Level 1 — RecognitionChemical Bonding

Chemical Bonding

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1: Recognition (MCQ + Matching + True/False with Justification)

Time limit: 20 minutes
Total marks: 30

Section A — Multiple Choice (1 mark each) — 12 marks

Choose the single best answer.

Q1. Which species is an odd-electron (free radical) molecule?

(a) $CO_2$ (b) $NO$ (c) $N_2$ (d) $H_2O$

Q2. Which molecule shows an incomplete octet on the central atom?

(a) $NH_3$ (b) $BF_3$ (c) $CH_4$ (d) $PCl_3$

Q3. The hybridization of sulfur in $SF_6$ is:

(a) $sp^3$ (b) $sp^3d$ (c) $sp^3d^2$ (d) $sp^2$

Q4. According to VSEPR, the shape of $H_2O$ is:

(a) linear (b) bent (c) trigonal planar (d) tetrahedral

Q5. The bond order of $N_2$ from MOT is:

(a) 1 (b) 2 (c) 3 (d) 2.5

Q6. Which molecule is non-polar despite having polar bonds?

(a) $H_2O$ (b) $NH_3$ (c) $CO_2$ (d) $HCl$

Q7. According to Fajan's rules, covalent character is greatest for:

(a) large cation, large anion (b) small cation, large anion
(c) small cation, small anion (d) large cation, small anion

Q8. $O_2$ is paramagnetic because MOT predicts:

(a) all electrons paired (b) two unpaired electrons in $\pi^*$ orbitals
(c) bond order zero (d) an expanded octet

Q9. The correct expression for dipole moment is:

(a) $\mu = q/d$ (b) $\mu = q \cdot d$ (c) $\mu = d/q$ (d) $\mu = q + d$

Q10. Which involves the weakest intermolecular force?

(a) $H_2O$ (H-bonding) (b) $HCl$ (dipole–dipole)
(c) $Ar$ (London dispersion) (d) NaCl (ionic)

Q11. In the Born–Haber cycle, lattice energy corresponds to:

(a) sublimation of the metal (b) formation of gaseous ions into the crystal lattice
(c) ionization of the metal (d) electron affinity of the non-metal

Q12. A $\sigma$ bond compared to a $\pi$ bond generally has:

(a) weaker overlap (b) sideways overlap
(c) greater overlap along the internuclear axis (d) no overlap

Section B — Matching (1 mark each pair) — 6 marks

Q13. Match the molecule to its geometry.

Column A	Column B
(i) $BeCl_2$	(P) octahedral
(ii) $BF_3$	(Q) linear
(iii) $CH_4$	(R) trigonal planar
(iv) $PCl_5$	(S) tetrahedral
(v) $SF_6$	(T) trigonal bipyramidal
(vi) $NH_3$	(U) trigonal pyramidal

Section C — True/False WITH Justification (2 marks each: 1 T/F, 1 reason) — 12 marks

Q14. Benzene has alternating single and double bonds of unequal length. (T/F + justify)

Q15. $He_2$ does not exist as a stable molecule. (T/F + justify)

Q16. Ice is less dense than liquid water because of hydrogen bonding. (T/F + justify)

Q17. The best resonance structure has formal charges as close to zero as possible. (T/F + justify)

Q18. Metallic bonding is best described by a fixed pair of shared electrons between two atoms. (T/F + justify)

Q19. $NO$ has a bond order of 2.5. (T/F + justify)

Answer keyMark scheme & solutions

Section A (1 mark each)

Q1. (b) $NO$ — has 11 valence electrons (odd), one unpaired electron. (1)

Q2. (b) $BF_3$ — B has only 6 electrons around it (incomplete octet). (1)

Q3. (c) $sp^3d^2$ — 6 bond pairs → 6 hybrid orbitals → octahedral. (1)

Q4. (b) bent — 2 bond pairs + 2 lone pairs; lone pairs bend the molecule (~104.5°). (1)

Q5. (c) 3 — Bond order $= (8-2)/2 = 3$ ; triple bond. (1)

Q6. (c) $CO_2$ — linear; two equal, opposite bond dipoles cancel → net $\mu = 0$ . (1)

Q7. (b) small cation, large anion — high polarizing power + high polarizability → most covalent character. (1)

Q8. (b) two unpaired electrons in $\pi^*$ orbitals — $\pi^*_{2px}$ and $\pi^*_{2py}$ each singly filled. (1)

Q9. (b) $\mu = q \cdot d$ (1)

Q10. (c) $Ar$ (London dispersion) — weakest of the listed forces (noble gas, only induced dipoles). (1)

Q11. (b) formation of gaseous ions into the crystal lattice (1)

Q12. (c) greater overlap along the internuclear axis — head-on overlap → stronger. (1)

Section B (Q13, 1 mark each correct pair) — 6 marks

Molecule	Geometry
(i) $BeCl_2$	(Q) linear
(ii) $BF_3$	(R) trigonal planar
(iii) $CH_4$	(S) tetrahedral
(iv) $PCl_5$	(T) trigonal bipyramidal
(v) $SF_6$	(P) octahedral
(vi) $NH_3$	(U) trigonal pyramidal

Award 1 mark per correct match, max 6.

Section C (2 marks each: 1 for T/F, 1 for justification)

Q14. FALSE. (1) Benzene has delocalized π electrons; all six C–C bonds are equal in length (~139 pm), intermediate between single and double. (1)

Q15. TRUE. (1) MO config gives bond order $= (2-2)/2 = 0$ ; no net bonding → not stable. (1)

Q16. TRUE. (1) In ice, H-bonds hold water molecules in an open hexagonal lattice with more empty space, lowering density below that of liquid water. (1)

Q17. TRUE. (1) Structures with minimal (near-zero) formal charges, and negative formal charge on the more electronegative atom, are most stable and contribute most. (1)

Q18. FALSE. (1) Metallic bonding is described by the electron-sea / delocalized model (or band theory): valence electrons are free-moving over all cations, not localized between two atoms. (1)

Q19. TRUE. (1) $NO$ has 11 valence electrons; bond order $= (8-3)/2 = 2.5$ . (1)

[
  {"claim":"N2 bond order = 3","code":"bond_order = (8-2)/2; result = (bond_order == 3)"},
  {"claim":"O2 bond order = 2 with 2 unpaired electrons","code":"bond_order = (8-4)/2; unpaired = 2; result = (bond_order == 2 and unpaired == 2)"},
  {"claim":"He2 bond order = 0","code":"bond_order = (2-2)/2; result = (bond_order == 0)"},
  {"claim":"NO bond order = 2.5","code":"bond_order = (8-3)/2; result = (bond_order == 2.5)"}
]