Ionic Bonding — Practice · Grade 11 Science

Chapter: Bonding, Formulas & Molecular Structure

What this practice covers

By the end of Ionic Bonding you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: ionic bond, ion, cation, anion, octet rule, crystal lattice, formula unit, polyatomic ion.

Problem 1

Which type of element usually forms a cation by losing electrons?
  1. a halogen
  2. a metal
  3. a nonmetal
  4. a noble gas
Answer and explanation

a metal

Metals hold their few valence electrons loosely and lose them to become positive cations.

Problem 2

When a chlorine atom gains one electron, the ion it forms is called…
  1. a molecule
  2. a cation
  3. an anion
  4. a proton
Answer and explanation

an anion

Gaining an electron gives the atom a negative charge, making it an anion (Cl⁻).

Problem 3

Aluminum forms Al³⁺ and oxygen forms O²⁻. In the neutral compound aluminum oxide, how many oxide ions combine with every 2 aluminum ions?
Answer and explanation

3

Two Al³⁺ give +6, so you need three O²⁻ (−2 each) to reach −6 and balance the charge: Al₂O₃.

Problem 4

Why does solid table salt (NaCl) NOT conduct electricity, while molten NaCl does?
  1. Solid salt contains no charged particles
  2. Electrons flow easily through solid salt
  3. Melting adds extra electrons to the salt
  4. The ions are locked in place in the solid lattice but are free to move when molten
Answer and explanation

The ions are locked in place in the solid lattice but are free to move when molten

Conduction needs mobile charges; the lattice freezes the ions in place, but melting frees them to move and carry current.

Problem 5

Explain, in terms of electrons, why a sodium atom and a chlorine atom form an ionic bond.
Answer and explanation

Sodium has 1 valence electron and chlorine has 7. Sodium transfers its single electron to chlorine, so both reach a full outer shell. Sodium becomes Na⁺ and chlorine becomes Cl⁻, and the opposite charges attract to form the ionic bond.

Problem 6

An ion with a 3+ charge combines with an ion with a 2− charge. Using the criss-cross rule, how many ions in total (cations plus anions) are in one formula unit of the compound?
Answer and explanation

5

Balancing +3 and −2 needs 2 cations (+6) and 3 anions (−6), so one formula unit has 2 + 3 = 5 ions.

Problem 7

Find the neutral formula from Ca²⁺ and Cl⁻. Show the reasoning, not just the conclusion.
Hints

Ionic formulas give ratios in a lattice, not necessarily individual molecules.

Answer and explanation

CaCl₂, because +2 balances two −1 charges.

Problem 8

Why can molten sodium chloride conduct while its solid usually cannot?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Mobile ions carry charge in the melt; ions are constrained in the solid lattice under ordinary conditions.

Problem 9

Conductivity depends on movable charge, not merely charged speciesConductivity depends on movable charge, not merely charged speciesSolidMolten / dissolvedCharge carriers must be mobile for sustained conduction.+−+−+−+−−+
Original qualitative mobility comparison; arrows indicate possible ion motion, not a specific voltage polarity or measured conductivity.
Interpret the supplied visual. Why can a salt solution conduct even though an intact salt crystal usually conducts poorly?
Answer and explanation

Dissolved ions can move through the solution; lattice-bound ions in the ordinary solid are far less mobile.

A solid ionic crystal contains charged ions, but their positions are constrained by the lattice and they do not provide ordinary bulk ionic conduction. Melting or dissolving can make ions mobile, allowing them to carry current under suitable conditions. This does not mean every ionic compound dissolves readily or that solid conductivity is mathematically zero under all conditions. Identify phase, temperature, concentration and the relevant charge carrier before interpreting a conductivity comparison.

Dissolved ions can move through the solution; lattice-bound ions in the ordinary solid are far less mobile.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the chemistry relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 10

Al³⁺ combines with O²⁻. Find the simplest neutral formula and explain why it is not a five-ion molecule drawing for the solid.
Answer and explanation

The least common charge magnitude is 6: two Al³⁺ and three O²⁻ give +6−6=0, so Al₂O₃. The formula states a stoichiometric ratio in an extended solid, not a claim of isolated five-ion molecules.

The least common charge magnitude is 6: two Al³⁺ and three O²⁻ give +6−6=0, so Al₂O₃. The formula states a stoichiometric ratio in an extended solid, not a claim of isolated five-ion molecules.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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