Video Transcript
Which of the following molecules
would you predict is unlikely to form a coordinate covalent bond with a metal ion in
solution? Assume no bonds on the molecule are
broken. (A) CH4, (B) H2O, (C) CO, (D) Br1-,
or (E) NH3.
Coordinate covalent bonds are
unusual types of covalent bonds. All of the bonding electrons are
from one atom rather than both as we see in a conventional covalent bond. The coordinate covalent bond forms
when one atom effectively donates a lone pair of electrons to the other atom.
A common example of this is when
water molecules form coordinate covalent bonds with metal ions in a solution. Water molecules can form coordinate
covalent bonds with a metal ion because the oxygen in water has lone pairs of
electrons. Lone pairs from the oxygen atoms in
water can be donated to the metal ion to form a complex. Often, metal ions can form many
coordinate covalent bonds by accepting multiple lone pairs of electrons. A coordinate covalent bond can be
represented as an arrow, with the species shown at the arrowhead representing the
electron pair acceptor and the species at the base representing an electron pair
donor.
Let’s have a look at the Lewis
structures for our answer choices to determine which species does not have lone
pairs of electrons. Species that do not have lone pairs
of electrons are unlikely to form a coordinate covalent bond with a metal ion. We can thus identify which species
cannot be an electron pair donor to find the correct answer to this question.
We can draw the Lewis structures of
answer choices (A) through (E). We can see that of the answer
choices, the only structure that does not have lone pairs would be answer choice
(A), or methane. Methane would be unlikely to form a
coordinate covalent bond with a metal ion in solution due to its lack of lone pairs
of electrons. Therefore, the correct answer is
answer choice (A), CH4.