49 . B
The atomic weight of an element depends on the number of protons and neutrons in its
nucleus; those numbers are always unique to a particular element, regardless of the number
of electrons in the species. The ionization potential depends chiefly on the radius of the parent
atoms and the effective charge of the nucleus. Since K+ and Cl– have different numbers of
protons by definition, they will have different effective charges, different atomic radii, and
therefore different ionization potential. Choice B, however, says that the two ions have the
same electronic configuration. Chlorine belongs to the third period and potassium belongs to
the fourth, so in their unionized forms, chlorine’s third shell contains seven electrons and
potassium’s fourth shell contains one electron. If chlorine gains one electron and potassium
loses one electron, both will have eight electrons in the third shell, which becomes the valence
shell. So, the potassium and chlorine ions described in the question both contain the same
number of electrons and the same number of occupied orbitals and thus share the same
electronic configuration.50 . E
Cl– has the largest ionic radius. When an atom gains an electron, positive protons in the
nucleus cannot hold on to the electrons as well and therefore the electron shells are able to
spread farther out.
51 . D
The balanced equation looks like this:
8H+ + MnO 4 – + 5Fe2+ → Mn2+ + 5Fe3+ + 4H 2 O.
One Mn2+ and five Fe3+ yield a total charge of +17.52 . D
The balanced equation looks like this: