The ideal bond angle for a four-electron system is 109.5o. If all four electron pairs are bonding pairs, the shape of the system is tetrahedral. A bent shape is observed if there are two bonding pairs and two lone pairs.

Table of Three to Six Electron Domains

Electron group geometry is the three-dimensional arrangement of atoms in a molecule. The geometry of a molecule is an important factor that affects the physical and chemical properties of a compound.

In C2H4, if we look into the lewis structure, we will see that there are three bonded pairs of electrons around each carbon and zero lone pair. According to the VSEPR chart, the shape of the ethene molecule is trigonal planar.

The molecular geometry definition in chemistry is the arrangement of atoms in relation to a central atom in three-dimensional space. Electron geometry is the arrangement of electron groups. If all the electron groups are bonded, with no lone pairs, then the electron geometry and molecular geometry are the same.

The key difference between shape and geometry of a molecule is that shape of a molecule is the structure of the molecule excluding the lone pair on the central atom whereas the geometry of a molecule describes the arrangement of lone pair and bond pair electrons around the central atom of the molecule.

Water has 4 regions of electron density around the central oxygen atom (2 bonds and 2 lone pairs). These are arranged in a tetrahedral shape. The resulting molecular shape is bent with an H-O-H angle of 104.5°.

BF3 molecule is planar but NF3 is pyramidal.

but BF3 has resonance structures, and some of them have double bonds.

There are three sigma bonds and one lone-pair around phosphorus atom . Therefore, shape of PH3 is trigonal pyramidal.