Question

Why bond angle is independent of size of atom ?Explain with example .

Answer 1

    Size of the atom is the distance between the outermost orbit (shell) of valence electrons and the nucleus.

    Usually in a molecule with more than two atoms, there is a central atom. The other atoms are bonded to the central atom. Suppose One orbital each of the central atom bonds with one orbital of the other atoms. Then the average of the angles between the bonding orbitals of the central atom is called the bond angle (of the molecule).  Bond angle also affects the shape of the molecule too.

Bond angle does not depend on the size of the central atom or other atoms. Bond angle is the angle between two bonds ie., lines joining the nuclei. 

Bond angle depends on :
  1. Hybridization type of the orbitals of the central atom.
      sp1 Hybridization :   180 deg. Straightline  CO2
      sp2 hybridization:   120 deg.  Planar geometry   Al Cl3 
      sp3     "               :    109 deg. tetrahedral    CH4

  2. Lone electron pairs (not participating in the bond) on the central atom.
      The lone electron pairs repel the orbitals of the bonding electrons. So the bonds come closer to each other. Hence Bond angle decreases.
      Example:   SO2 . Bond angle is less than predicted due to 1 lone pair.
                       In H2O and SF4 too this happens.

  3. Electronegativity of the central atom.

      If the central atom is more electronegative, it pulls electrons in more. This causes the bonding atoms to distance from each other. Bond angle increases.  If central atom is less electronegative, bond angle is less.

  4. Double bond or triple bond:
      Double bond repels other single bonds a little.  Triple bond repels double and single bonds away a little.