September 28-October 2, 2009
Solutions – Chapter 9
Page 1 of 4
The following problems (1-8) are based on material from Chapter 9.
What is the general electronic configuration (where
= principal quantum number)
that best describes the halogens as a group.
C. The halogens are characterized by having 5 electrons in the p
subshell, in the
ground state. For more information check Petrucci’s Section 9-2.
2. a) Which of the following gaseous atoms is
: P, Cl, Ca, or Si?
The atoms Si, P, and Cl are in period 3; Cl is the smallest of these three, since size
decreases across a period (as effective nuclear charge increases).
Ca is in period 4, and is larger than any of the above-named three atoms.
Cl is the smallest
b) Which of the following gaseous atoms has the
highest ionization energy
: Li, Ne, Na, Ar?
Ne has the highest ionization energy.
The noble gases have very high ionization energies and
the alkali metals have the lowest ionization energies (general trend: ionization increases across
a row, with some exceptions). Also, I.E.(Ne) > I.E.(Ar), since the valence electrons of Ne are
closer to the nucleus. In both Ne and Ar the core charge is +8.
3. Arrange the following gaseous ions in the order of
decreasing ionic radius (from largest
radius to smallest radius)
where > means "larger than".
All four of these species have the electron configuration [Ne] 3s
, thus they are all
isoelectronic with Ar.
For such an isoelectronic series the only difference is the charge on the
The higher the nuclear charge, the smaller the size, since there is a greater attraction
for the electrons.
The nuclear charges (atomic numbers, Z) for S, Cl, K and Ca are 16, 17, 19
and 20 respectively. S
is the largest, Ca
is the smallest.