Class X Chemistry: Carbon

CARBON – AN UNIQUE ELEMENT

Atomic No.: 6
Electronic Configuration: 2, 4
Valency: 4

1. Any element having 6 protons in the nucleus is CARBON. The Atomic number of Carbon is 6.

2. Carbon is formed by the fusion of hydrogen atoms inside stars.

3. Carbon has 4 electrons in its valency shell. To attain noble gas configuration, carbon shares these 4 electrons by forming covalent bonds.

4. The compounds of carbon have a 3-dimensional shape as the electron cloud in the four bonds remain far apart by repulsion.

5. Allotropy: Allotropy is the property of an element to exist in more than one physical forms. Physical form which differs in the arrangement of atoms. Elements like tin, carbon, sulphur, phosphorus and oxygen exhibit allotropy.  Diamond, Graphite, and Fullerene are allotropes of Carbon.

allotroph of carbon

6. Carbon with Nitrogen, Oxygen or Hydrogen forms various compounds like carbohydrates, proteins, DNA etc which are building blocks of life. These categories of compounds are organic compounds. Carbon is key to life on Earth. Man is a carbon-based life form.

VERSATILE NATURE OF CARBON

Two factors –

(i) Catenation – Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.

(ii) Tetra-Valency – Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.

COMPOUNDS OF CARBON

1. Organic Compounds – Initially, compounds of carbon could only be obtained from living sources and therefore known as organic compounds. In organic compounds, one or more atoms of carbon are covalently linked to atoms of other elements most commonly Hydrogen, Oxygen or Nitrogen.  Urea is the first compound synthesized in 1828 by Friedrich Wohler. So far, formulae of about 3 million carbon compounds are known.Traditionally Carbonates, carbides, oxides of carbon and Cyanides are considered inorganic compounds.

2. Hydro Carbons – Compounds of Hydrogen and Carbon is a particular category of Organic Compounds which are the source of all fossil fuels. Hydrogen has valency 1 and therefore attach to all of the 4 valency electrons of Carbon by forming covalent bonds (formed by sharing of electrons)

3. Saturated Carbon Compounds – Compounds of carbon, which are linked by only single bonds between the carbon atoms are called saturated compounds. Valencies of all the atoms are satisfied by single bonds between them. Such carbon compounds are called saturated compounds. These compounds are normally not very reactive. Saturated hydrocarbons are known as ALKANE. These are also known as paraffin. Example: Methane, Ethane, Propane, etc.

4. Unsaturated Carbon Compounds – Compounds of carbon having double or triple bonds between their carbon atoms are called unsaturated compounds. They are more reactive than the saturated carbon compounds.

(i) Hydrocarbon with double bond: Hydrocarbons having at least one double bond are known as ALKENE. Example: Ethylene, Propylene, Butylene, etc.

(ii) Hydrocarbon with triple bond: Hydrocarbons having at least one triple bond are known as ALKYNE. Example: Ethyne, Propyne, Butyne, etc.

5. Functional Group – Single atom or group of atoms, that have similar chemical properties are called functional group. For example Halogen group, Carboxyl group, Aldehyde group, etc. These functional groups confer specific properties to the compound, regardless of the length and nature of the carbon chain. The functional group is attached to the carbon chain by replacing one hydrogen atom or atoms.

6. Homologous Series – Series of compounds with same general formula and functional group is known as homologous series. Compounds belonging to the same homologous series show similar properties. Compounds of homologous series differ by -CH2 from their consecutive members. Compounds of same homologous series differ by physical properties with increase or decrease in molecular mass.

COVALENT BONDING

Covalent Bond: A covalent bond is a chemical bond formed by sharing of electron pairs between atoms. The key to understanding covalent bond is Electronegativity – The tendency of an atom or molecule to attract electrons and form bonds. Two atoms with similar electro-negativity will not exchange an electron from their outermost shell. The atoms instead share electrons so their valency shell is filled. Covalent bonds occur between on-metals or between two of the same (or similar) elements.

Properties of Covalent Bonds:

a) States: Covalent compounds exist mostly in gaseous state (hydrogen, oxygen, ammonia) or liquid(bromine) and few as solids (iodine, phosphorus)

b) Melting and Boiling points: Covalent compounds have usually low melting and boiling point as the molecules are held by weak forces. These can easily be overcome by heat.

c) Non-conducting nature: Covalent compounds are poor conductors of electricity as they do dissociate into ions.

d) Solubility: Covalent compounds are not soluble in water(polar solvent). They dissolve in non-polar solvent like carbon tetrachloride, Benzene etc.

e) Isomerism: Covalent bonds are rigid and directional. Therefore, these can give different arrangement of atoms in space. So, a single molecular formula may represent a number of different compounds with different properties. This phenomenon is called ISOMERISM.

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