AQA · A-Level · Chemistry

    Course version: 7405 · Version from Sept 2016

    A single covalent bond contains a shared pair of electrons.

    Full specification wording

    Nature of covalent and dative covalent bonds: A single covalent bond contains a shared pair of electrons.

    A single covalent bond is one pair of electrons shared between two atoms.

    Checked against the AQA 7405 specification (opens in a new tab) on .

    • Point 1 of 4
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    A single covalent bond is one pair of electrons shared between two atoms. The bond exists because both positive nuclei are attracted to the same negative pair of electrons sitting between them, an electrostatic attraction that holds the atoms at a fixed separation where attraction and repulsion balance. In a dot-and-cross diagram, the shared pair sits in the overlap of the two circles, with one dot and one cross, and any electrons not involved are drawn as lone pairs. In a displayed formula, each shared pair is drawn as a single straight line. The bond is directional, which is why covalent substances form molecules with definite shapes or giant covalent lattices like diamond and silicon dioxide.

    What earns the marks

    • A shared pair of electrons between the two atoms.
    • Electrostatic attraction between the shared pair and both nuclei.
    • A dot-and-cross diagram showing one electron from each atom in the overlap.
    • Representing the shared pair as a single line in a displayed formula.

    Common mistakes and how to put them right

    • Describing covalent bonding as electrons being given or transferred.

    • Drawing a line to represent a single electron rather than a shared pair.

    • Saying the bond is an attraction between atoms without naming nuclei and the shared pair.

    • Assuming all covalent substances form simple molecules, forgetting giant covalent lattices.

    Exam tips

    • Say shared pair of electrons, not shared electrons; the pair is what earns the mark.
    • Include every outer electron in a dot-and-cross diagram, then check the total against the atoms present.
    • Use the word electrostatic when explaining what holds the atoms together.

    Try the lesson

    The start of the Nature of covalent and dative covalent bonds: A single covalent bond contains a shared pair of electrons. lesson, made from checked teaching notes for this specification point.

    Have a go first

    How many electrons are shared in a single covalent bond?

    Listen

    A single covalent bond is one pair of electrons shared between two atoms. The bond exists because both positive nuclei are attracted to the same negative pair of electrons sitting between them, an electrostatic attraction that holds the atoms at a fixed separation where attraction and repulsion balance. In a dot-and-cross diagram, the shared pair sits in the overlap of the two circles, with one dot and one cross, and any electrons not involved are drawn as lone pairs. In a displayed formula, each shared pair is drawn as a single straight line. The bond is directional, which is why covalent substances form molecules with definite shapes or giant covalent lattices like diamond and silicon dioxide. A strong answer earns marks for these points. a shared pair of electrons between the two atoms. electrostatic attraction between the shared pair and both nuclei. a dot-and-cross diagram showing one electron from each atom in the overlap. representing the shared pair as a single line in a displayed formula. Exam tip: Say shared pair of electrons, not shared electrons; the pair is what earns the mark.

    See it

    A top-down flowchart. At the top, a node labelled 'Two atoms' leads to 'Shared pair of electrons between them', which leads to 'Single covalent bond'. From 'Single covalent bond' four branches emerge. The first leads to 'Electrostatic attraction between the shared pair and both nuclei', which leads to 'Atoms held at a fixed separation where attraction and repulsion balance'. The second leads to 'Dot-and-cross diagram: shared pair in the overlap, one dot and one cross'. The third leads to 'Displayed formula: shared pair drawn as a single straight line'. The fourth leads to 'Bond is directional', which then branches to 'Molecules with definite shapes' and to 'Giant covalent lattices'.
    It shows how a shared pair of electrons between two atoms gives a single covalent bond, held by electrostatic attraction to both nuclei, and how that bond is represented and leads to definite shapes or giant covalent lattices.

    Key words

    Say what each word means before you turn the card.

    shared pair

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    electrostatic attraction to both nuclei

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    dot-and-cross diagrams

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    displayed formulae

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    See every definition
    shared pair
    One pair of electrons shared between two atoms, sitting between them in a single covalent bond.
    electrostatic attraction to both nuclei
    Both positive nuclei are attracted to the same negative pair of electrons sitting between them, holding the atoms at a fixed separation.
    dot-and-cross diagrams
    A diagram in which the shared pair sits in the overlap of the two circles, with one dot and one cross, and electrons not involved are drawn as lone pairs.
    displayed formulae
    A representation in which each shared pair is drawn as a single straight line.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. At the top, a node labelled 'Two atoms' leads to 'Shared pair of electrons between them', which leads to 'Single covalent bond'. From 'Single covalent bond' four branches emerge. The first leads to 'Electrostatic attraction between the shared pair and both nuclei', which leads to 'Atoms held at a fixed separation where attraction and repulsion balance'. The second leads to 'Dot-and-cross diagram: shared pair in the overlap, one dot and one cross'. The third leads to 'Displayed formula: shared pair drawn as a single straight line'. The fourth leads to 'Bond is directional', which then branches to 'Molecules with definite shapes' and to 'Giant covalent lattices'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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