The covalent model: notes and practice questions

Which is the $^{1}H$ NMR spectrum of propanone?

A.

B.

C.

D.

The thiocyanate ion, $SCN^-$, can be represented by several resonance structures. Two possible structures are shown below.

Structure I: $[:\ddot{S}-C \equiv N:]^-$

Structure II: $[:\ddot{S}=C=\ddot{N}:]^-$

Which row correctly identifies the formal charges on S, C, and N for each structure and identifies the more stable structure?

Which sequence lists the following molecules in order of decreasing bond angle?

A. $PH_3$, $SiH_4$, $BF_3$, $CO_2$

B. $CO_2$, $BF_3$, $SiH_4$, $PH_3$

C. $BF_3$, $CO_2$, $PH_3$, $SiH_4$

D. $CO_2$, $SiH_4$, $BF_3$, $PH_3$

The standard enthalpy of hydrogenation of cyclohexene is $-120 \text{ kJ mol}^{-1}$.

$C_6H_{10}(l) + H_2(g) \rightarrow C_6H_{12}(l) \quad \Delta H^{\ominus} = -120 \text{ kJ mol}^{-1}$

Based on this value, what would be the predicted standard enthalpy of hydrogenation for the Kekulé structure of benzene, and what does the experimental value being significantly less exothermic indicate about the stability of benzene?

A. Predicted $\Delta H^{\ominus} = -360 \text{ kJ mol}^{-1}$; Benzene is less stable than the Kekulé structure.

B. Predicted $\Delta H^{\ominus} = -360 \text{ kJ mol}^{-1}$; Benzene is more stable than the Kekulé structure.

C. Predicted $\Delta H^{\ominus} = -240 \text{ kJ mol}^{-1}$; Benzene is less stable than the Kekulé structure.

D. Predicted $\Delta H^{\ominus} = -120 \text{ kJ mol}^{-1}$; Benzene is more stable than the Kekulé structure.

In which of the following molecules do all atoms obey the octet rule?

I. $O_3$

II. $SiCl_4$

III. $XeF_4$

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Which species has a net dipole moment?

A. $BF_3$

B. $SiCl_4$

C. $PCl_3$

D. $PCl_5$

What are the electron domain and molecular geometries of $BrF_5$?

A. Trigonal bipyramidal, T-shaped

B. Octahedral, square planar

C. Octahedral, square pyramidal

D. Trigonal bipyramidal, see-saw

What are the hybridizations of the carbon and oxygen atoms in the ethanoate ion, $CH_3COO^-$?

A. Methyl carbon ($CH_3$): $sp^3$, Carboxylate carbon (COO): $sp^2$, Oxygen atoms: $sp^2$

B. Methyl carbon ($CH_3$): $sp^3$, Carboxylate carbon (COO): $sp^2$, Oxygen atoms: $sp^3$

C. Methyl carbon ($CH_3$): $sp^2$, Carboxylate carbon (COO): $sp^3$, Oxygen atoms: $sp^2$

D. Methyl carbon ($CH_3$): $sp^2$, Carboxylate carbon (COO): $sp^2$, Oxygen atoms: $sp^2$

What is the identity of the ester with the molecular formula $C_4H_8O_2$, which has four peaks in its $^1H$ NMR spectrum with an integration ratio of $1:2:2:3$?

A. Methyl propanoate

B. Ethyl ethanoate

C. Propyl methanoate

D. Isopropyl methanoate

What are the electron domain and molecular geometries of the tellurium tetrachloride molecule, $TeCl_4$?

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A. Trigonal bipyramidal, Seesaw

B. Octahedral, Square planar

C. Trigonal bipyramidal, Tetrahedral

D. Tetrahedral, Tetrahedral

Which statement correctly describes the orbital overlap that forms the carbon-carbon triple bond in ethyne, $C_2H_2$?

A. One $\sigma$-bond from the overlap of two $sp^2$ orbitals and two $\pi$-bonds from the sideways overlap of two pairs of p orbitals.

B. One $\sigma$-bond from the overlap of two $sp$ orbitals and two $\pi$-bonds from the sideways overlap of two pairs of p orbitals.

C. Three $\sigma$-bonds from the overlap of three pairs of $sp$ orbitals.

D. One $\sigma$-bond from the overlap of two $sp$ orbitals and two $\pi$-bonds from the sideways overlap of one pair of p orbitals and one pair of $sp$ orbitals.

Which species contain a coordination bond?

I. $H_3O^+$

II. $CO$

III. $BF_3$

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

What are the electron domain and molecular geometries of sulfur tetrafluoride, $SF_4$?

Electron domain geometry | Molecular geometry

---|---

A. Trigonal bipyramidal | Trigonal bipyramidal

B. Trigonal bipyramidal | See-saw

C. Octahedral | Square planar

D. Tetrahedral | Tetrahedral

Nitrogen ($N_2$) and oxygen ($O_2$) are the two most abundant gases in the Earth's atmosphere. Why are they not classified as greenhouse gases?

A. Their bond vibrations do not involve a change in dipole moment.

B. They are elements with low molar masses.

C. They are transparent to ultraviolet radiation.

D. They do not have any polar covalent bonds.

What is the molecular geometry of the central phosphorus atom in the $[PCl_6]^-$ ion?

A. Trigonal bipyramidal

B. Square planar

C. Octahedral

D. See-saw

In which set do all species contain delocalized electrons?

A. $SO_2$, $C_2H_4$, $C$(diamond)

B. $O_3$, $H_2CO_3$, $C_{60}$

C. $C_6H_6$, $CO_3^{2-}$, $NO_3^-$

D. $CH_3COO^-$, $PO_4^{3-}$, $NH_4^+$

Carbon dioxide, $\text{CO}_2$, acts as a greenhouse gas. Which statement explains why $\text{CO}_2$ absorbs infrared radiation?

A. Asymmetrical stretching and bending vibrations result in a change in dipole moment.

B. Symmetrical stretching vibrations result in a change in dipole moment.

C. Infrared radiation promotes electrons to higher energy levels.

D. The polar bonds give the molecule an overall permanent dipole moment.