The first three ionization energies (in kJ/mol) of a third-period element are: 496, 4562, and 6912. To which element do these ionization values most likely belong?

• A. Na
• B. Si
• C. Mg
• D. Al

Answer: (A)

Verified step by step guidance

1. Understand that ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first ionization energy corresponds to removing the first electron, the second ionization energy to removing the second electron, and so on.
2. Look at the given ionization energies: 496 kJ/mol, 4562 kJ/mol, and 6912 kJ/mol. Notice that the first ionization energy is relatively low, but the second ionization energy is much higher, indicating a large jump.
3. Recall that a large jump in ionization energy typically occurs after removing all valence electrons, because removing an electron from a stable, noble gas-like core requires significantly more energy.
4. Identify the element by comparing the pattern of ionization energies to the electron configuration of third-period elements (Na, Mg, Al, Si). Sodium (Na) has one valence electron, so the first ionization energy is low, but the second ionization energy is very high because it involves removing an electron from a full neon core.
5. Conclude that the element with a low first ionization energy followed by a large jump to the second ionization energy is sodium (Na).