A plot of first-ionization energy versus atomic number reveals that the value for…
CHEMISTRY · Single correct · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
A plot of first-ionization energy versus atomic number reveals that the value for aluminum (Z=13) is lower than that for magnesium (Z=12), even though aluminum has a higher nuclear charge. Which of the following statements best explains this observation?
(a) The filled 3s subshell in Mg is especially stable, so removing one of these electrons requires more energy than removing an electron from the less stable configuration of Al.
(b) Because Al has more protons, its valence electron experiences a larger effective nuclear charge, which explains why Mg shows the higher first-ionization energy.
(c) The electron removed from Al is in a 3p subshell that is higher in energy and more shielded than the 3s electron removed from Mg.
(d) Greater electron–electron repulsion among Al’s valence electrons lowers the energy needed to remove one, leading to Al’s smaller ionization energy.