Which species has bond angles of 90°?

A. AlCl₄^-

B. $\text{I}$Cl₄^-

C. NH₄⁺

D. SiCl₄

B

What is the hybridization of the numbered atoms in ethanoic acid?

D

Which combination describes the PH₄⁺ ion?

A

What is the hybridization state and electron domain geometry around the circled C, N and O atoms?

A

What is the hybridization of nitrogen and chlorine in NCl₃?

D

Which combination correctly describes the geometry of ${{\mathrm{BrF}}_4}^{-}$?

C

Identifying correct electron domain and molecular geometries around a central atom was answered well by the better candidates. This had the highest discrimination index of all the questions.

Which contain delocalised electrons?

I.   C₆H₅OH
II.  CH₃COO⁻
III. CO₃²⁻

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

D

Which overlap of atomic orbitals leads to the formation of only a sigma (σ) bond?

       I.     s − p

       II.     p − p

       III.     s − s

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

B

In which compound are all carbon atoms sp³ hybridized?

A.  C₂H₂

B.  C₂H₂Cl₂

C.  C₂Cl₄

D.  C₂Cl₆

D

76% of candidates correctly identified the organic compound in which all carbon atoms were sp² hybridized.

Which species have resonance structures?

I.     Ozone, O₃
II.     Carbon dioxide, CO₂
III.     Benzene, C₆H₆

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

B

What is the number of sigma (σ) and pi (π) bonds in the molecule (NC)₂C=C(CN)₂?

A

Which combination describes the bonding and structure in benzoic acid, C₆H₅COOH?

B

In which series are all carbon atoms sp² hybridized?

A.  C₂H₂     H₂CO        HCOOH

B.  C₂H₄     H₂CO        HCOOH

C.  C₂H₂     CO           HCN

D.  C₂H₆     CH₃OH     CH₃OCH₃

B

Which does not show resonance?

A.     PO₄^3–

B.     C₆H₆

C.     C₆H₁₂

D.     O₃

C

Which statement is correct?

A.     Sigma bonds are formed only by the combination of s atomic orbitals.

B.     Pi bonds can be formed in the absence of sigma bonds.

C.     Pi bonds are formed parallel to the axis between atoms.

D.     Pi bonds are formed only by the combination of hybrid orbitals.

C

Which can be represented with only one Lewis structure?

A.     CH₂O

B.     C₆H₆

C.     O₃

D.     NO₃⁻

A

How many sigma (σ) and pi (π) bonds are present in this molecule?

C

Which species has a square planar molecular geometry?

A. SF₄

B. XeF₄

C. CF₄

D. PF₄⁺

B

This was a highly discriminating question. 67 % of the candidates identified the species that has a square planar molecular geometry. One teacher commented that this was a difficult recall question. However, the intention here is not to memorize shapes but rather to use VSEPR theory to deduce the shape.

Which molecule has an expanded octet?

A.     CO

B.     CO₂

C.     SF₂

D.     SF₄

D

Which molecules contain two pi ($\mathrm{\pi }$) bonds?

I.   HCN
II.  H₂CO₃
III. H₂C₂O₄

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

B

Which molecules have at least one sp² hybridized atom?

        I.     CH₃COOH

        II.     CH₃COCH₃

        III.     CH₂CHCH₂OH

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

D

Which atom does not obey the octet rule?

A.  C in CO₂

B.  F in BF₃

C.  O in H₂O

D.  S in SF₆

D

How many sigma (σ) and pi (π) bonds are present in hydrogen cyanide, HCN?

B

89 % of the candidates deduced the numbers of sigma and pi bonds in HCN correctly. The most commonly chosen distractor (C) had the correct number of sigma bonds but only one pi bond.

Which species has delocalized electrons?

A. OH⁻

B. H₂CO

C. CO₂

D. CO₃²⁻

D

This question on delocalized electrons was also well answered.

Which atom is sp² hybridized?

A.  C in H₂CO

B.  C in CO₂

C.  N in CH₃NH₂

D.  O in H₂O

A

What is the hybridization of the circled carbon, oxygen and nitrogen atoms?

D

What is the electron domain geometry of Si in SiO₂?

A.  bent

B.  linear

C.  square planar

D.  tetrahedral

D

How many carbon atoms are sp³, sp² and sp hybridized in the molecule?

A

Identify carbons with sp, sp² , and sp³ hybridization was well answered.

What is the hybridization of carbon and oxygen in methanol?

A

77 % of the candidates deduced the hydridization of carbon and oxygen in methanal. A teacher commented that it was unusual to ask for the hydridization of oxygen, however, this is a reasonable application of the concept.

What is the molecular geometry of SF₄?

A.  Tetrahedral

B.  Trigonal bipyramidal

C.  See-saw

D.  Square planar

C

54% of the candidates deduced the molecular geometry of SF₄. The distractors were chosen with equal frequency by the rest of the candidates. This question discriminated well between high-scoring and low-scoring candidates.

What is the formal charge of the oxygen atom in H₃O⁺?

A.  −2

B.  −1

C.  0

D.  +1

D

44% of candidates were able to determine the formal charge of the oxygen atom in H₃O⁺. The most commonly chosen distractor was -2 (the oxidation state of the oxygen).