Answers and Explanations
Spectroscopy, Light, and Electrons 14317.Calcium reacts with element Xto form an ionic
compound. If the ground-state electron configu-
ration of Xis ls^2 2s^2 2p^4 , what is the simplest
formula for this compound?
(A) CaX
(B) CaX 2
(C) Ca 4 X 2
(D) Ca 2 X 2
(E) Ca 2 X 3- E—This configuration represents a noble gas
(neon). The outer s and p orbitals are filled. - C—Transition elements have partially filled
d orbitals. This configuration is for the metal
zirconium. - B—The single electron in the s orbital indicates
that this is the very reactive alkali metal lithium. - A—The 1s orbital is not filled. One indication of
excited states is to have one or more inner orbitals
unfilled. - B—The electron configuration for iron is
ls^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2. To produce an iron(II) ion,
the two 4s electrons are removed first. - E—The elements that are normally diamagnetic
are those in the same columns of the periodic
table as Be, Zn, and He. All others are normally
paramagnetic. - A—The electron configuration for arsenic is
Is^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^3. The valence shell is
the outer shell (largest n). In this case the outer shell
electrons are 4s^2 4p^3. This means that n=4, and
that l=0 or 1. If l=0, then ml=0; and if l=1,
then ml=−l, 0, or +1. Finally, msmust be either
+^1 ⁄ 2 or −^1 ⁄ 2. - D—Halogens have a valence shell with s^2 p^5.
- B—Transition metals have partially filled d
orbitals (d^1 −^10 ), along with an s^1 or s^2. - A—The 1p orbital does not exist.
- C—The outer s electrons are not present in most
transition metal ions. - D—This is part of the Heisenberg uncertainty
principle. - E—The four electrons in the oxygen 2p orbitals
are arranged with one pair and two unpaired elec-
trons with parallel spins. This makes the oxygen
atom paramagnetic. This arrangement is due to
Hund’s rule. - A—The Pauli exclusion principle restricts the
number of electrons that can occupy a single
orbital. - B—The d orbitals are shielded more efficiently
than the s orbitals. Thus, the less shielded d
orbitals do not fill as readily as s orbitals with
similar energy. - D—The electron configuration of rubidium is
ls^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^1. This gives n= 5
and l=0 for the last electron. If l=0 then ml
must equal 0. The value of msmay be either +^1 ⁄ 2
or −^1 ⁄ 2 - A—Calcium will form a +2 ion (Ca^2 +), and X
will need to gain two electrons to fill its outer
shell and become a −2 ion (X^2 −). The simplest
formula for a compound containing a +2 ion and
a −2 ion would be CaX. The other answers
involve different charges or a formula that has
not been simplified.