Video Transcript
Ammonia boron trifluoride molecules
are formed when an ammonia molecule donates a bonding pair of electrons to a boron
trifluoride molecule. The structure of the ammonia boron
trifluoride molecule is shown below. Which of the following statements
correctly describes the ammonia and boron trifluoride molecules during the formation
of the ammonia boron trifluoride molecule? (A) The boron trifluoride and
ammonia molecules both act as a Lewis acid. (B) The boron trifluoride and
ammonia molecules both act as a Lewis base. (C) The boron trifluoride molecule
acts as a Lewis base and the ammonia molecule acts as a Lewis acid. Or (D) the ammonia molecule acts as
a Lewis base and the boron trifluoride molecule acts as a Lewis acid.
Ammonia boron trifluoride is an
example of a compound where a coordinate bond is formed between two molecules:
ammonia and boron trifluoride. A coordinate covalent bond is a
covalent bond where the pair of electrons forming the bond is donated from one atom
only. In the case of ammonia boron
trifluoride, the donor atom is the nitrogen atom of ammonia and the acceptor atom is
the boron atom of boron trifluoride. The prerequisite to becoming a
donor atom in this type of bonding is to have a surplus of electrons that can be
donated. The acceptor atom, on the other
hand, has a scarcity of electrons and so receives them. Nitrogen is the donor atom as it
has a lone pair of electrons, which makes it electron rich. Boron is the acceptor atom as it
has an empty p orbital, which can receive a pair of electrons.
In this molecule, the nitrogen of
ammonia donates both the bonding electrons to the boron of boron trifluoride,
forming a coordinate bond, which leads to the formation of ammonia boron
trifluoride. As ammonia donates a pair of
electrons, we can call it a Lewis base. This is because a Lewis base is
defined as a substance that can donate a lone pair of electrons, forming a bond. This makes boron trifluoride a
Lewis acid. A Lewis acid is a substance that
can accept a lone pair of electrons, forming a bond.
Let’s bring back the answer
choices. We now know that the correct answer
is (D). The ammonia molecule acts as a
Lewis base and the boron trifluoride molecule acts as a Lewis acid.
