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CBSE Important Questions

CBSE Guess > Papers > Important Questions > Class X > 2014 > Chemistry > Chemistry By Mrs. Kritika Bhola



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 CnH2n+2

2. 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 --- CnH2n
    Alkenes contain a double bond between two carbon atoms which is formed by sharing of two electron pairs. Simplest alkene is Ethene.

  2. Alkynes --- CnH2n-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.

  3. Alkyl  Groups ---- CnH2n+2
    The group formed by the removal of one hydrogen atom from an alkane molecule .
    Methyl group (CH3-) is formed by the removal of one  H  atom from Methane  (CH4) , etc.

  4. 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 CnH2n

  2. 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 -

1 carbon atom Meth
2 Eth
3 Prop
4 But
5 Pent
6 Hex
7 Hept
8 Oct
9 Non
10 Dec

Single  Bond ane
Double Bond ene
Triple  Bond yne
  • 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.
  • 1st isomer  is called n- pentane (normal)
  • 2nd isomer is called isopentane
  • 3rd isomer is called neopentane

Submitted By Mrs. Kritika Bhola
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