AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Atoms can be represented as shown in this example: Atoms of the same…
Full specification wording
Mass number, atomic number and isotopes: Atoms can be represented as shown in this example: Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.
A nuclide symbol carries three pieces of information: the chemical symbol, the mass number above it and the atomic number below it, as in ¹⁴₆C. Isotopes are atoms of the same element, so they…
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 5 of 7
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A nuclide symbol carries three pieces of information: the chemical symbol, the mass number above it and the atomic number below it, as in ¹⁴₆C. Isotopes are atoms of the same element, so they share the atomic number, but they hold different numbers of neutrons and therefore have different mass numbers. Carbon-12 and carbon-14 both have six protons; one has six neutrons and the other eight. Since the electron arrangement is unchanged, isotopes of an element behave identically in chemical reactions but differ in mass and in nuclear stability, which is why carbon-14 is radioactive while carbon-12 is not. Examiners ignore any mention of electron numbers in the definition.
What earns the marks
- Isotopes being atoms of the same element, with the same number of protons.
- Stating that they have different numbers of neutrons.
- The equivalent wording, the same atomic number but a different mass number.
- Reading the nuclide symbol correctly, mass number above and atomic number below.
Common mistakes and how to put them right
Defining isotopes by a difference in the number of electrons, which the mark scheme ignores.
Claiming isotopes of an element are different elements.
Saying the atomic number differs between isotopes.
Writing the mass number in the lower position of the nuclide symbol.
Exam tips
- A two-mark definition needs both halves: same protons and different neutrons.
- Naming an isotope as carbon-14 tells you the mass number, so the neutron count is 14 minus the atomic number.
- Do not mention electrons in an isotopes definition; it wins nothing and can cost clarity.
Try the lesson
The start of the Mass number, atomic number and isotopes: Atoms can be represented as shown in this example: Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element. lesson, made from checked teaching notes for this specification point.
Have a go first
Two atoms of the same element have different numbers of neutrons. What name is given to atoms of this type?
Listen
A nuclide symbol carries three pieces of information: the chemical symbol, the mass number above it and the atomic number below it, as in ¹⁴₆C. Isotopes are atoms of the same element, so they share the atomic number, but they hold different numbers of neutrons and therefore have different mass numbers. Carbon-12 and carbon-14 both have six protons; one has six neutrons and the other eight. Since the electron arrangement is unchanged, isotopes of an element behave identically in chemical reactions but differ in mass and in nuclear stability, which is why carbon-14 is radioactive while carbon-12 is not. Examiners ignore any mention of electron numbers in the definition. A strong answer earns marks for these points. isotopes being atoms of the same element, with the same number of protons. stating that they have different numbers of neutrons. the equivalent wording, the same atomic number but a different mass number. reading the nuclide symbol correctly, mass number above and atomic number below. Exam tip: A two-mark definition needs both halves: same protons and different neutrons.
See it
Key words
Say what each word means before you turn the card.
isotopes
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nuclide notation
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mass number
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See every definition
- isotopes
- Atoms of the same element that have different numbers of neutrons.
- nuclide notation
- A representation carrying the chemical symbol, the mass number above it and the atomic number below it.
- mass number
- The number written above the chemical symbol in a nuclide symbol, which differs between isotopes of an element.
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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