SHAPES OF MOLECULES CONTAINING TWO ELECTRON PAIRS, SHAPES OF MOLECULES CONTAINING THREE ELECTRON PAIRS:

 

SHAPES OF MOLECULES CONTAINING TWO ELECTRON PAIRS:

 Two bond pair of electrons without any lone pair of electrons around central atom have linear arrangement because it is the only arrangement in which two bond pairs of electrons have minimum repulsion between them. Bond angle in linear molecules is 180⁰ e.g; Becl₂.

Electron pairs in multiply bond are assumed to occupy the position of one electron pair as in a single covalent  bond e.g;

O=O

            H-C = N

SHAPES OF MOLECULES CONTAINING THREE ELECTRON PAIRS:

 When there are three pairs of electron around the central atom, the bond lie in the same plane at an angle of 120⁰ to one another. This arrangement have maximum separation and maximum repulsion between them. The shape for such molecules is trigonal planar e.g; BF₃.

In case of SO2 molecule, sulpher atom has the central position. It has six electrons in its valence shell out of these two electrons are covalently bonded with one oxygen atom formed double covalent bond, whereas one lone pair is used in making dative covalent bond with other oxygen atom and another lone pair left on sulpher atom. As a rule multiple bonding and dative covalent bonds are consider as single bond in position around central sulpher atom.

As the lone pair occupies more space, it will push the two bonded pairs closer to each other and the angle between two bond pairs becomes less than 120⁰.

SHAPES OF MOLECULES CONTAININGFOUR ELECTRON PAIRS:

             The electrostatic repulsion between four pairs of electrons is minimum when they are present at the corners of a regular tetrahedron. The angles between tetrahedron arranged bonds are 109.5⁰ e.g; methane molecule, CH₄

Due to four pairs of electrons the possible arrangement is tetrahedral. As lone pair occupies more space than bond pair because lone pair bond pair repulsion is more than bond pair – bond pair repulsion. Hence, lone pair push the bond pair more close to each other and bond angle decreases to 107⁰. The electronic configuration of N in ammonia is tetrahedral but the overall geometry (shape_ of the molecule is trigonal pyramidal.