Summary
Highlights
Water is a polar molecule because electrons are shared unequally between the oxygen and hydrogen atoms. Oxygen is highly electronegative, pulling electrons closer to itself, resulting in a partial negative charge on the oxygen and partial positive charges on the hydrogen atoms. This creates a dipole, similar to a magnet with positive and negative poles.
Due to its polarity, water molecules orient themselves so that the positive hydrogen of one molecule is attracted to the negative oxygen of another. These attractions are called hydrogen bonds. These bonds dictate how water molecules interact with each other and other substances.
One key property resulting from water's polarity and hydrogen bonds is cohesion, which is the attraction between water molecules. This strong attraction is responsible for surface tension and allows large globules of water to form in space.
Water also exhibits capillary action, a combination of adhesion (water sticking to other surfaces with a charge) and cohesion (water molecules pulling each other along). This property is crucial for plants, as it allows water to move up tiny tubes like xylem in trees.
Water has a high specific heat, meaning it requires a lot of energy to change its temperature. This property helps moderate temperatures in environments like coastal cities (e.g., Seattle compared to Bozeman) and within living organisms, preventing drastic temperature fluctuations.
Unlike most substances, ice floats. As water cools, its hydrogen bonds form a three-dimensional matrix, decreasing its density. If ice sank, oceans would freeze from the bottom up, making life on Earth impossible.
Water's polarity makes it an excellent solvent. It can dissolve ionic compounds like salt by surrounding the individual ions with its charged ends. It also dissolves other polar molecules, like sugar, following the principle that 'like dissolves like'. Non-polar substances, like fats, do not dissolve in water.
Water's unique polar properties are fundamental for life on Earth. Its role as a solvent is vital for transporting materials within living organisms. The search for extraterrestrial life often focuses on the presence of liquid water, as seen with locations like Europa, a moon of Jupiter.