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Unique Characteristics of Water

Of all the molecules that are common on earth, only water
exists as a liquid at the relatively low temperatures that
prevail on the earth’s surface, three-fourths of which is
covered by liquid water

The Atomic Structure of Water

Water has a simple atomic structure. It consists of an oxygen
atom bound to two hydrogen atoms by two single covalent
bonds.

Even though the total charge on a water molecule is neutral, the charge is unevenly distributed across the water molecule. Because of this uneven distribution of charge water is called a polar compound.

The two hydrogen atoms bond with the single oxygen atom at an angle (104,5⁰)

Hydrogen Bondings

Molecules that exhibit charge separation are called polar molecules and water is one of the most polar molecules known.

Polar molecules interact with one another, these interactions involve hydrogen atoms, they are called hydrogen bonds.

Water is a powerful solvent!

Water is an effective solvent because of its ability to form hydrogen bonds. Water molecules gather closely around any substance that bears an electrical charge, whether that substance carries a full charge (ion) or a charge separation (polar molecule).

Every time a sucrose molecule dissociates or breaks away from the crystal, water molecules surround it in a cloud, forming a hydration shell and preventing it from associating with other sucrose molecules. Hydration shells also form around ions such as Na+ and Cl–

Water Clings to Polar Molecules

The polarity of water causes it to be attracted to other polar molecules.

When the other molecules are also water, the attraction is referred to as cohesion.

When the other molecules are of a different substance, the attraction is called adhesion.

The cohesion of liquid water is also responsible for its surface tension.

Small insects can walk on water because at the air-water interface all of the hydrogen bonds in water face downward, causing the molecules of the water surface to cling together.

The attraction of water to substances like glass with surface electrical charges is responsible for capillary action.

Water Stores Heat

Water moderates temperature through two properties:

1. its high specific heat and
2. its high heat of vaporization

Water is said to have a high specific heat, which is defined as the amount of heat that must be absorbed or lost by 1 gram of a substance to change its temperature by 1 degree Celsius (°C).

Specific heat measures the extent to which a substance resists changing its temperature when it absorbs or loses heat.

A considerable amount of heat energy (586 calories) is required to change 1 gram of liquid water into a gas.

Hence, water also has a high heat of vaporization.

Many organisms dispose of excess body heat by evaporative cooling; for example, humans and many other vertebrates sweat.

Density of Ice

Unlike most solids, solid water is less dense then liquid water. This property is due to the shape of the water molecule and hydrogen bonding.

Because ice floats on water, pond and lakes freeze from the top down not the bottom up. Ice insulates the water below from the cold air, which allows fish and other aquatic creatures to survive under the icy surface.