AQA · GCSE · Combined Science

Course version: 8464 · Version from Sept 2018

Size and mass of atoms: The relative masses of protons, neutrons and electrons are:

Q: How do I revise Size and mass of atoms: The relative masses of protons, neutrons and electrons are: for GCSE?

Read the notes on Size and mass of atoms: The relative masses of protons, neutrons and electrons are:, then test yourself without looking. Answering questions and checking what you missed builds recall faster than re-reading.

Q: Is this Size and mass of atoms: The relative masses of protons, neutrons and electrons are: guide aligned to the AQA specification?

Yes. This guide is linked to the Size and mass of atoms: The relative masses of protons, neutrons and electrons are: topic in the AQA GCSE specification.

Relative mass compares the mass of a particle with a standard.

2 key terms

Study notes

From the checked teaching notes for this specification point.

The idea

What earns the marks

State that a proton has a relative mass of 1.
State that a neutron has a relative mass of 1.
State that an electron has a relative mass of about 1/1836, which is often treated as negligible.
Explain that these relative masses are comparisons, not actual masses in kilograms.
Use the values to calculate mass number as the sum of protons and neutrons, ignoring the electron contribution.

Common mistakes and how to put them right

Writing that an electron has a relative mass of 0.
Put it right by saying it is about 1/1836, which is very small but not zero.
Giving the relative mass of a neutron as 0.
Put it right by stating that a neutron has a relative mass of 1, like a proton.
Confusing relative mass with actual mass in kilograms.
Put it right by explaining that relative mass is a ratio compared with a standard, so it has no units.

Exam tips

Learn the values: proton 1, neutron 1, electron about 1/1836.
When calculating mass number, add protons and neutrons only; do not include electrons.
If asked to compare, state that protons and neutrons have similar relative masses, while electrons are much lighter.

Try the lesson

The start of the Size and mass of atoms: The relative masses of protons, neutrons and electrons are: lesson, made from checked teaching notes for this specification point.

Have a go first

In the table of relative masses, what is the relative mass of a proton?

Tip: press 1 to 4 to choose

Listen

Relative mass compares the mass of a particle with a standard. In GCSE Combined Science, a proton has a relative mass of 1, a neutron has a relative mass of 1, and an electron has a relative mass of about 1/1836, often treated as negligible. These values explain why the mass number of an atom is the sum of its protons and neutrons, and why electrons barely affect atomic mass. For example, a sodium atom with 11 protons and 12 neutrons has a mass number of 23; its 11 electrons add only about 0.006 to the relative mass. The values are relative, not actual masses in kilograms. A strong answer earns marks for these points. State that a proton has a relative mass of 1. State that a neutron has a relative mass of 1. State that an electron has a relative mass of about 1/1836, which is often treated as negligible. Explain that these relative masses are comparisons, not actual masses in kilograms. A common slip: Writing that an electron has a relative mass of 0. Instead, saying it is about 1/1836, which is very small but not zero. Exam tip: Learn the values: proton 1, neutron 1, electron about 1/1836.

See it

A top-down flowchart. Three nodes at the top give the relative masses: a proton has a relative mass of 1, a neutron has a relative mass of 1, and an electron has a relative mass of about 1/1836, often treated as negligible. The proton and neutron nodes both lead to a node stating that mass number equals protons plus neutrons. The electron node leads to a node stating that electrons barely affect atomic mass. Both of these then lead to a final node stating that the electron contribution is ignored in mass number. — It shows the relative masses of protons, neutrons and electrons and how they lead to mass number being the sum of protons and neutrons, with electrons ignored.

Key words

Say what each word means before you turn the card.

Relative mass

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Mass number

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See every definition

Relative mass: A comparison of the mass of a particle with a standard, so it is not an actual mass in kilograms.
Mass number: The sum of the protons and neutrons in an atom, ignoring the electron contribution.

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. Three nodes at the top give the relative masses: a proton has a relative mass of 1, a neutron has a relative mass of 1, and an electron has a relative mass of about 1/1836, often treated as negligible. The proton and neutron nodes both lead to a node stating that mass number equals protons plus neutrons. The electron node leads to a node stating that electrons barely affect atomic mass. Both of these then lead to a final node stating that the electron contribution is ignored in mass number.

1Box 1
2Box 2
3Box 3

0 of 3 labelled

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