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Atomic structure
This topic links the structure of atoms and ions to mass spectrometry, isotope abundance, electron configuration and periodic trends.
15
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaA LevelChemistryPhysical chemistry
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Syllabus checklist
What you need to know
15 objective pages available
Fundamental particles4 objectives
- Explain that scientific understanding of atomic structure has developed over time.
- State the relative charge and relative mass of protons, neutrons and electrons.
- Describe an atom as a nucleus containing protons and neutrons surrounded by electrons.
- Use particle properties to compare atoms, ions and isotopes.
Mass number, isotopes and mass spectrometry6 objectives
- Determine the numbers of protons, neutrons and electrons in atoms and ions from mass number, atomic number and charge.
- Explain the existence of isotopes using different neutron numbers.
- Describe the principles of a simple time-of-flight mass spectrometer: ionisation, acceleration, ion drift, detection and data analysis.
- Interpret simple mass spectra of elements.
- Calculate relative atomic mass from isotopic abundance data for mononuclear ions.
- Report isotope and mass-spectrometry calculations to an appropriate number of significant figures.
Electron configuration and ionisation energy5 objectives
- Write electron configurations of atoms and ions up to atomic number 36 using shells and s, p and d subshells.
- Define first ionisation energy.
- Write equations for first and successive ionisation energies.
- Explain how first and successive ionisation energies provide evidence for shells and subshells.
- Interpret ionisation energy data for Period 3 and Group 2 elements.
Key terms
Plum‑pudding modelGold‑foil experimentProtonNeutronNucleusAtomic numberIsotopeIonMass numberTime‑of‑flight (TOF)Mass‑to‑charge ratio (m/z)Relative Atomic Mass
Exam tips
- Structure of historical answer: Always state the observation, the conclusion, and the significance when describing experiments like Thomson’s or Rutherford’s.
- Use the symbol ‘e’ for elementary charge: When writing charges, use +1e, –1e, or 0e to avoid ambiguity.
Common mistakes
- Misinterpreting α‑particle scattering: Explain that the small fraction of deflected particles shows the nucleus is tiny but highly charged, not that it occupies most of the atom’s volume.
- Confusing the charge of a proton and an electron: Remember the proton is +1e, the electron is –1e, and the neutron is neutral.
Practice preview
- Which model best describes J.J. Thomson’s view of the atom?
- Explain how Rutherford’s gold‑foil experiment led to the nuclear model of the atom.
- Calculate the radius of the first Bohr orbit of a hydrogen atom. Use the formula a₀ = (4πϵ₀ħ²)/(mₑe²). Given ϵ₀ = 8.854×10⁻¹² C²·N⁻¹·m⁻², ħ = 1.055×10⁻³⁴ J·s, mₑ = 9.109×10⁻³¹ kg, e = 1.602×10⁻¹⁹ C.
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