Question

What is the difference between electron geometry and molecular geometry?

Answer 1

Geometry of any molecule is determined on the basis of postulates proposed by VSEPR (Valence Shell Electron Pair Theory). According to VSEPR theory, the shape of any molecules depends upon the total number of valence electrons present to the central atom.

Complete Step By Step Answer:
VSEPR theory postulates that the shape of any molecules is affected by the presence of lone pair electrons as well as bonded electrons. However, the strength of repulsion between these electrons may vary depending upon their nature.
Some basic difference between molecular geometry and electron geometry are-

PROPERTIES	MOLECULAR GEOMETRY	ELECTRON GEOMETRY
definition	It explains the arrangement of molecules around the central atom.	It explains the arrangement of electron pairs around the central atom.
Location of substituents	It gives the basic idea of location of molecules around the central atom.	It gives the basic idea of location of electrons around the central atom.
Nature of electrons	It is based upon the bonded electron pair in a compound.	It is based upon the bonded electron as well as lone pair electrons present in a compound.
Basic calculation	It includes calculation of bonded electrons around the central atom.	It includes calculation of total valence shell electrons around the central atom.

Example- molecule of methane $C{H_4}$ contains four bonds between carbon atom and hydrogen atom and we already know that valency of carbon is $4$ . Hence, all the valence electrons participate in bond formation and no lone pair electrons are present around the carbon atom. Finally, according to the molecular geometry molecule of $C{H_4}$ oriented in tetrahedral shape.
Example- molecule of ammonia $N{H_3}$ contains three bonds between nitrogen and hydrogen atom and we already know that the outermost shell of nitrogen contains $5$ electrons. Hence, $3$ electrons are used in bond formation and the remaining two electrons present around the nitrogen atom have lone pairs. Finally, according to the electron geometry molecule of $N{H_3}$ oriented in trigonal pyramidal.

Note:
The strength of repulsion of electrons is in order:
lone pair-lone pair $>$ lone pair- bond pair $>$ bond pair – bond pair.
Hence, we can see that repulsion force is maximum in the case of lone pairs, therefore molecules change their geometry to attain stability in its geometry.