AQA · GCSE · Chemistry

    Course version: 8462 · Version from Sept 2018

    The number of atoms, molecules or ions in a mole of a given substance is…

    Full specification wording

    Moles (HT only): The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant. The value of the Avogadro constant is 6.02 x 10 per mole.

    The Avogadro constant is the number of particles in one mole of any substance.

    Checked against the AQA 8462 specification (opens in a new tab) on .

    • Point 4 of 6
    • 3 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    The Avogadro constant is the number of particles in one mole of any substance. Its value is 6.02 × 10²³ per mole. This means that one mole of carbon contains 6.02 × 10²³ carbon atoms, one mole of water contains 6.02 × 10²³ water molecules, and one mole of sodium chloride contains 6.02 × 10²³ formula units of NaCl. The constant links the microscopic world of particles to the macroscopic world of masses we can measure. To find the number of particles in a given amount in moles, multiply the number of moles by 6.02 × 10²³. To find the amount in moles from a number of particles, divide by 6.02 × 10²³. The type of particle must always be stated.

    What earns the marks

    • State that the Avogadro constant is the number of particles in one mole of a substance.
    • Recall the value 6.02 × 10²³ per mole and use it in calculations.
    • Calculate the number of particles by multiplying the amount in moles by 6.02 × 10²³.
    • Calculate the amount in moles by dividing the number of particles by 6.02 × 10²³.

    Common mistakes and how to put them right

    • Writing the Avogadro constant without the correct power of ten, such as 6.02 × 10²².

      Put it right by using 6.02 × 10²³.

    • Forgetting to state the particle type when giving the number of particles.

      Put it right by naming atoms, molecules, ions or formula units.

    • Multiplying by the Avogadro constant when converting from particles to moles.

      Put it right by dividing the number of particles by 6.02 × 10²³.

    Exam tips

    • Write the Avogadro constant in standard form with the correct exponent.
    • Show the calculation clearly, including whether you are multiplying or dividing by 6.02 × 10²³.
    • Give the particle type in your final answer, for example 'molecules of CO₂'.

    Try the lesson

    The start of the Moles (HT only): The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant. The value of the Avogadro constant is 6.02 x 10 per mole. lesson, made from checked teaching notes for this specification point.

    Have a go first

    What is the value of the Avogadro constant, which gives the number of particles in one mole of a substance?

    Listen

    The Avogadro constant is the number of particles in one mole of any substance. Its value is 6.02 × 10²³ per mole. This means that one mole of carbon contains 6.02 × 10²³ carbon atoms, one mole of water contains 6.02 × 10²³ water molecules, and one mole of sodium chloride contains 6.02 × 10²³ formula units of NaCl. The constant links the microscopic world of particles to the macroscopic world of masses we can measure. To find the number of particles in a given amount in moles, multiply the number of moles by 6.02 × 10²³. To find the amount in moles from a number of particles, divide by 6.02 × 10²³. The type of particle must always be stated. A strong answer earns marks for these points. State that the Avogadro constant is the number of particles in one mole of a substance. Recall the value 6.02 × 10²³ per mole and use it in calculations. Calculate the number of particles by multiplying the amount in moles by 6.02 × 10²³. Calculate the amount in moles by dividing the number of particles by 6.02 × 10²³. A common slip: Writing the Avogadro constant without the correct power of ten, such as 6.02 × 10²². Instead, using 6.02 × 10²³. Exam tip: Write the Avogadro constant in standard form with the correct exponent.

    See it

    A top-down flowchart. The first box reads 'One mole of a substance' and points down to a box reading 'Contains 6.02 × 10²³ particles', which points down to a box reading 'State the particle type: atoms, molecules, ions or formula units'. Separately, a box reading 'Amount in moles' points down to 'Multiply by 6.02 × 10²³', which points down to 'Number of particles'. That box points down to 'Divide by 6.02 × 10²³', which points back to 'Amount in moles', forming a loop between moles and number of particles.
    Shows that one mole contains 6.02 × 10²³ particles, that the particle type must be stated, and how multiplying or dividing by the Avogadro constant converts between moles and number of particles.

    Key words

    Say what each word means before you turn the card.

    Avogadro constant

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    Mole calculations

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    Amounts of substance

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    See every definition
    Avogadro constant
    The number of atoms, molecules or ions in a mole of a given substance, with a value of 6.02 × 10²³ per mole.
    Mole calculations
    Multiplying the amount in moles by 6.02 × 10²³ gives the number of particles, and dividing the number of particles by 6.02 × 10²³ gives the amount in moles.
    Amounts of substance
    The amount in moles, from which the number of particles is found by multiplying by 6.02 × 10²³.

    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 reads 'One mole of a substance' and points down to a box reading 'Contains 6.02 × 10²³ particles', which points down to a box reading 'State the particle type: atoms, molecules, ions or formula units'. Separately, a box reading 'Amount in moles' points down to 'Multiply by 6.02 × 10²³', which points down to 'Number of particles'. That box points down to 'Divide by 6.02 × 10²³', which points back to 'Amount in moles', forming a loop between moles and number of particles.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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