1.7.1Principles of Chemistry
Formation of Covalent Bonds
5 min read 4 parts Lesson 1 of 50 Unit quiz
Section 1 of 4Sharing Electrons
Covalent bonding lets atoms reach a stable outer shell without losing or gaining electrons completely.
Covalent bond
- The electrostatic attraction between a shared pair of electrons and the positive nuclei of the two atoms that share them.
Bonding pair
- A pair of electrons shared between two atoms, with normally one electron contributed by each atom.
Lone pair
- An outer-shell pair of electrons that is not involved in bonding, also called a non-bonding pair.
Stability
- Sharing gives each atom a full outer shell of eight electrons, or two for hydrogen, which makes the atoms more stable.
Section 2 of 4How a Bond Forms
1
Two chlorine atoms each have seven outer electrons, so each needs one more electron to fill its outer shell.
2
Each chlorine atom contributes one electron to a shared pair that sits between the two atoms.
3
The shared pair is attracted to both nuclei, which holds the two atoms together by a strong covalent bond.
4
Each chlorine atom now counts eight outer electrons, including the two in the shared pair, so both atoms are stable.
5
No ions form, because the electrons are shared rather than transferred from one atom to the other.
Section 3 of 4Covalent Compared with Ionic
Covalent Compared with Ionic
Bond strength
- Covalent bonds within molecules are strong and need a large amount of energy to break.
Examples
- Hydrogen, oxygen, water and diamond all contain covalent bonds joining their atoms together.
Between molecules
- The forces between separate molecules are much weaker than the covalent bonds inside them.
| Feature | Covalent bonding | Ionic bonding |
|---|---|---|
| Electrons | Shared | Transferred |
| Particles formed | Molecules or giant structures | Ions |
| Typical elements | Non-metal with non-metal | Metal with non-metal |
| Charge on particles | Neutral | Charged ions |
Section 4 of 4Exam Checklist & Tips
1.7.1 – Key Points for the Exam
- Covalent bond A shared pair of electrons holding two atoms together.
- Bonding pair Two electrons shared between two atoms in a covalent bond.
- Lone pair A pair of outer electrons on one atom that is not shared.
- Non-metal An element that usually forms covalent bonds by sharing electrons.
- Noble gas configuration The stable outer-shell arrangement of a noble gas, with eight electrons in most cases.
Common Mistakes
- Describing a covalent bond as a transfer of electrons, which describes ionic bonding.
- Forgetting that the covalent bond is an attraction between the shared electrons and the two nuclei.
- Describing shared electrons as fixed in one place; they are better regarded as a charge cloud that moves.
- Saying a covalent bond breaks when a simple molecular substance melts;
- melting overcomes the weak forces between molecules.