Question

How do I determine the bond angle in a molecule?

Answer 1

Hint Bond angle can be defined as the angle formed between two covalent bonds originating from the same atom. Bond angle can also be defined as the geometric angle between any two adjacent covalent bonds. This bond tells us about the molecular geometry of the compound.

Complete answer:
The bond angle generally depends on the number of lone pairs present in an atom. An atom which has no lone pairs shows a shape of trigonal planar shape and in this case bond angle is of $120{}^{\circ }$. The molecule which contains one lone pair which forms a bent shape and bond angle is of $118{}^{\circ }$. On the other hand if a molecule has two lone pairs then it forms a linear shape. For example a compound known as methane which has no lone pairs forms a tetrahedron showing bond angle of $109.5{}^{\circ }$, ammonia has one lone pair have bond angle of $107.5{}^{\circ }$ and forms trigonal pyramidal shape whereas water having two lone pairs of electrons has a bent shape with bond angle of $104.5{}^{\circ }$.
VSEPR theory is basically used to predict the geometry of molecules; this theory assumes that each atom in a molecule will achieve a geometry that minimizes the repulsion between electrons in the valence shell of that atom. Hence in this way we can calculate the bond angle of any molecule

Note: Mainly VSEPR theory tells us about the bonding and molecular geometry of organic molecules and polyatomic ions. It predicts the 3-D shape of the molecule and it can predict the shape of nearly all compounds.