Shapes Of Molecules

The shape of the molecule depends on the number of bonding and non-bonding electron pairs in the outer most shell of the central atom which arrange themselves in such a way that there is a minimum repulsion between them so that molecule has minimum energy so that maximum stability. For example Beryllium chloride(Be Cl₂ ). Be is the central atom and it has two bond pairs of electrons in its outer most shell(Cl-Be-Cl).Therefore its shape is Linear. If the central atom of a molecule is surrounded by only bonding electron pairs(bps) then the geometry(shape) of the molecule is regular. Number of bonding pair of electrons is 2 example(BeCl₂)then shape of the molecule is linear, if 3 example (BCl₃) then triangular planar, if 4 (CH₄) then regular tetrahedral, if 5 (PCl₅) then triangular bipyramidal, and if 6 (SF₆) then regular octahedral.

When the central atom in a molecule is surrounded by both bonding and non bonding pair of electrons, the does not have the regular shape , example: ammonia.

In ammonia, the central atom is Nitrogen. Nitrogen has surrounded by three bond pair of electrons and one lone pair of electrons. The expected shape for ammonia is tetrahedral because of 4 electron pairs but, the shape of ammonia is pyramidal. This is because there is lone pair-bond pair electron repulsion in ammonia along with bond pair-bond pair repulsion.