Cohesion of Water Molecules

You can change the shape of a water ring because water molecules stick together by hydrogen bonds. A water molecule is made up of two hydrogen atoms and one oxygen atom. The oxygen atom is slightly electronegative and the hydrogen atom is slightly electropositive. Because opposites attract, the hydrogen (+ charge) of one water molecule will be attracted to the oxygen atom (- charge) of another water molecule. This type of a bond is called a hydrogen bond. A hydrogen bond is weak, about only 5% as strong as a covalent bond.

Hydrogen bonds are temporary, breaking and reforming in trillionths of a second. At any moment a sufficient number of hydrogen bonds are formed giving water its structure. Hydrogen bonds give structure to water and this is called cohesion.

• What are the different types of chemical bonds?
• What type of bond is formed by hydrogen and oxygen?
• Is the bond between oxygen and hydrogen a nonpolar or a polar bond? Why?
• At an instantaneous moment, how many other water molecules can one water molecule form temporary bonds with?
• Why is this hydrogen bonding important in the movement of water against gravity?
• If hydrogen bonds are so weak, why don't your DNA strands separate easily?
• What does cohesion have to do with surface tension?

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