Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

1.7.1Principles of Chemistry

Formation of Covalent Bonds — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions

5 min read 11 parts Lesson 41 of 50

📚 Edexcel International GCSE Science Double Award 4SD0 - Chemistry Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read

Part 1 of 5Why atoms share electrons

Non-metals bonding together
  • Non-metals bonding together When two non-metal atoms react, neither can easily lose electrons, so they share them instead.
Shared pairs
  • Shared pairs A covalent bond is a shared pair of electrons between two atoms.
    • Each atom contributes one electron to the pair.
Full outer shells
  • Full outer shells By sharing, each atom has access to enough electrons to fill its outer shell, which makes the molecule stable.

Part 2 of 5How a covalent bond holds atoms together

1Atoms approach
  • Atoms approach The outer shells of two atoms overlap.
2Electrons shared
  • Electrons shared A pair of electrons is held in the region between the two nuclei.
3Electrostatic attraction
  • Electrostatic attraction Both positive nuclei are attracted to the shared negative electrons, and this strong attraction is the bond.
4Molecule formed
  • Molecule formed The atoms stay joined as a molecule with a definite formula.

Part 3 of 5Single, double and triple bonds

Bond typeShared pairsExampleDrawn as
Single1H2, Cl2, HCl, H2O, CH4H–H
Double2O2, CO2, C2H4O=O
Triple3N2N≡N

Part 4 of 5Common simple molecules

Covalent molecules
Hydrogen, H2
  • Hydrogen, H2 Each hydrogen atom has one electron and needs one more to have two, a full first shell, so they share one pair.
Chlorine, Cl2
  • Chlorine, Cl2 Each atom has seven outer electrons and needs one more, so one pair is shared.
Water, H2O
  • Water, H2O Oxygen shares one pair with each of two hydrogen atoms, leaving two non-bonding pairs on oxygen.
Methane, CH4
  • Methane, CH4 Carbon has four outer electrons and shares each with a hydrogen atom, making four single bonds.
Oxygen, O2 and nitrogen, N2
  • Oxygen, O2 and nitrogen, N2 Oxygen atoms need two more electrons, so they share two pairs.
    • Nitrogen atoms need three more, so they share three pairs.

Part 5 of 5Covalent compared with ionic bonding

Which elements
  • Which elements Covalent bonding happens between non-metal atoms;
    • ionic bonding is between a metal and a non-metal.
What happens to electrons
  • What happens to electrons In covalent bonds electrons are shared; in ionic bonds they are transferred.
Strength
  • Strength The covalent bond within a molecule is strong, but this tells us nothing about the forces between molecules, which are weak.

Key terms

TermMeaning
Covalent bondA shared pair of electrons that holds two atoms together.
MoleculeA group of atoms joined by covalent bonds.
Single bondA covalent bond with one shared pair of electrons.
Double bondA covalent bond with two shared pairs of electrons.
Triple bondA covalent bond with three shared pairs of electrons.

Avoid these mistakes

1
Saying that electrons are transferred in covalent bonding. They are shared.
2
Counting a double bond as two electrons in total; it is two shared pairs, so four electrons.
3
Thinking the covalent bond is the attraction between molecules. It is the attraction between nuclei and shared electrons within a molecule.
4
Forgetting that hydrogen needs only two electrons in its outer shell.

Last updated:

\n