CAIE A-Level Chemistry Covalent Bonding: Definition

A covalent bond is a shared pair of electrons between atoms. For CAIE A-Level Chemistry, the stronger definition adds the reason the bond holds: electrostatic attraction between the shared pair of electrons and the nuclei of the bonded atoms.

That wording matters because exam questions often reward precision, not just the phrase "sharing electrons".

Quick Answer

What a Covalent Bond Means

The shared pair of electrons is attracted to both positive nuclei. This attraction holds the atoms together. That is why a complete A-Level answer should mention the shared pair and the attraction to nuclei.

Weak wording:

A covalent bond is when atoms share electrons.

Stronger wording:

A covalent bond is the electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Markscheme Translation: How the Definition Gets Marks

For a 2-mark definition question, the marks often split like this:

This is why the phrase "atoms share electrons" can be too loose. It may describe the idea, but it does not always include the attraction that holds the bond together.

Dot-and-Cross Diagrams

Dot-and-cross diagrams show which atom each outer-shell electron comes from. They do not mean the electrons stay different after bonding; they are a drawing convention to make the sharing visible.

For simple molecules, check:

• the number of outer-shell electrons
• which electrons are shared
• which electrons remain as lone pairs
• whether each atom has a stable outer shell where expected

Exam-Style Worked Example

Question: Define a covalent bond.

Worked answer:
A covalent bond is the electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Why this earns marks:
The answer includes the shared pair and the attraction to nuclei. It is more precise than saying "two atoms share electrons" because it explains what the bond is.

Common Mistakes

Mini Practice Set

Practice This Topic

Try this exam-style question:
Define a covalent bond and explain why the shared pair of electrons is attracted to both nuclei.

Answer guide:

• A covalent bond involves a shared pair of electrons.
• The shared pair is attracted electrostatically to both positive nuclei.
• This attraction holds the atoms together.
• Use dot-and-cross diagrams to show which outer-shell electrons are shared.

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Related Study Links

• Explore the course Study Hub
• A-Level Chemistry Bonding: Covalent Bonds and Intermolecular Forces
• CAIE AS Chemistry Atomic Structure Guide
• CAIE AS Chemistry Group 2 Trends Guide
• A-Level Chemistry Organic Mechanisms Guide
• CAIE A-Level Chemistry AS Question Bank

FAQ

What is a covalent bond?

A covalent bond is a shared pair of electrons between atoms. For CAIE A-Level Chemistry, a stronger definition says it is the electrostatic attraction between the shared pair of electrons and the nuclei of the bonded atoms. This extra attraction wording is often what separates a vague answer from a mark-worthy one.

How many marks is a covalent bond definition usually worth?

A covalent bond definition can reward two separate ideas: the shared pair of electrons and the electrostatic attraction to the nuclei. If you only write that atoms share electrons, the answer may be incomplete. A safer 2-mark answer includes both the shared pair and the attraction holding the atoms together.

What is a dot-and-cross diagram?

A dot-and-cross diagram shows outer-shell electrons using different symbols for different atoms. It helps you show which electrons are shared in covalent bonds and which remain as lone pairs. The dots and crosses are a drawing convention, not a claim that the electrons behave differently after bonding.

Is covalent bonding electron transfer?

No. Covalent bonding is not electron transfer; it involves atoms sharing pairs of electrons. Electron transfer is associated with ionic bonding. In exam answers, keep these two models separate because mixing up transfer and sharing is one of the quickest ways to lose definition marks.

Why do covalent bonds hold atoms together?

Covalent bonds hold atoms together because the shared pair of electrons is attracted to the positive nuclei of both bonded atoms. This electrostatic attraction holds the atoms in the molecule. For A-Level wording, it is better to mention both the shared pair and the attraction to nuclei.

Final Takeaway

For CAIE A-Level answers, do not stop at "shared electrons". Add the markscheme idea: electrostatic attraction between the shared pair and both nuclei.