The method and the results are on the photoelectron spectroscopy lab. Do the analysis yourself first, then check the answers below.
Quick answer: Electrons fill subshells in order of energy, giving each atom a configuration. These answers go with the AP Chemistry lab on photoelectron spectroscopy: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Model answers use the sample table. Wavelengths seen by eye are approximate, so small differences from your readings are expected.
Li 1240/671 = 1.85 eV; Na 1240/589 = 2.11 eV; K 1240/766 = 1.62 eV; Ca 1240/622 = 1.99 eV; Ba 1240/524 = 2.37 eV. Energies: 1.85, 2.11, 1.62, 1.99, 2.37 eV.
Question 2 Photon energy in joules
E = (6.626 × 10⁻³⁴ × 2.998 × 10⁸)/(589 × 10⁻⁹) = 3.37 × 10⁻¹⁹ J, which equals 2.11 eV.
Question 3 Order of energies
K (1.62), Li (1.85), Ca (1.99), Na (2.11), Ba (2.37 eV) from lowest to highest.
Question 4 Origin of the light
The flame promotes an electron to a higher energy level. When it falls back, the energy difference ΔE leaves as a photon of wavelength λ = hc/ΔE. Only certain ΔE exist, so only certain wavelengths are emitted.
Question 5 Trend in group 1
The valence electron is in a different shell in each atom, and the spacings between the energy levels differ because Zeff, shielding and distance differ. So the photon energies differ.
Question 6 Reliability
Sodium’s strong yellow light can hide weaker colours. Use fresh, clean splints and a new rinse for each test so that residue from the previous solution is not carried over.
Question 7 Improvement
Record the flame spectrum with a digital spectrometer or a camera with a diffraction grating, and read the peak positions on a calibrated scale. A calibrated instrument removes the observer’s colour judgement.
