E.1 Structure of the atomIB Physics SL: Flashcards

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What did most alpha particles passing straight through gold foil show?

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What did most alpha particles passing straight through gold foil show?: The atom is mostly empty space.
What did the rare large-angle deflections show?: Positive charge and most of the mass are concentrated in a tiny, dense nucleus.
Why was the Geiger–Marsden experiment done in a vacuum?: Alpha particles would otherwise be absorbed or slowed by air within a few centimetres.
What do A and Z mean in $^{A}_{Z}\mathrm{X}$ ?: A = nucleon number (protons + neutrons); Z = proton number.
How do you find the number of neutrons?: N = A − Z.
What are isotopes?: Nuclides with the same proton number but different numbers of neutrons.
What is the photon energy when an electron changes level?: The difference between the two energy levels, ΔE = hf.
Convert 1 eV to joules.: 1 eV = 1.60 × 10⁻¹⁹ J.
What does an emission spectrum look like?: Bright coloured lines on a dark background.
What does an absorption spectrum look like?: A continuous spectrum crossed by dark lines.
Why do line spectra show that energy levels are discrete?: Only certain photon energies are emitted or absorbed, so only certain energy differences exist.
Why do absorption lines appear at the same wavelengths as emission lines?: The same pairs of energy levels are involved.
How are spectra used to find the composition of a star?: Dark line wavelengths are matched with the laboratory emission lines of each element.