Practice Quiz

SAT Chemistry

Category - Multiple Choice

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The following list shows the ionization energies for sodium (Na) in order from first to fourth ionization energies:

495.8 kJ/mol; 4562.4 kJ/mol; 6912 kJ/mol; 9543 kJ/mol.

Compare it to the same list for Magnesium and explain why the second ionization energy for Magnesium is much lower than the second ionization energy of sodium.

In order from first ionization energy to fourth for Magnesium: 737.7 kJ/mol; 1450.6 kJ/mol; 7732.6 kJ/mol; 10,540 kJ/mol.
  1. Magnesium is a metal, and they always have lower second ionization energies. Sodium is a salt, so it doesn’t give away more than one electron.
  2. Magnesium is always a +2 ion, so the energy required to give away two electrons is low.
  3. By giving away one electron, Na reaches a noble gas configuration, so giving away a second electron takes a lot of energy.
  4. Since it has two electrons to give away before reaching noble gas configuration, the second ionization energy of Magnesium is low.
  5. Both C and D.
Explanation
Answer: E. It’s extremely hard for sodium to give up that second electron and become Na+2; Magnesium, on the other hand, has a noble configuration as Mg+2. Thus, it takes less energy for the second ionization of Magnesium.
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