AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Key ideas: electron sharing
Electron sharing is the process by which non-metal atoms form covalent bonds.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 19 of 26
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Electron sharing is the process by which non-metal atoms form covalent bonds. Each atom contributes at least one electron to a shared pair, and the shared pair is attracted to the nuclei of both atoms, holding them together. For example, in a hydrogen molecule, H₂, two hydrogen atoms each contribute one electron to a shared pair, giving each atom a full outer shell like helium. In water, H₂O, the oxygen atom shares one pair with each of two hydrogen atoms, so oxygen has two shared pairs plus two lone pairs. Dot-and-cross diagrams show the outer-shell electrons only, using dots for one atom and crosses for the other, so shared pairs appear in the overlap region.
What earns the marks
- A covalent bond forms when a pair of electrons is shared between two non-metal atoms.
- Each atom in the shared pair contributes at least one electron to the bond.
- The shared pair is attracted to the nuclei of both bonded atoms, which holds the atoms together.
- Dot-and-cross diagrams show outer-shell electrons only, with shared pairs in the overlap between the atoms.
- Simple molecules such as H₂, Cl₂, HCl, H₂O, NH₃, CH₄, O₂, N₂ and CO₂ can be represented using dot-and-cross diagrams.
- Atoms in a covalent bond achieve the electronic structure of a noble gas, often a full outer shell.
Common mistakes and how to put them right
Drawing all electrons as dots instead of using dots for one atom and crosses for the other.
Put it right: Use one symbol for each atom so the origin of every shared electron is clear.
Showing inner-shell electrons in a dot-and-cross diagram.
Put it right: Show outer-shell electrons only, because these are the electrons involved in bonding.
Describing covalent bonding as the transfer of electrons.
Put it right: Transfer describes ionic bonding, whereas covalent bonding involves sharing a pair of electrons.
Exam tips
- Count the outer-shell electrons for each atom before drawing, then pair them up so every atom reaches a full outer shell where possible.
- Label shared pairs clearly and check that each bond contains exactly two electrons, one from each atom.
- When explaining a diagram, state that the shared pair is attracted to both nuclei, rather than saying the atoms 'want' electrons.
Try the lesson
The start of the Key ideas: electron sharing lesson, made from checked teaching notes for this specification point.
Have a go first
In which type of bonding do atoms share pairs of electrons?
Listen
Electron sharing is the process by which non-metal atoms form covalent bonds. Each atom contributes at least one electron to a shared pair, and the shared pair is attracted to the nuclei of both atoms, holding them together. For example, in a hydrogen molecule, H₂, two hydrogen atoms each contribute one electron to a shared pair, giving each atom a full outer shell like helium. In water, H₂O, the oxygen atom shares one pair with each of two hydrogen atoms, so oxygen has two shared pairs plus two lone pairs. Dot-and-cross diagrams show the outer-shell electrons only, using dots for one atom and crosses for the other, so shared pairs appear in the overlap region. A strong answer earns marks for these points. A covalent bond forms when a pair of electrons is shared between two non-metal atoms. Each atom in the shared pair contributes at least one electron to the bond. The shared pair is attracted to the nuclei of both bonded atoms, which holds the atoms together. Dot-and-cross diagrams show outer-shell electrons only, with shared pairs in the overlap between the atoms. A common slip: Drawing all electrons as dots instead of using dots for one atom and crosses for the other. Instead, use one symbol for each atom so the origin of every shared electron is clear. Exam tip: Count the outer-shell electrons for each atom before drawing, then pair them up so every atom reaches a full outer shell where possible.
See it
Key words
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Covalent bonding
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Shared electron pairs
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Dot-and-cross diagrams
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See every definition
- Covalent bonding
- A bond that forms when a pair of electrons is shared between two non-metal atoms, with the shared pair attracted to the nuclei of both atoms.
- Shared electron pairs
- A pair of electrons in which each atom contributes at least one electron, and the pair is attracted to the nuclei of both bonded atoms.
- Dot-and-cross diagrams
- Diagrams that show outer-shell electrons only, using dots for one atom and crosses for the other, so shared pairs appear in the overlap region.
Label the diagram
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1Box 1
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3Box 3
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