.
- The hydrolysis of SiCl4 occurs due to coordination of OH with empty 3d-orbitals in Si-atom of SiCl4 molecule.
- These are synthetic organosilicon compounds which has repeated unit of R2 SiO.
- These are prepared from alkyl halides.
- Highly cross linked silicone polymer is obtained by the hydrolysis of RSiCl3.
They are used as sealant, greases, electrical insulators and for water proofing of fabrics. Being biocompatible they are also used in surgical and cosmetic plants.
The majority of the compounds consist of silicates, in which silicon and oxygen make giant three dimensional structures.
All silicates involve Si—O bonds of two types :
- Terminal Si—O bonds in which oxygen is bonded to a silicon and not other atom.
- Bridging Si—O—Si bonds in which oxygen is bonded to two silicon atoms.
- The basic building unit of all silicates is the tetrahedral Si04– ion.
Silicates are classified into following types :
- Ortho silicates
- Pyro silicates
- Cyclic silicates
e.g. Wollastonite (Ca3Si309)
Bentonite [BaTi (Si309)]
These are microporous aluminosilicate having general formula
Zeolites are used as molecular seives and can separate molecules of different sizes. They are also used extensively as catalyst.