A sample of boron contains 19.9% boron-10 and 80.1% boron-11. Calculate the relative atomic mass of boron to 1 decimal place.
[2 marks]
Total for this question: 2
Chemistry
Atomic structure
AQA 3.1.1
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
Board and spec code confirmed against AQA 7405 · registry checked 2026-07-11How this checking works
The topic on one screen
- Protons and neutrons in the nucleus, electrons in shells. Mass number = protons + neutrons; isotopes differ only in neutron number.
- Relative atomic mass = the mean mass of an atom divided by 1/12 the mass of a carbon-12 atom.
- TOF mass spectrometer: ionise → accelerate → ion drift (separate by m/z) → detect. Ions must be charged to be accelerated and to make a current.
- At the detector, each positive ion gains an electron; the current produced is proportional to that ion's abundance.
- Ar from a spectrum: (sum of isotope mass x abundance) / (total abundance).
- Ionisation energy rises across a period (more nuclear charge, similar shielding) and falls down a group (outer electron further out and more shielded).
Where students actually lose marks
In the Ar definition, 'mean mass' and comparison to 1/12 the mass of a carbon-12 atom were crucially missed. Give the full definition, not just 'average mass of the atoms'.
June 2024 Paper 1 examiner report (Q01.2)
In mass spectra, students knew a current is produced but not why: the ion gains an electron at the detector, and the current is proportional to abundance. State both.
June 2023 Paper 1 examiner report (Q09.3)
In the relative-mass calculation, common errors were giving the mass of one atom rather than one mole, and not giving the mass number as an integer.
June 2024 Paper 1 examiner report (Q01.4)
Try it — exam-style
Medium
ORIGINAL · after June 2023 Paper 1 Q09.4
Easy
ORIGINAL · after June 2024 Paper 1 Q01.2
Define relative atomic mass.
[2 marks]
Total for this question: 2
Medium
ORIGINAL · after June 2023 Paper 1 Q09.3
In a TOF mass spectrometer, explain how the ions produce a signal at the detector and what the size of the signal tells you.
[2 marks]
Total for this question: 2
Medium
ORIGINAL
Explain why the first ionisation energy of magnesium is higher than that of sodium.
[2 marks]
Total for this question: 2
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