Video Transcript
Nitric acid, HNO3, is a fascinating
molecule because it has an unusual set of covalent bonds. Which of the following
dot-and-cross diagrams correctly depicts how bonding electrons are arranged in
nitric acid molecules?
A covalent bond forms when two
nonmetal atoms share one or more pairs of electrons. To see how the bonds form, we need
to look at the electrons. The nitrogen atom in the nitric
acid molecule contains five valence electrons, represented by blue crosses, all of
which take part in bonding. With one oxygen atom that is bonded
to a hydrogen atom, the nitrogen atom forms a single covalent bond. With a second oxygen atom, it forms
a double covalent bond.
Nitrogen has two valence electrons
remaining, but it forms a single bond to an oxygen atom. So, unlike the other bonds, which
are just covalent bonds, the final nitrogen–oxygen bond is a specific type of
covalent bond, called a coordinate covalent bond. A coordinate covalent bond is a
covalent bond where the pair of electrons forming the bond is donated from one atom
only. In this case, the pair of valence
electrons come from the nitrogen atom.
Hence, the dot-and-cross diagram
correctly depicting the arrangement of bonding electrons in a nitric acid molecule
is option (A).
