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Ionization energies and photoelectron spectra

ChemistryAtomic Structure & Periodic TableAges 15–16

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A log-scale chart of the successive ionization energies of any element from H to Ca shows the big jump when an electron is removed from an inner shell, so you can deduce the number of outer electrons and the group. The First ionization energy screen shows the trend across Periods 2 and 3 (with the dips at B, Al and O, S explained with orbital boxes) and down a group; the Photoelectron spectrum screen draws one peak per subshell with a height proportional to its electrons; the Hydrogen spectrum screen finds the ionization energy from the convergence limit of the Lyman series.

Lesson: Ionization energies, electron configuration, photoelectron spectroscopy and the hydrogen emission spectrum

What it shows

Successive ionization energies always increase, but they jump sharply when the next electron comes from a shell closer to the nucleus, which is evidence for electron shells. Across a period the first ionization energy rises with nuclear charge, with dips where a new p subshell starts and where p electrons first pair; down a group it falls as the outer electron is further away and more shielded. A photoelectron spectrum shows one peak per subshell. The hydrogen convergence limit gives IE = hν∞. Data: NIST ionization energies for gaseous atoms and ions; PES values are rounded averages.

How to use

Choose a screen. On Successive ionization, move the Element slider or use ◀ ▶, untick Logarithmic scale to compare, and tap a bar. On First ionization, pick a period or group in Show and tap a point. On Photoelectron spectrum, tap a peak or press Mystery spectrum and change the element until the spectra match. On Hydrogen spectrum, change Lines measured and read the table.

Parameters you can change

  • Screen Successive ionization energies, First ionization energy across periods and down groups, Photoelectron spectrum (PES), Hydrogen spectrum and the convergence limit
  • Atomic number Z (1 = H … 20 = Ca) 1–20
  • Logarithmic scale for ionization energy
  • First ionization energy view All elements Z = 1–56, Period 2, Period 3, Group 1, Group 2, Group 17, Group 18
  • Number of Lyman lines measured 3–10

Questions to explore

  1. Why is the jump between the first and second ionization energies of sodium so large?
  2. Why is the first ionization energy of oxygen lower than that of nitrogen?
  3. How would the photoelectron spectrum of magnesium differ from that of sodium?

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