Video Transcript
A single water molecule consists of
two hydrogen atoms and one oxygen atom. Which of the following statements
explains why water is a polar molecule? (A) Hydrogen atoms are much smaller
than oxygen atoms. (B) There is a big difference in
electronegativity between hydrogen atoms and oxygen atoms. (C) Intermolecular forces known as
hydrogen bonds exist between water molecules. (D) The electronegativity of
hydrogen atoms and that of oxygen atoms is very similar. (E) There are more hydrogen atoms
than oxygen atoms within each water molecule.
A polar molecule is a covalent
molecule in which one end of the molecule is slightly positive while the other end
is slightly negative. The partial charges in a polar
molecule are due to a difference in electronegativity between the elements in the
molecule. Electronegativity measures how
strongly an atom attracts an electron pair from a chemical bond. Oxygen is more electronegative than
hydrogen. So, the oxygen atom more strongly
attracts the electrons in the shared bond than hydrogen.
This means that the electrons in
the bond are closer to the oxygen atom than they are to the hydrogen atom. This results in the oxygen atom
being slightly negative while the hydrogen atoms are slightly positive. These permanent partial charges due
to the large difference in electronegativity between hydrogen atoms and oxygen atoms
are why water molecules are considered polar.
So, the statement that explains why
water is a polar molecule is statement (B): there is a big difference in
electronegativity between hydrogen atoms and oxygen atoms.
