E.1 Structure of the atomIB Physics HL: Flashcards

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What did the Geiger–Marsden experiment show?

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What did the Geiger–Marsden experiment show?: Atoms are mostly empty space with a tiny, dense, positive nucleus.
How many neutrons in $^{A}_{Z}\mathrm{X}$ ?: N = A − Z.
What is the energy of a photon emitted in an atomic transition?: The difference between the energy levels: hf = ΔE.
How do spectra show discrete energy levels?: Only certain wavelengths are emitted or absorbed, so only certain energy differences exist.
How do spectra reveal a star's composition?: Dark absorption lines are matched to the laboratory emission lines of elements.
HL: Nuclear radius formula?: R = R₀A^(1/3), with R₀ ≈ 1.20 × 10⁻¹⁵ m.
HL: Why is nuclear density the same for all nuclei?: Mass ∝ A and volume ∝ R³ ∝ A, so A cancels.
HL: Approximate nuclear density?: About 2.3 × 10¹⁷ kg m⁻³.
HL: How is the distance of closest approach found?: Set the alpha particle's kinetic energy equal to kq₁q₂/d and solve for d.
HL: Why does Rutherford scattering fail at high energies?: The alpha particle gets close enough to feel the strong nuclear force, not just electrostatic repulsion.
HL: Bohr's quantisation condition?: mvr = nh/2π.
HL: Energy levels of hydrogen in the Bohr model?: E = −13.6/n² eV.
HL: Main limitation of the Bohr model?: It only works for one-electron atoms such as hydrogen; it fails for helium and heavier atoms.