Bonding and Structure: Practice Questions

The hydronium ion, \(\text{H}_3\text{O}^+\), is formed when an acid dissolves in water. What is the shape and approximate bond angle in the \(\text{H}_3\text{O}^+\) ion?

Which statement correctly explains the trend in boiling temperatures of the noble gases down Group 0?

The Valence Shell Electron Pair Repulsion (VSEPR) theory allows us to predict the geometry of molecules and polyatomic ions by considering the repulsion between electron pairs.
Which of the following species has a square planar molecular geometry?

Which statement correctly explains why metals typically have high melting temperatures and are good conductors of electricity?

The degree of covalent character in an ionic bond can be predicted using Fajan’s rules, which consider the polarizing power of the cation and the polarisability of the anion.
Which of the following anhydrous halides is expected to possess the greatest degree of covalent character?

State the shape and the approximate bond angle around the central carbon atom in a molecule of ethene, \(C_2H_4\).

Using the concept of electronegativity, explain why the bond between hydrogen and chlorine in \( \text{HCl} \) is described as a polar covalent bond rather than a purely ionic or purely covalent bond.

The Born-Haber cycle can be used to determine experimental lattice energies. Explain why the experimental lattice energy for silver iodide (\( \text{AgI} \)) is significantly more exothermic than the value calculated using a purely ionic model, referring to the polarising power of the silver ion.

Ionic bonding involves the electrostatic attraction between oppositely charged ions, while covalent bonding involves the sharing of electron pairs.

(a) Define the term electronegativity. (1 point)
(b) Explain the trend in the melting temperatures of the following Period 3 chlorides in terms of their structure and bonding: \(\text{NaCl}\), \(\text{MgCl}_2\), and \(\text{SiCl}_4\). (3 points)
(c) Use Fajan's rules to explain why aluminum iodide, \(\text{AlI}_3\), shows more covalent character than aluminum fluoride, \(\text{AlF}_3\). (2 points)

The shapes of molecules and ions can be predicted using the Valence Shell Electron Pair Repulsion (VSEPR) theory.

(a) For each of the following species, state the number of bonding pairs and lone pairs of electrons around the central atom, and name the molecular shape:
(i) \(\text{PCl}_5\)
(ii) \(\text{SF}_6\)
(iii) \(\text{ClF}_3\) (3 points)
(b) Predict the bond angles in \(\text{NH}_3\) and \(\text{NH}_4^+\). Explain why the bond angle in \(\text{NH}_3\) is smaller than the bond angle in \(\text{NH}_4^+\). (3 points)
(c) Ammonia reacts with boron trifluoride (\(\text{BF}_3\)) to form the adduct \(\text{H}_3\text{N}\cdot\text{BF}_3\). Describe the type of bond formed between nitrogen and boron and explain how it arises. (2 points)