Explain the dipole moment of a triatomic molecule $(AB_2)$.

(N/A) Triatomic molecules $(AB_2)$ can be classified into two types based on their geometry and dipole moment:
| Feature | Linear $AB_2$ molecules | Angular $AB_2$ molecules |
| :--- | :--- | :--- |
| $(i)$ Structure | $B-A-B$ | $A$ with lone pairs bonded to two $B$ atoms |
| $(ii)$ Lone pair on $A$ | Not present | Present |
| $(iii)$ Examples | $CO_2, CS_2, BeH_2, BeCl_2, BeF_2$ | $H_2O, NO_2, H_2S, F_2O$ |
| $(iv)$ Dipole moment | $\mu = 0$ $D$ (Non-polar) | $\mu \neq 0$ $D$ (Polar) |
In linear $AB_2$ molecules,the two equal bond dipoles point in opposite directions and cancel each other's effect,resulting in a net dipole moment of zero. In angular $AB_2$ molecules,the presence of lone pairs on the central atom $A$ results in a bent geometry,preventing the bond dipoles from cancelling out,thus making the molecule polar.