AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    The electrons in an atom occupy the lowest available energy levels…

    Full specification wording

    Electronic structure: The electrons in an atom occupy the lowest available energy levels (innermost available shells). The electronic structure of an atom can be represented by numbers or by a diagram. For example, the electronic structure of sodium is 2,8,1 or

    Electrons in an atom fill the lowest available energy levels first, so the innermost shell fills before the next shell begins.

    Checked against the AQA 8464 specification (opens in a new tab) on .

    • Point 1 of 2
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Electrons in an atom fill the lowest available energy levels first, so the innermost shell fills before the next shell begins. The first shell holds up to 2 electrons, the second up to 8, and the third up to 8 for the first 20 elements. Electronic structure can be written as numbers, such as sodium 2,8,1, or drawn as a diagram with a nucleus and shells carrying dots or crosses. Sodium has 11 electrons: 2 in the first shell, 8 in the second and 1 in the third. The outer-shell electron explains sodium's position in Group 1 and its tendency to form a 1⁺ ion.

    What earns the marks

    • State that electrons occupy the lowest available energy levels, filling inner shells before outer shells.
    • Apply shell capacities: 2 in the first shell, 8 in the second and 8 in the third for the first 20 elements.
    • Represent electronic structure as numbers, such as 2,8,1 for sodium, or as a shell diagram.
    • Relate the number of outer-shell electrons to the element's group and its ion charge, for example sodium forming Na⁺.
    • Check that the total number of electrons equals the atomic number.

    Common mistakes and how to put them right

    • Filling the second shell with more than 8 electrons before starting the third.

      Put it right: The second shell holds a maximum of 8 for these elements.

    • Writing the electronic structure of sodium as 2,8,1 but drawing 11 electrons in the outer shell.

      Put it right: The diagram must match the numerical structure.

    • Confusing mass number with electron number.

      Put it right: In a neutral atom, electrons equal the atomic number, not the mass number.

    Exam tips

    • Count the electrons first from the atomic number, then allocate them shell by shell from the inside out.
    • When drawing a shell diagram, place the nucleus label centrally and use consistent symbols for electrons.
    • Use the outer-shell number to predict the group and ion charge, which links structure to periodic table patterns.

    Try the lesson

    The start of the Electronic structure: The electrons in an atom occupy the lowest available energy levels (innermost available shells). The electronic structure of an atom can be represented by numbers or by a diagram. For example, the electronic structure of sodium is 2,8,1 or lesson, made from checked teaching notes for this specification point.

    Have a go first

    An atom of lithium has three electrons. Which electronic structure shows how these electrons are arranged?

    Listen

    Electrons in an atom fill the lowest available energy levels first, so the innermost shell fills before the next shell begins. The first shell holds up to 2 electrons, the second up to 8, and the third up to 8 for the first 20 elements. Electronic structure can be written as numbers, such as sodium 2,8,1, or drawn as a diagram with a nucleus and shells carrying dots or crosses. Sodium has 11 electrons: 2 in the first shell, 8 in the second and 1 in the third. The outer-shell electron explains sodium's position in Group 1 and its tendency to form a 1⁺ ion. A strong answer earns marks for these points. State that electrons occupy the lowest available energy levels, filling inner shells before outer shells. Apply shell capacities: 2 in the first shell, 8 in the second and 8 in the third for the first 20 elements. Represent electronic structure as numbers, such as 2,8,1 for sodium, or as a shell diagram. Relate the number of outer-shell electrons to the element's group and its ion charge, for example sodium forming Na⁺. A common slip: Filling the second shell with more than 8 electrons before starting the third. Instead, the second shell holds a maximum of 8 for these elements. Exam tip: Count the electrons first from the atomic number, then allocate them shell by shell from the inside out.

    See it

    A top-down flowchart. The first box states that electrons occupy the lowest available energy levels. An arrow leads to a box saying the first shell fills first, then to a box saying the second shell fills next, then to a box saying the third shell fills next. From the third-shell box, two arrows branch out: one to a box saying the electronic structure is written as numbers, and one to a box saying it is drawn as a shell diagram. Both of these boxes lead to a box giving sodium as 2,8,1. From there an arrow leads to a final box saying the outer-shell electron relates to the group and ion charge.
    It shows electrons filling the lowest available energy levels from the innermost shell outwards, and how the resulting structure can be written as numbers or drawn as a diagram, using sodium 2,8,1 as the example.

    Key words

    Say what each word means before you turn the card.

    Energy levels and shells

    Try answering aloud or in your head before turning the card.

    Electron configuration notation

    Try answering aloud or in your head before turning the card.

    Shell diagrams

    Try answering aloud or in your head before turning the card.

    Links to group and ion formation

    Try answering aloud or in your head before turning the card.

    See every definition
    Energy levels and shells
    The regions electrons occupy, with the lowest available filled first so the innermost available shells fill before the next begins.
    Electron configuration notation
    A way of representing electronic structure as numbers, such as 2,8,1 for sodium.
    Shell diagrams
    A representation of electronic structure drawn as a diagram with a nucleus and shells carrying dots or crosses.
    Links to group and ion formation
    The outer-shell electron explains an element's position in a group and its tendency to form an ion.

    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. The first box states that electrons occupy the lowest available energy levels. An arrow leads to a box saying the first shell fills first, then to a box saying the second shell fills next, then to a box saying the third shell fills next. From the third-shell box, two arrows branch out: one to a box saying the electronic structure is written as numbers, and one to a box saying it is drawn as a shell diagram. Both of these boxes lead to a box giving sodium as 2,8,1. From there an arrow leads to a final box saying the outer-shell electron relates to the group and ion charge.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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