Wzorowane na: Chemistry HL Paper 2, May 2025, TZ2, pytanie 2(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Informacja do zadań 2a-2c.
Gallium, a group 13 metal, melts at about 30 °C and is used in semiconductors such as gallium arsenide.
Gallium was discovered in 1875 from its atomic emission spectrum, which contains two strong violet lines.
(i) State which feature of an emission spectrum allows the ionization energy of the element to be determined.
(ii) Using sections 1, 2 and 9 of the data booklet, calculate the wavelength of the radiation whose photons have energy equal to the first ionization energy of a gallium atom.
(iii) The first ionization energy of germanium is higher than that of gallium. Explain this difference in terms of nuclear charge and the shielding of the outer electrons.
(i) the convergence limit «of the lines at the high-frequency end of the spectrum» ✔
(ii) energy per atom «» «J» ✔
frequency «
wavelength «
(iii) germanium has the greater nuclear charge «32 protons compared with 31» ✔
the shielding is the same in both atoms, because the valence electrons are in the same energy level / the number of inner electrons is the same, so the valence electron of gallium is held less strongly ✔
(i) [1] convergence limit; accept 'high-energy limit of the continuum'. (ii) [3] M1 energy per atom; M2 frequency; M3 wavelength; award [3] for a correct final answer; ECF at each step. (iii) [2] M1 nuclear charge comparison; M2 shielding unchanged. Do not accept 'germanium atoms are smaller' for M1.
In (ii) the ionization energy in section 9 is per mole; dividing by the Avogadro constant before using E = hf is the step most often omitted.
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