Number of compounds/species from the following with non-zero dipole moment is ______
\(\text{BeCl}_2, \, \text{BCl}_3, \, \text{NF}_3, \, \text{XeF}_4, \, \text{CCl}_4, \, \text{H}_2\text{O}, \, \text{H}_2\text{S}, \, \text{HBr}, \, \text{CO}_2, \, \text{H}_2, \, \text{HCl}\)
\(\text{BeCl}_2, \, \text{BCl}_3, \, \text{NF}_3, \, \text{XeF}_4, \, \text{CCl}_4, \, \text{H}_2\text{O}, \, \text{H}_2\text{S}, \, \text{HBr}, \, \text{CO}_2, \, \text{H}_2, \, \text{HCl}\)
Correct Answer: 5
Approach Solution - 1
Among the given molecules:
Polar molecules with non-zero dipole moment (\(\mu \neq 0\)): NF\(_3\), H\(_2\)O, H\(_2\)S, HBr, HCl.
Non-polar molecules with zero dipole moment (\(\mu = 0\)): BeCl\(_2\), BCl\(_3\), XeF\(_4\), CCl\(_4\), CO\(_2\), H\(_2\).
Approach Solution -2
The dipole moment of a molecule depends on two factors:
1. The polarity of individual bonds (difference in electronegativity between atoms).
2. The geometry (shape) of the molecule, which determines whether individual bond dipoles cancel or add up.
A molecule has a non-zero dipole moment if the vector sum of all bond dipoles ≠ 0.
Step 2: Analyze each species
(1) BeCl₂
Linear molecule (Cl–Be–Cl) with equal bond dipoles in opposite directions → dipoles cancel.
μ = 0
(2) BCl₃
Trigonal planar geometry with three equal B–Cl bonds symmetrically arranged → dipoles cancel.
μ = 0
(3) NF₃
Trigonal pyramidal shape (due to one lone pair on N). Bond dipoles do not cancel completely.
μ ≠ 0
(4) XeF₄
Square planar geometry with symmetric arrangement of bonds → dipoles cancel.
μ = 0
(5) CCl₄
Tetrahedral geometry with four equal bonds → perfectly symmetrical → dipoles cancel.
μ = 0
(6) H₂O
Bent (angular) molecule with two lone pairs on oxygen → resultant dipole moment present.
μ ≠ 0
(7) H₂S
Bent shape like H₂O (though less polar), but still has a resultant dipole moment.
μ ≠ 0
(8) HBr
Diatomic molecule of different atoms → polar bond → non-zero dipole moment.
μ ≠ 0
(9) CO₂
Linear O=C=O, bond dipoles cancel each other → no net dipole.
μ = 0
(10) H₂
H–H is nonpolar (same atoms) → no dipole moment.
μ = 0
(11) HCl
Diatomic molecule of different atoms → polar bond → non-zero dipole moment.
μ ≠ 0
Step 3: Count species with non-zero dipole moment
Molecules with non-zero dipole moment are:
NF₃, H₂O, H₂S, HBr, HCl → 5 molecules.
Final answer
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