WATER

Water is one of our most plentiful chemicals (Chemical name: Dihydrogen Oxide). Its chemical formula, H₂0, is probably the most well known of all chemical formulas. The formula H₂0 tells us that one molecule of water is comprised of 2 atoms of hydrogen and one atom of oxygen bonded together. The bonds which hold the hydrogen and oxygen together are called covalent bonds - they are very strong.

Let's look at a picture of a molecule of water: In this picture the two hydrogens are represented by white spheres and the oxygen by a red sphere.

Why does the water molecule look bent?

The water molecule maintains a bent shape (bent at 107.5 degrees actually) because of two considerations. First the tetrahedral arrangment around the oxygen

and Second the presence of lone pair electrons on the oxygen.

What are Lone Pair Electrons?

These are the electrons that are not involved in the covalent bonds. The pairs of electrons are left alone. In our picture they are represented by the double dots. These lone pairs are very negative - containing two negative electrons each - and want to stay away from each other as much as possible. These repulsive forces act to push the hydrogens closer together

The lone pairs are negative - Are the Hydrogens positive?

The hydrogens are slightly positive. They get this way because of the "electronegativity" of oxygen. Electronegativity is a measure of how much one atom wants to have electrons, and oxygen wants to have electrons more than hydrogen does. Oxygen has a higher electronegativity. Because of this difference in electronegativity, the electrons in the covalent bonds between oxygen and hydrogen get pulled slightly toward the oxygen. This leaves the hydrogens a little bit electron-deficient and thus slightly positive. We can draw this polarization like this:

Images courtesy of South Bank University, London

Author: Tug Sezen