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

CHEMISTRY CBSE CLASS X

Homologous Series

A group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH₂ group.

Two adjacent homologous groups differ by 1 carbon atom and 2 hydrogen atoms .

General formula of Alkanes --- C_nH_2n+2

Characteristics of a Homologus Series

1.  All members represented by same general formula.
2. Two adjacent homologues differ by a CH2
3. Difference between molecular masses of any 2 homologues is 14 μ
4. All compounds show similar chemical properties.
5. There is gradual change in their physical properties with increase in molecular masses. (melting , boiling points and densities increase)

Alkenes --- C_nH_2n

Alkynes --- C_nH_2n-2

Functional Groups �

An ‘atom’ or a ‘group of atoms’ which makes a carbon compound reactive and decides its properties.

1. Halo Group :   − X  (X can be  Cl, Br or I)
   Chloro , Bromo and Iodo group ----
   When 1 H atom of an alkane is replaced by a halogen atom, we get Haloalkane.
   Eg. CH₄ → Replace one H by Cl → CH₃Cl
   

   General  formula  is  C_nC_2n+1 –X   (  X  may be Cl ; Br; I  )

   Chloromethane - CH₃Cl   ---- methyl chloride
   Bromomethane - CH₃Br   ---- methyl  bromide
   Chloroethane    -  C₂H₅Cl  ----  ethyl  chloride
   Chloropropane  -  C₃H₇Cl  ----  propyl chloride

2. Alcohol Group :  −OH  ( alcoholic  /  hydroxyl group)
   Alcohol group is made up of  1 oxygen and 1 hydrogen atom joined together.
   1 H atom is replaced by an alkane  by a hydroxyl group ( OH  group)
   CH4  → Replace  1 H by  OH → CH3OH
   
   General formula  is  C_nC_2n+1OH
   Methanol  - CH₃OH  ---- methyl  alcohol
   Ethanol     -  C₂H₅OH ---- ethyl alcohol
   Propanol  -   C₃H₅OH ----  propyl  alcohol
   

Submitted By Mrs. Kritika Bhola
Email Id : [email protected]