Quick answer: Electrons fill subshells in order of energy, giving each atom a configuration. This AP Chemistry worksheet on photoelectron spectroscopy gives 20 problems from easy to hard: configuration of sulfur, configuration of a cation and chromium and copper. The worked answers are on a separate page, and the worksheet is a free printable PDF.
These 20 problems cover electron configurations, ions of transition metals, photoelectron spectra, successive ionisation energies and periodic trends explained with Coulomb’s law.
They follow AP Chemistry unit 1. Early problems ask for configurations and short answers. Later ones need quantitative reasoning and paragraph arguments in the style of free-response questions.
Level: AP Chemistry · Curriculum: AP Chem Unit 1
Problem 1 Configuration of sulfur ★★★
Sulfur has atomic number 16.1. Write its full electron configuration.
2. Then state the number of valence electrons.
3. Finally, write the noble-gas short form.
Problem 2 Configuration of a cation ★★★
Calcium has atomic number 20.1. Write the configuration of a calcium atom.
2. Then write the configuration of Ca²⁺.
3. Finally, name the noble gas with the same configuration.
Problem 3 Chromium and copper ★★★
Wanjiru in Nairobi writes copper as [Ar] 4s² 3d⁹.1. Give the correct configuration.
2. Then explain why the correct configuration is more stable.
Problem 4 Unpaired electrons in nitrogen ★★★
Nitrogen has atomic number 7.1. Draw the 2p orbital box diagram for nitrogen, using arrows.
2. Then state the number of unpaired electrons.
3. Finally, name the rule that decides this arrangement.
Problem 5 Identify the element from PES ★★★
The figure shows a photoelectron spectrum of an element.1. Give the subshell for each peak.
2. Then write the configuration and name the element.
3. Finally, state which peak corresponds to the valence electron.
Problem 6 Coulomb’s law quick checks ★★★
Two charged particles attract each other with force F.1. State the new force when the distance doubles.
2. Then state the new force when one charge doubles.
3. Finally, state the new force when one charge doubles and the distance halves.
Problem 7 Which atom is bigger? ★★★
Compare sodium and chlorine atoms, both in period 3.1. State which has the larger radius.
2. Then explain using effective nuclear charge.
Problem 8 Effective nuclear charge ★★★
Estimate Zeff ≈ Z − core electrons for the valence electrons of Mg (Z = 12), Si (Z = 14) and Cl (Z = 17), all with 10 core electrons.1. Calculate the three values.
2. Then predict which element has the smallest radius.
3. Finally, predict which has the greatest first ionisation energy.
Problem 9 Successive ionisation energies ★★★
An element has ionisation energies of 578, 1817, 2745, 11577 and 14842 kJ/mol.1. Identify the electron number after which the large jump occurs.
2. Then state the number of valence electrons.
3. Finally, identify the element in period 3.
Problem 10 Comparing two spectra ★★★
Look at the two spectra in the figure. They have the same peak heights, 2 : 2 : 6 : 2 : 1 (A) and 2 : 2 : 6 : 2 : 3 (B).1. Identify elements A and B.
2. Then explain why the 1s peak of B is at higher binding energy than A.
3. Finally, state the difference in the valence peak heights and what it shows.
Problem 11 Isoelectronic ions ★★★
Consider the ions F⁻, Na⁺ and Mg²⁺.1. Give the number of electrons in each.
2. Rank their radii from largest to smallest.
3. Finally, explain the ranking.
Problem 12 Ionisation energy exceptions ★★★
IE₁ values (kJ/mol): Mg 738, Al 578; N 1402, O 1314.1. Explain why Al is lower than Mg.
2. Then explain why O is lower than N.
Problem 13 Transition-metal ions ★★★
Write the configuration and the number of unpaired electrons for each ion.1. Fe³⁺
2. Zn²⁺
3. Cu⁺
Problem 14 Kinetic energy of photoelectrons ★★★
X-ray photons of energy 1500 eV strike aluminium. The binding energies are 118 eV (2s) and 73 eV (2p).1. State the equation linking photon energy, binding energy and kinetic energy.
2. Then calculate the kinetic energy of an electron from the 2s subshell.
3. Finally, calculate the kinetic energy of an electron from the 2p subshell.
Problem 15 Ionisation energy across period 3 ★★★
The graph shows IE₁ for sodium to argon.1. Describe the general trend.
2. Then explain the dip at aluminium.
3. Finally, explain the dip at sulfur.
Problem 16 Force between ions ★★★
The distance between Na⁺ and Cl⁻ in a crystal is 2.76 × 10⁻¹⁰ m. Use k = 8.99 × 10⁹ N·m²/C² and e = 1.602 × 10⁻¹⁹ C.1. Calculate the force between the ions.
2. Then calculate the force between Mg²⁺ and O²⁻ at 2.10 × 10⁻¹⁰ m.
3. Finally, calculate the ratio of the two forces and connect it to melting point.
Problem 17 Ranking ionisation energies ★★★
Rank Li, Na, K, Be and Mg by first ionisation energy, highest to lowest.1. Give the ranking.
2. Then justify the order within group 1.
3. Finally, justify why Be and Mg are above their group-1 neighbours.
Problem 18 Interpreting a sulfur spectrum ★★★
A spectrum has peaks at 2472, 229, 165, 23 and 10.4 eV with relative heights 2 : 2 : 6 : 2 : 4.1. Give the configuration and the element.
2. Then predict how the 1s peak would shift for chlorine.
3. Finally, explain why the shift happens.
Problem 19 Why two electrons then a jump? ★★★
IE₁ and IE₂ for sodium are 496 and 4562 kJ/mol. For magnesium they are 738 and 1451 kJ/mol.1. Explain why IE₂ is much larger than IE₁ for sodium.
2. Then explain why IE₂ for magnesium is only about twice IE₁.
3. Finally, predict whether IE₃ for magnesium is larger or smaller than 4562 kJ/mol.
Problem 20 Paragraph argument ★★★
Write a paragraph explaining why the radius decreases from Na to Cl but increases from Li to Cs.1. Use Coulomb’s law in your argument.
2. Mention nuclear charge, shielding and shell number.
