AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
All atoms of a particular element have the same number of protons.
Full specification wording
Relative electrical charges of subatomic particles: All atoms of a particular element have the same number of protons.
Every atom of a given element has an identical proton count, and this fixed number is the atomic number.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 3 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Every atom of a given element has an identical proton count, and this fixed number is the atomic number. For example, all chlorine atoms contain 17 protons, whether they are chlorine-35 or chlorine-37; the isotopes differ only in neutron number. Because protons carry relative charge 1⁺, the nuclear charge is the same for all atoms of that element. The proton number does not change in chemical reactions; atoms gain, lose or share electrons instead. This constancy is why the periodic table can be arranged by increasing atomic number and why elements have consistent chemical identities. In the nuclear model, the nucleus contains these protons together with neutrons, while electrons occupy shells around it.
What earns the marks
- State that the proton number is fixed for all atoms of the same element.
- Identify the proton number as the atomic number of that element.
- Explain that isotopes of an element differ in neutrons, not protons.
- Recognise that chemical changes involve electrons, so proton number is unchanged.
- Use the constant proton number to justify an element's fixed position in the periodic table.
Common mistakes and how to put them right
Thinking isotopes have different proton numbers.
Put it right by stating that isotopes of an element have the same proton number but different neutron numbers.
Believing chemical reactions can change an element's proton number.
Put it right by explaining that reactions involve electron transfer or sharing, not nuclear change.
Assuming all atoms of an element have identical mass.
Put it right by noting that neutron number can vary between isotopes, changing mass number.
Exam tips
- Use the phrase same number of protons when defining an element, and add the atomic number value if one is given.
- For isotope questions, compare proton and neutron numbers in a simple table before writing your answer.
- If a reaction equation is shown, check that element symbols are unchanged to support your explanation.
Try the lesson
The start of the Relative electrical charges of subatomic particles: All atoms of a particular element have the same number of protons. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following statements is true for all atoms of a specific element?
Listen
Every atom of a given element has an identical proton count, and this fixed number is the atomic number. For example, all chlorine atoms contain 17 protons, whether they are chlorine-35 or chlorine-37; the isotopes differ only in neutron number. Because protons carry relative charge 1⁺, the nuclear charge is the same for all atoms of that element. The proton number does not change in chemical reactions; atoms gain, lose or share electrons instead. This constancy is why the periodic table can be arranged by increasing atomic number and why elements have consistent chemical identities. In the nuclear model, the nucleus contains these protons together with neutrons, while electrons occupy shells around it. A strong answer earns marks for these points. State that the proton number is fixed for all atoms of the same element. Identify the proton number as the atomic number of that element. Explain that isotopes of an element differ in neutrons, not protons. Recognise that chemical changes involve electrons, so proton number is unchanged. A common slip: Thinking isotopes have different proton numbers. Instead, stating that isotopes of an element have the same proton number but different neutron numbers. Exam tip: Use the phrase same number of protons when defining an element, and add the atomic number value if one is given.
See it
Key words
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Atomic number
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Isotopes
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Conservation of protons in chemical change
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See every definition
- Atomic number
- The fixed number of protons that every atom of a given element has.
- Isotopes
- Atoms of an element that differ only in neutron number, not in proton number.
- Conservation of protons in chemical change
- The proton number does not change in chemical reactions; atoms gain, lose or share electrons instead.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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