Question Video: Using Electronegativity to Explain Why Water Is a Polar Molecule Science • Second Year of Preparatory School

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.