Atomic Structure, Isotopes and Mass Spectrometry
Subatomic particles, isotopes, electronic configurations, successive ionisation energies and using mass spectra to determine isotopic abundance and relative mass.
How to study A-level Chemistry
Represent the species and process correctly, conserve atoms, charge and energy, calculate with units, then test the result against observations and chemical evidence.
Core concepts
Concept 1
Proton number defines an element; isotopes have the same proton number but different neutron numbers.
Exam cue: State whether the species is an atom or ion before writing its configuration.
Concept 2
Electrons occupy shells, subshells and orbitals according to energy, Pauli exclusion and electron repulsion.
Exam cue: Use large successive-ionisation-energy jumps to infer the number of outer electrons.
Concept 3
Mass spectra provide mass-to-charge and abundance evidence used to calculate relative isotopic or atomic mass.
Exam cue: Calculate a weighted mean from abundance, not a simple average of isotope masses.
Risk pitfalls and guardrails
Removing transition-metal electrons from the wrong subshell when forming ions.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Calling relative atomic mass the mass of one atom in grams.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Assuming every mass-spectrum peak is a different isotope.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Memory anchors
Isotope
Isotopes have the same number of protons but different numbers of neutrons.
Orbital
An orbital holds up to two electrons with opposite spins.
First Ionisation Energy
First ionisation energy removes one electron from each gaseous atom in one mole of atoms.
Mass-to-charge Ratio
A mass spectrometer separates ions according to m/z.
Relative Atomic Mass
Relative atomic mass is the abundance-weighted mean mass relative to one twelfth of carbon-12.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Which pair of nuclides has the same proton number but a different neutron number?
An atom contains 26 protons, 30 neutrons and 24 electrons. Which description is correct?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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