Question

Why does ${\mathrm{NH}}_3$ have a larger bond angle than ${\mathrm{PH}}_3$?

Answer 1

${\mathrm{NH}}_3$:

• In the outermost shell of N in ${\mathrm{NH}}_3$, there are 4 electron pairs—3 bonding pairs and 1 lone pair.
• The bond angle depends on the main factor that is electronegativity.
• Since N is more electronegative than P so, it will attract hydrogen more strongly than P,
• So, the bond length between ${\mathrm{NH}}_3$ is shorter.
• Hence the bond angle of ${\mathrm{NH}}_3$ is $107°$.

${\mathrm{PH}}_3$:

• The size and number of p orbitals are higher for Phosphorus (2p vs 3p) as compared to ${\mathrm{NH}}_3$,
• Because of that there is less overlapping between the orbitals of Hydrogen and Phosphorus.
• The bond angle depends upon the significant factor which is electronegativity.
• Phosphorus has less electronegativity than Nitrogen, because of that the electrons will attract towards Nitrogen
• Hence, the Bond angle of ${\mathrm{PH}}_3$ is $91°$.

In ${\mathrm{NH}}_3$, the shared pair of electrons are drawn to the centre atom because it is more electronegative. Because of the electron-electron repulsion force, they are strongly repulsed.

Hence, ${\mathrm{NH}}_3$ have a larger bond angle than ${\mathrm{PH}}_3$ because of larger bond angle and high electronegativity in case of ${\mathrm{NH}}_3$, so it attracts more electrons towards itself.

Therefore, the bond angle of ${\mathrm{NH}}_3$ is $107°$ where as the bond angle of ${\mathrm{PH}}_3$ is $91°$