The Properties of Water

Water has several properties that make it different from other compounds.

Polarity - Water molecules are made up of hydrogen and oxygen atoms which are bonded together by a polar covalent bond.  What a covalent bond means in this case is that electrons are being shared between one oxygen atom and two hydrogen atoms.  It is known as a polar bond because the oxygen atom is larger than the hydrogen atoms so it's using a little bit more of the shared electrons.  This makes the oxygen atom slightly negatively charged and the hydrogen atoms slightly positively charged.

Cohesion - Water molecules are attracted to other water molecules and they often form hydrogen bonds between each other.  This attraction is called cohesion.  In a hydrogen bond, the slightly positively charged hydrogen atoms in one water molecule bond with the slightly negatively charged oxygen atoms from different molecules.  They bond together because they are oppositely charged.  This cohesion is why water droplets form.

Adhesion -  Water molecules are not only attracted to each other but also to the molecules of other compounds.  For example when a straw is placed in a glass of water, the water will rise up the straw above the level of the water in the glass.  This is because the water molecules on the inside edge of the straw are attracted to the straw molecules and then other water molecules come along because of cohesion and their hydrogen bonds.

Surface Tension - At the surface of water (and throughout it) the molecules form hydrogen bonds and adhere to each other.  In order to break these bonds, energy is required so unless energy is applied, then the hydrogen bonds will remain intact.  For instance, when a glass is filled to the brim with water and a little bit more is added it wont spill over the edge because there isnt enough energy being applied.  Another example involves a paper clip.  Normally a paper clip would sink in water but if placed evenly on the surface it will remain at the top.  This is because the paper clip is light enough to not have enough pressure or energy to pierce the strong surface tension caused by adhesion.

Specific Heat - This is the amount of energy required to heat required to raise the temperature of 1 gram of a substance up 1˚C.  Water has a particularly high specific heat so this means that it takes a long time for it to heat up or cool down.  This is why pools, lakes and the ocean are good ways to cool off on hot days because the water doesnt have enough time to get really warm as it sits in the sun.  This also why the time of year when oceans are hottest is the fall because during the summer they slowly heated up and by the fall they haven't cooled down yet and are very slowly loosing heat.

Ionization - This is when water molecules decompose into ions.  The polar covelent bond between two hydrogen atoms and one oxygen atom splits into a positively charged hydrogen ion and a negatively charged  hydrogen and oxygen ion.  This ionization process is constantly happening to water as is the process of the ions bonding back into molecules.

pH - Based on the ionization of water, there are the same amount of positively charged hydrogen ions as negatively charged  hydrogen and oxygen ions, therefore water has a completely neutral density of seven and is neither acidic or basic.

Universal Solvent - The fact that water is constantly ionizing makes water a very good solvent in which many substances will dissolve because when a compound is placed in water the strong ions (decomposed molecules) are able to decompose the atoms of the molecules of the solute.

States or Phases - Water is one of the few substances that can be found in all three states or phases in the natural world (without man-made technology).

Density - The density of water in its liquid state is one gram per milliliter.  The density of most substances (maybe all) in solid form is more than the density in liquid form.  Unusually, water has a lesser density when it is in its solid than in liquid form because when it changes to a solid the polar covalent bonds stabilize and spread out into lattice bonds.  The formation of the molecules in lattice bonds when water is in solid form is shown to the right in the picture above while on the left, the molecule formation of water in liquid form is shown. This means that with the same mass, a sample of water takes up more space in solid form than in liquid form.  Because water has a lesser density in solid form than in liquid form, solid water (ice) floats on liquid water.