Free Dipole Moment MCQs with Answers

1. A molecule is polar only if it contains polar bonds and

• A. has an even number of atoms
• B. contains at least one lone pair
• C. the individual bond dipoles do not cancel because of the molecular shape
• D. contains hydrogen

Explanation: Carbon dioxide has two strongly polar bonds but is linear, so the two dipoles point in opposite directions and cancel, leaving a non polar molecule with zero dipole moment. Water has similar bonds but is bent, so its dipoles add and the molecule is strongly polar. Shape therefore decides polarity just as much as electronegativity difference does.

2. Which of the following molecules has a zero dipole moment?

• A. H2O
• B. NH3
• C. HCl
• D. CCl4

Explanation: Tetrachloromethane has four polar carbon to chlorine bonds arranged symmetrically about the central carbon, so the four dipoles cancel exactly and the molecule is non polar overall. Water and ammonia are bent and pyramidal respectively, so their dipoles reinforce, and hydrogen chloride is a simple polar diatomic. Symmetry is the property to look for in this type of question.

3. Dipole moment is measured in

• A. debye units
• B. joules
• C. angstroms
• D. moles

Explanation: Dipole moment is the product of the magnitude of the separated charge and the distance between the centres of charge, and it is quoted in debye, with water at about 1.85 D. A larger value means a more polar molecule and therefore stronger dipole to dipole attraction and a higher boiling point. Angstroms measure length and joules measure energy, so neither can express this quantity.

4. The percentage ionic character of a covalent bond increases as

• A. the two atoms become more similar
• B. the electronegativity difference between the two atoms increases
• C. the bond becomes shorter
• D. the temperature rises

Explanation: The greater the electronegativity difference, the more unequally the pair is shared, until at a difference of roughly 1.7 the bond is regarded as more ionic than covalent. Hydrogen fluoride is highly polar for this reason while hydrogen iodide is nearly non polar. This makes the covalent and ionic extremes two ends of a continuous scale rather than separate categories.

5. An ionic bond is formed by

• A. the sharing of a pair of electrons between two atoms
• B. the complete transfer of electrons from a metal to a non metal
• C. the overlap of two half filled orbitals
• D. the delocalisation of electrons over a lattice of cations

Explanation: Transfer produces oppositely charged ions held by electrostatic attraction, which is why ionic compounds have high melting points and conduct when molten. Sharing gives a covalent bond and delocalisation gives metallic bonding. Ionic character increases as the electronegativity difference between the two atoms widens.

6. The bond in a hydrogen chloride molecule is

• A. purely ionic
• B. polar covalent, with the shared pair drawn towards chlorine
• C. non polar covalent
• D. metallic

Explanation: Chlorine is more electronegative than hydrogen, so the shared electrons sit closer to it, giving chlorine a partial negative charge and hydrogen a partial positive one. The electronegativity difference is not large enough for complete transfer, so the bond is polar rather than ionic. This polarity is why hydrogen chloride dissolves readily in water and ionises there.

7. The dipole moment of a molecule of carbon tetrachloride is zero because

• A. the carbon to chlorine bonds are non polar
• B. the four polar bonds are arranged symmetrically so their dipoles cancel
• C. chlorine and carbon have the same electronegativity
• D. the molecule is planar

Explanation: Each bond carries a substantial dipole, but the tetrahedral symmetry means the four vectors sum to zero, leaving the molecule non polar overall. Replacing one chlorine with hydrogen destroys the symmetry and gives chloroform a measurable dipole moment. Shape therefore matters as much as bond polarity in deciding whether a molecule is polar.

8. Which molecule contains a bond with the greatest ionic character?

• A. HF
• B. HCl
• C. HBr
• D. HI

Explanation: Fluorine is the most electronegative element, so the difference from hydrogen is largest in hydrogen fluoride and the shared pair is most unevenly distributed. Ionic character therefore falls down the group as the halogen becomes less electronegative. This trend also explains why hydrogen fluoride is the only one of the four that hydrogen bonds strongly.

9. Metallic bonding is best described as

• A. the sharing of electrons between two adjacent atoms
• B. the attraction between a lattice of positive ions and a sea of delocalised electrons
• C. the transfer of electrons from one metal atom to another
• D. hydrogen bonding between metal atoms

Explanation: The valence electrons are free to move throughout the whole structure, which accounts for electrical and thermal conductivity, lustre and the ability of the metal to be hammered into shape without shattering. Because the bonding is non directional, layers of ions can slide without breaking the structure. Strength increases with the number of delocalised electrons per atom.

10. The forces holding molecules of iodine together in the solid state are

• A. covalent bonds
• B. ionic bonds
• C. London dispersion forces
• D. hydrogen bonds

Explanation: Iodine molecules are non polar, so the only attraction available is the temporary induced dipole force, which nonetheless grows large enough in such a heavy molecule to make iodine a solid at room temperature. The strong covalent bond inside each molecule is not broken when the solid sublimes. This distinction between intramolecular and intermolecular forces is the point of the question.