AP - Advanced Placement Chemical Bonding and Molecular Structure 1

Question 1

What is the molecular geometry and approximate bond angle of XeF₄?

Accepted Answer

Square planar, 90°

Answer

XeF₄ has six electron domains around xenon (4 bonding pairs + 2 lone pairs), producing an octahedral electron geometry. The two lone pairs occupy opposite axial positions, placing all four F atoms in a plane at 90° to one another — a square planar molecular geometry.

Question 2

Which of the following C–O bonds has the shortest bond length?

Accepted Answer

C≡O in CO (bond order 3)

Answer

Bond length decreases as bond order increases between the same pair of atoms. CO has a triple bond (bond order 3), giving it the highest bond order among these species and therefore the shortest C–O distance (~113 pm), shorter than CO₂ (~116 pm), CO₃²⁻ (~129 pm), or CH₃OH (~143 pm).

Question 3

According to molecular orbital theory, what is the bond order of NO and what are its magnetic properties?

Accepted Answer

Bond order = 2.5, paramagnetic

Answer

NO has 11 valence electrons. Filling the MO diagram yields σ2s², σ*2s², σ2p², π2p⁴, π*2p¹. Bond order = (8 bonding − 3 antibonding) ÷ 2 = 2.5. The single unpaired electron in the π*2p orbital makes NO paramagnetic.

Question 4

What is the hybridization of phosphorus in PCl₅ and what molecular geometry results?

Accepted Answer

sp³d; trigonal bipyramidal

Answer

PCl₅ has five bonding pairs and no lone pairs around P, requiring five equivalent hybrid orbitals. Mixing one s, three p, and one d orbital produces sp³d hybridization. This gives a trigonal bipyramidal geometry with 120° equatorial and 180° axial bond angles.

Question 5

Which of the following molecules has a non-zero dipole moment?

Accepted Answer

ClF₃

Answer

ClF₃ adopts a T-shaped geometry with two equatorial lone pairs, creating an asymmetric distribution that prevents bond dipoles from canceling, producing a net dipole. BF₃ (trigonal planar), XeF₄ (square planar), and PF₅ (trigonal bipyramidal) are all highly symmetric, so their bond dipoles cancel exactly.

AP Practice Test

AP Practice Test

AP - Advanced Placement Chemical Bonding and Molecular Structure 1