The Chemistry of Water

OK, so in my last blog I said Water was an amazing compound. What makes it so amazing? Today I will look at some of the unusual chemical properties of Water.

Chemically Water is H₂O. Another chemical name is Hydrogen Oxide. In the Water molecule the Oxygen is more electronegative than the Hydrogen. When the two Hydrogen atoms and the Oxygen atom form the covalent bonds in the Water molecule, the Oxygen side of the molecule has a partial negative charge and the Hydrogen side a partial positive. This is due to the movement of the unmatched electrons in the Oxygen away from the Hydrogen atoms. This contributes to the formation of Hydrogen Bonds. The hydrogen bonds found in Water are the foundation of many of the unique properties that make it a miracle molecule.

Water is the consummate molecule for hydrogen bonds. Each positive Hydrogen atom in one Water molecule creates a hydrogen bond with an Oxygen atom in a different molecule. Each Water molecule can form four hydrogen bonds, one with each Hydrogen atom and two with each Oxygen. Water is exceptionally uncommon when compared to other, similar chemicals formed by the atoms surrounding Oxygen on the periodic chart. Water is a liquid at standard temperature and pressure; other analogous hydrides of the Oxygen family, such as Hydrogen Sulfide (H₂S) are gases. All basic Hydrogen compounds formed with the elements surrounding Oxygen in the Periodic Table (HF - Hydrofluoric acid, NH₃ - Ammonia, and CH₄ - Methane) are also gases. This is due to the stronger hydrogen bonds in Water that increase the energy requirements to produce Water Vapor.

The polarity of the Water molecule also makes it exceptionally qualified to be classified as the universal solvent. Almost any molecule with a slightly charged or ionized group can be hydrated by Water. Even large, complex molecules like DNA or proteins can be hydrated. But some things don't mix, like Water and Oil. Oils or fats, as pure hydrocarbons, lack polar groups but fatty acids, a hydrocarbon with a carboxyl group (-COOH), can be dissolved or are at least miscible with water. Using such an emulsifying agent, Water and Oil can be mixed in varying proportions to create creams, lotions and ointments.

This reaction between Water and fatty acids is how soap works. Soap is a salt of a fatty acid. The hydrocarbon chain end of the soap molecule acts to dissolve or emulsify the oils on our skin or in the substances we are washing off. The Water from the showerhead hydrates the ionized carboxyl end of the soap molecule and allows the oils to be washed down the drain.

Stearic Acid, a component of Soap (each bend is a Carbon-Hydrogen group CH₂)

Water can react with both acids and bases since it ionizes to a small extent into H⁺ and OH^- ions. The H⁺ ions are hydrated as H₃O⁺. In chemistry, pH is a measurement of the acidity or basicity of an aqueous solution. Values greater then seven are considered basic and values less than seven are acidic. Pure Water has a pH of seven.

The last exceptional property we will look at today is that water exists in all three phases - solid, liquid and gas - at natural ambient temperatures. The Hydrogen bonding in Water contributes significantly to this property but the shape of the water molecule due to the electron shift also plays a part. Water is bent at almost the perfect angle to produce a hexagon or honeycomb when in a solid state.

Next we will look at some of Water's physical properties and why ice floats.

Water was one of the first things God created, even before He said “Let there be Light”. "Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters. Genesis 1:2 (NIV)"