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Chemistry

Carbon and Its Compounds

HYDROCARBONS

A compound made up of hydrogen and carbon only . Natural source is petroleum.
Two types--  Saturated ; unsaturated

1. Saturated  Hydrocarbons  (Alkanes)-

 Carbon atoms are connected with single covalent bonds and end with ‘ane’. They are unreactive.
The general formula is C_nH_2n+2

1. Unsaturated  Hydrocarbons ( Alkenes  and Alkynes) -

 Carbon atoms are connected by a ‘double bond’ or a ‘triple bond’ .These are obtained mostly from petroleum by a process called cracking.

1. Alkenes ---  C_nH_2n

Alkenes contain a double bond between two carbon atoms which is formed by sharing of two electron pairs. Simplest alkene is Ethene.

1. Alkynes --- C_nH_2n-2

Alkynes contain a triple bond between two carbon atoms which is formed by sharing of three electron pairs. Simplest Alkyne is Ethyne whose common name is Acetylene.

Alkyl  Groups ---- C_nH_2n+1

The group formed by the removal of one hydrogen atom from an alkane molecule .
Methyl group (CH^3- ) is formed by the removal of one  H  atom from Methane  (CH₄) , etc.

Cyclic  Hydrocarbons

Hydrocarbons in which the carbon atoms are arranged in the form of a ring. They may be saturated or unsaturated.

1. A saturated cyclic hydrocarbon is ‘cyclohexane’ –  C₆H₁₂

Electron dot structure is obtained by putting two electron dots in place of every single bond in its structural formula.

Cyclopropane - C₃H₆

Cyclobutane – C₄H₈

Cyclopentane - C₅H₁₀

General formula of cycloalkanes  is C_nH_2n

1. An unsaturated cyclic hydrocarbon is ‘ benzene’ ( aromatic  compounds ) whose electron dot structure is  --  2 electrons in place of every single bond and 4 electrons in place of every double bond in its structural formula.

Single  bond  --  2 shared electrons
Double bond  --  4 shared electrons

Naming Hydrocarbons ---

 Isomers :- The organic compounds having the same molecular formula but different structures.

• Normal butane has a straight line structure whereas iso-butane structure has a branched chain structure.
• Isomerism is possible only with hydrocarbons having 4 or more carbon atoms ie. Isomerim is not possible in methane, ethane and propane.
• 1^st isomer  is called n- pentane (normal)
• 2^nd isomer is called isopentane
• 3^rd isomer is called neopentane

Submitted By Mrs. Kritika Bhola
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