Video Transcript
Which of the following bonds is
considered polar? A Br-Br single bond, a CH single
bond, a CC single bond, an OH single bond, or an OO double bond.
Bonds are polar due to differences
in electronegativity between atoms. This is because electronegativity
describes a tendency of an atom to attract shared electrons in a bond towards
itself. This means that if one atom is more
electronegative than the other, the electrons will be attracted towards the more
electronegative atom. When this happens, the bond is
considered to be polar. So, from this explanation, we know
that there needs to be a difference in electronegativity between the atoms, which
means that any bond that has between two atoms that are the same isn’t going to be
polar because there’s no electronegativity difference between the atoms.
So, we can safely rule out the
Br-Br single bond, the carbon-carbon single bond, and the oxygen-oxygen double
bond. This leaves us with the
carbon-hydrogen single bond and the oxygen-hydrogen single bond. Now, it might seem that perhaps
both of these bonds should be polar since there will be some difference in
electronegativity between carbon and hydrogen and oxygen and hydrogen.
If we look at the Pauling scale for
electronegativities, a common scale used to compare the electronegativities of atoms
ranking them from zero to four with four being the highest, we can see that while
there’s a pretty large difference in electronegativity between the oxygen and the
hydrogen, there’s not that large of a difference between the carbon and
hydrogen. Because the difference in
electronegativities here are so small, the carbon-hydrogen bond is generally not
considered to be polar, but the oxygen-hydrogen bond most certainly is. So, of our list, the bond that is
considered to be polar is the oxygen-hydrogen bond.
