http://www.ck12.org Chapter 3. Chemical Interactions
3.9 Hydrogen Bonding
- Describe hydrogen bonds and explain why they form.
- Relate hydrogen bonding to melting and boiling points of compounds.
The colorful red and blue model in the opening image represents a water molecule. The molecule’s one oxygen
atom is colored red, and its two hydrogen atoms are colored blue. Can you guess why? The red color represents
negative electric charge, and the blue color represents positive electric charge. The colors show that water is a polar
compound.
What Are Polar Compounds?
Polar compounds, such as water, are compounds that have a partial negative charge on one side of each molecule and
a partial positive charge on the other side. All polar compounds contain polar bonds (although not all compounds
that contain polar bonds are polar.) In a polar bond, two atoms share electrons unequally. One atom attracts the
shared electrons more strongly, so it has a partial negative charge. The other atom attracts the shared electrons less
strongly, so it is has a partial positive charge. In a water molecule, the oxygen atom attracts the shared electrons
more strongly than the hydrogen atoms do. This explains why the oxygen side of the water molecule has a partial
negative charge and the hydrogen side of the molecule has a partial positive charge.
Q:If a molecule is polar, how might this affect its interactions with nearby molecules of the same compound?
A:Opposite charges on different molecules of the same compound might cause the molecules to be attracted to each
other.