Covalent Bonding — Practice · Grade 11 Science

Chapter: Bonding, Formulas & Molecular Structure

What this practice covers

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

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

Vocabulary used: covalent bond, molecule, bonding pair, lone pair, Lewis structure, double bond, triple bond, diatomic molecule.

Problem 1

A covalent bond forms when two atoms…
  1. share electrons
  2. lose electrons
  3. gain protons
  4. transfer electrons
Answer and explanation

share electrons

Covalent bonding is the sharing of one or more pairs of electrons between atoms.

Problem 2

Covalent bonds usually form between…
  1. two metals
  2. a metal and a nonmetal
  3. two nonmetals
  4. two noble gases
Answer and explanation

two nonmetals

Two nonmetals both attract electrons strongly, so they share rather than transfer, forming covalent bonds.

Problem 3

How many electrons are shared in a single covalent bond?
Answer and explanation

2

A single bond is one shared pair, and a pair is 2 electrons.

Problem 4

A nitrogen molecule (N₂) contains a triple bond. How many electrons are shared between the two nitrogen atoms?
Answer and explanation

6

A triple bond is 3 shared pairs, and 3 pairs × 2 electrons = 6 electrons.

Problem 5

Explain why molecular compounds like water tend to have much lower melting points than ionic compounds like salt.
Answer and explanation

In a molecular compound the covalent bonds inside each molecule are strong, but the attractions between separate molecules are weak, so little energy is needed to pull the molecules apart. In an ionic compound every ion is locked to its neighbors by strong electrostatic forces throughout the lattice, so far more energy — a higher temperature — is needed to break it apart.

Problem 6

In the Lewis structure of carbon dioxide (O=C=O), how many lone pairs are on each oxygen atom?
  1. 1
  2. 2
  3. 3
  4. 0
Answer and explanation

2

Each oxygen shares 2 pairs in its double bond and keeps 2 lone pairs of its own, completing its octet.

Problem 7

How many shared electrons are represented by a triple bond? Show the reasoning, not just the conclusion.
Hints

A shared pair is not ownership transferred permanently to only one atom.

Answer and explanation

Six electrons in three shared pairs in the simple bond model.

Problem 8

Why can a covalent molecule be polar even though it is electrically neutral?
Hints

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

Answer and explanation

Partial charge separation can create a net molecular dipole without net charge.

Problem 9

Bond-order comparisons need a matched chemical contextBond-order comparisons need a matched chemical contextSelected C–C bondRelative lengthBonding modelSingleLongerOne shared pairDoubleIntermediateTwo shared pairsTripleShorterThree shared pairsCompare compatible species; energy is not simply pair-count × constant.Resonance and chemical context can change the comparison.
Original qualitative matched C–C comparison; no universal bond-length or bond-energy dataset is asserted.
Interpret the supplied visual. Does a C=C double bond have exactly twice the dissociation energy of every C–C single bond?
Answer and explanation

No. Bond order supports a qualitative comparison for suitable species, but measured energy depends on the full bonding environment and defined process.

Bond order summarizes bonding in a model: a Lewis single, double or triple line commonly represents one, two or three shared pairs. For comparable atom pairs, higher bond order often corresponds to shorter, stronger bonds, but bond energies are not exact integer multiples and depend on the surrounding molecule. Bond dissociation energy concerns a specified bond-breaking process. Delocalized structures can have intermediate effective orders, so a selected Lewis drawing should not be treated as a direct ruler or calorimeter.

No. Bond order supports a qualitative comparison for suitable species, but measured energy depends on the full bonding environment and defined process.

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

Compare CO₂ and H₂O: both have polar bonds. Explain why bond polarity alone cannot establish that both molecules have a net dipole.
Answer and explanation

CO₂ is linear with equal opposing bond contributions that cancel in the ideal symmetric molecule. H₂O is bent, so its bond dipoles do not cancel. Geometry and the full charge distribution matter.

CO₂ is linear with equal opposing bond contributions that cancel in the ideal symmetric molecule. H₂O is bent, so its bond dipoles do not cancel. Geometry and the full charge distribution matter.

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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