AQA · A-Level · Chemistry

    Course version: 7405 · Version from Sept 2016

    An atom consists of a nucleus containing protons and neutrons surrounded…

    Full specification wording

    Fundamental particles: An atom consists of a nucleus containing protons and neutrons surrounded by electrons.

    An atom is mostly empty space.

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

    • Point 3 of 3
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    An atom is mostly empty space. The nucleus holds the protons and neutrons and is around 10⁻¹⁵ m across, while the whole atom is about 10⁻¹⁰ m, so the nucleus is roughly one hundred-thousandth of the diameter yet carries almost all the mass. The electrons occupy shells around it, held by electrostatic attraction between their negative charge and the positive nucleus. Because the proton and electron charges are equal and opposite, a neutral atom contains equal numbers of each; gaining or losing electrons, never protons, is what produces ions. Chemical behaviour is decided by the outer electrons, which is why isotopes of one element react identically while the nucleus differs.

    What earns the marks

    • Protons and neutrons located in the nucleus.
    • Electrons arranged in shells or energy levels around the nucleus.
    • Stating that the nucleus is very small compared with the atom but contains almost all the mass.
    • Equal numbers of protons and electrons making the atom neutral overall.

    Common mistakes and how to put them right

    • Placing electrons inside the nucleus or neutrons in the shells.

    • Saying an atom becomes an ion by gaining or losing protons.

    • Claiming the nucleus takes up most of the volume because it holds most of the mass.

    • Describing the electrons as held by gravity rather than electrostatic attraction.

    Exam tips

    • Quote the two order-of-magnitude sizes when asked to compare the nucleus with the atom; a comparison scores better than an adjective.
    • Say electrostatic attraction, not just attraction, whenever you explain what holds electrons to the nucleus.
    • Check any ion answer by confirming that only the electron count has changed.

    Try the lesson

    The start of the Fundamental particles: An atom consists of a nucleus containing protons and neutrons surrounded by electrons. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which subatomic particle is found in the nucleus of an atom and carries a positive charge?

    Listen

    An atom is mostly empty space. The nucleus holds the protons and neutrons and is around 10⁻¹⁵ m across, while the whole atom is about 10⁻¹⁰ m, so the nucleus is roughly one hundred-thousandth of the diameter yet carries almost all the mass. The electrons occupy shells around it, held by electrostatic attraction between their negative charge and the positive nucleus. Because the proton and electron charges are equal and opposite, a neutral atom contains equal numbers of each; gaining or losing electrons, never protons, is what produces ions. Chemical behaviour is decided by the outer electrons, which is why isotopes of one element react identically while the nucleus differs. A strong answer earns marks for these points. protons and neutrons located in the nucleus. electrons arranged in shells or energy levels around the nucleus. stating that the nucleus is very small compared with the atom but contains almost all the mass. equal numbers of protons and electrons making the atom neutral overall. Exam tip: Quote the two order-of-magnitude sizes when asked to compare the nucleus with the atom; a comparison scores better than an adjective.

    See it

    A top-down flowchart starting from a node labelled Atom. From Atom, arrows lead to Nucleus, to Electrons in shells, and to a node stating that a neutral atom has equal numbers of protons and electrons. From Nucleus, arrows lead to Protons, to Neutrons, and to a node giving the nucleus as about 10⁻¹⁵ m across. From Atom, another arrow leads to a node giving the whole atom as about 10⁻¹⁰ m. From Electrons in shells, an arrow leads to a node saying they are held by electrostatic attraction to the positive nucleus. From the neutral atom node, an arrow leads to a node saying ions form by gaining or losing electrons, never protons.
    It shows that an atom consists of a nucleus containing protons and neutrons, surrounded by electrons in shells, with the nucleus much smaller than the whole atom and the atom neutral when protons and electrons are equal.

    Key words

    Say what each word means before you turn the card.

    nuclear model

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

    shells and energy levels

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

    electrostatic attraction

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

    electrical neutrality

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

    See every definition
    nuclear model
    An atom consists of a nucleus containing protons and neutrons surrounded by electrons.
    shells and energy levels
    The electrons occupy shells around the nucleus, held by electrostatic attraction between their negative charge and the positive nucleus.
    electrostatic attraction
    The force between the negative charge of the electrons and the positive nucleus that holds the electrons to the nucleus.
    electrical neutrality
    Because the proton and electron charges are equal and opposite, a neutral atom contains equal numbers of each.

    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 starting from a node labelled Atom. From Atom, arrows lead to Nucleus, to Electrons in shells, and to a node stating that a neutral atom has equal numbers of protons and electrons. From Nucleus, arrows lead to Protons, to Neutrons, and to a node giving the nucleus as about 10⁻¹⁵ m across. From Atom, another arrow leads to a node giving the whole atom as about 10⁻¹⁰ m. From Electrons in shells, an arrow leads to a node saying they are held by electrostatic attraction to the positive nucleus. From the neutral atom node, an arrow leads to a node saying ions form by gaining or losing electrons, never protons.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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