Chemical Bonding (College Board AP® Chemistry): Exam Questions

The table below shows the bonds found in different molecules.

Identify which bond is the shortest. Justify your answer in terms of bond order.

The bond energy of a C-H bond in methane (CH₄) is 412 kJ/mol, while the bond energy of an H-F bond in hydrogen fluoride (HF) is 565 kJ/mol.

i) Explain why the H-F bond has a higher bond energy than the C-H bond in terms of atomic structure.

ii) Predict whether the bond length in H-F is longer or shorter than in C-H. Justify your answer.

Compound X has the molecular formula C₄H₈O₂ and exists as a white crystalline solid at room temperature. Compound X has a melting point of 135  ^oC and dissolves well in water. The Lewis diagram of a molecule of compound X is shown below.

Explain the type of bonding present in compound X.

Is the C=O bond in compound X nonpolar covalent, polar covalent, or ionic? Justify your answer.

Predict whether compound X is polar or nonpolar. Justify your answer.

State the approximate bond angle around the carbon atom in the –COOH group. Explain your answer in terms of electron domain geometry.

Identify the strongest intermolecular force between molecules of compound X. Explain how this affects the melting point.

Explain why compound X dissolves readily in water.

Two substances, C₂H₆ (ethane) and CH₃OH (methanol), are both gases at room temperature but exhibit very different physical properties.

Based on electronegativity differences, classify the bond between carbon and hydrogen atoms in C₂H₆ as nonpolar covalent, polar covalent, or ionic. Justify your answer.

Identify the strongest type of intermolecular force between molecules of:

i) C₂H₆

ii) CH₃ OH

Draw a Lewis diagram for a single CH₃OH molecule.

Draw a diagram showing an intermolecular interaction between two methanol (CH₃OH) molecules. Clearly indicate the interaction and partial charges on the relevant atoms.

Explain why the boiling point of CH₃OH is significantly higher than that of C₂H₆. Your answer should refer to the differences in intermolecular forces between the two substances.

Methanol is highly soluble in water, whereas ethane is nearly insoluble. Explain this difference in solubility in terms of molecular polarity and interactions with water.

What is meant by a dipole moment?

Carbon dioxide and water both contain polar bonds.

Identify which molecule has a net dipole moment. Justify your answer in terms of molecular geometry.

The dipole moment of NH₃ is greater than that of NF₃ despite both having a trigonal pyramidal shape.

(i) Explain how the electronegativity of fluorine compared to hydrogen affects the dipole moment of NF₃ and NH₃.

(ii) Explain why the dipole moment of NH₃ is greater than that of NF₃ in terms of electron distribution and molecular polarity.

Compare the bonding in metals and ionic solids in terms of electron behavior and the forces that hold the structure together.

(i) Explain why metals are malleable, whereas ionic solids are brittle, in terms of atomic structure and bonding.

(ii) Describe how the application of an external force affects the structure of a metal compared to an ionic solid.

State Coulomb's law and identify its variables.

Identify which compound, potassium bromide or potassium sulfide, has the stronger electrostatic attraction. Justify your answer in terms of Coulomb’s Law.

The experimental lattice energy of NaCl deviates from Coulomb’s Law predictions.

(i) Explain how polarizability affects the lattice energy of NaCl.

(ii) Explain how partial covalent character contributes to this deviation.