Unit 2: Structure & Properties — Unit Test

Assessment OF Learning
Graded
Duration: 75 min | Total: /60
K/U
/15
Thinking
/15
Comm.
/15
Applic.
/15
Part A: Knowledge & Understanding [15]
Q1 [3]
Write ground-state electron configurations: (a) S, (b) Cr, (c) Br⁻.
Q2 [3]
For each, give VSEPR shape and bond angle: (a) BF₃, (b) H₂O, (c) PCl₅.
Q3 [4]
Multiple choice — strongest IMF in CH₃OH:
Q4 [5]
State hybridization at the central atom of: H₂O, NH₃, BeCl₂, SF₆, C₂H₂.
Part B: Thinking & Investigation [15]
Q5 [5]
For SO₂: draw Lewis structure (with resonance); state shape, polarity, and hybridization.
Q6 [5]
Compare and predict relative b.p.: CH₃CH₂CH₃ vs CH₃OCH₃ vs CH₃CH₂OH (justify with IMFs).
Q7 [5]
Predict whether NF₃ is polar; justify using shape and bond dipoles.
Part C: Communication [15]
Q8 [5]
Explain the quantum mechanical model in terms of orbitals (s, p, d shapes), Pauli exclusion, and Hund's rule.
Q9 [5]
Explain why ionization energy increases left-to-right across a period but decreases down a group.
Q10 [5]
Compare network covalent (e.g., diamond) and molecular covalent (e.g., I₂) solids — properties and reasons.
Part D: Application [15]
Q11 [5]
Why is water a "universal solvent" for ionic salts? Use IMFs and structure.
Q12 [5]
Geckos cling to walls via van der Waals forces. Explain in terms of London dispersion.
Q13 [5]
Predict whether XeF₄ is polar; give shape, hybridization, and reasoning.
Complete Answer Key

Q1. S: [Ne] 3s²3p⁴; Cr: [Ar] 4s¹3d⁵; Br⁻: [Ar] 4s²3d¹⁰4p⁶ = [Kr].

Q2. BF₃ trigonal planar 120°; H₂O bent ~104.5°; PCl₅ trigonal bipyramidal 120°/90°.

Q3. Hydrogen bonding.

Q4. H₂O sp³; NH₃ sp³; BeCl₂ sp; SF₆ sp³d²; C₂H₂ sp.

Q5. SO₂: bent (AX₂E), sp², polar; resonance between two S=O / S–O structures.

Q6. Propane (London only) < dimethyl ether (dipole) < ethanol (H-bond). Ranks: −42, −24, 78 °C.

Q7. NF₃ trigonal pyramidal; bond dipoles + lone pair give net dipole — polar (small dipole, but nonzero).

Q8. Orbitals are probability regions: s spherical, p dumbbell, d cloverleaf. Pauli: max 2 e⁻/orbital, opposite spins. Hund: fill degenerate orbitals singly first.

Q9. Across: Zeff ↑, radius ↓ → IE ↑. Down: shell number ↑ + shielding → IE ↓.

Q10. Network: very high m.p., hard, insulator (diamond). Molecular: low m.p., soft, weak London (I₂). Difference: covalent network throughout vs discrete molecules.

Q11. Water's polar H-bonding network solvates ions via ion–dipole forces.

Q12. Many tiny gecko foot setae produce huge cumulative London dispersion contact area.

Q13. XeF₄: square planar (AX₄E₂), sp³d²; nonpolar — symmetric, dipoles cancel.