Properties of Water

• The main constituent of the oceans is of course , water. The presence of large amounts of liquid water on Earth’s surface over much of its history has resulted from a fortunate combination of factors.

• Among them are water’s unusually high freezing and boiling points for a molecule of its size and its relative chemical stability.

Water has other remarkable properties that contribute to the characteristics of oceans………from their ability to support life to effects on climate. Underlying these properties is water’s molecular structure.

The Water Molecule• A molecule of water

consists of two hydrogen atoms bound to one atom of oxygen. Crucial to formation of the bonds between the oxygen and hydrogen atoms are 4 tiny negatively charged particles called electrons, which are shared between the atoms.

• In addition, six other electrons move around within different regions of the oxygen atom. This electron arrangement makes the H2O molecule chemically stable but gives it an unusual shape. It also produces a small imbalance in the distribution of electrical charge within the molecule.

Covalent Bond

• An important result of this is that neighboring water molecules are drawn to each other by forces called Hydrogen Bonds.( 2 or more water molecules)

Three States of Water• The temperatures

at which water changes between the 3 states are high compared with substances having similarly sized molecules.

• For ice to melt and water to vaporize, high levels of energy are needed to break all the hydrogen bonds. Water is also unusual because its solid form is slightly less dense than its liquid form, so ice floats in liquid water.

• The reason for this is that the molecules in ice are loosely packed, whereas those in liquid water move around in snugly packed groups.

• The fact that ice floats on liquid water is important because it allows the existence of large areas of polar ice which affect heat flow between ocean and atmosphere and help stabilize ocean temperatures and Earth’s climate. Water is the only natural substance found in all 3 states at Earth’s surface!

Properties• High Boiling Point - 100 degrees C• Water stays in the liquid phase

most often and it is this form that accounts for over 85% of the mass of most marine organisms and serves as the medium in which the chemical reactions that support life occur.

• Low Freezing point- 0 degrees C. Because of the expansion of water after reaching its maximum density temperature of 4 degrees C, ice is less dense and floats

• Water will freeze from the top to the bottom. This unusual expansion of water is important to life because animals and plants can survive under ice.

• Heat Capacity- Water has a high heat capacity, which exceeds that of nearly all other known liquids. When heat is added to water most of the heat is used to break H bonds linking the molecules. Only a fraction of the energy increases the vibrations of the water molecules which are detected as a rise in temperature. This means that areas of the ocean can absorb and release huge amounts of heat energy with little change in temperature.

• It also means that movements of water---ocean currents transfer enormous amounts of heat energy around the planet; the role of ocean currents is vital to Earth’s climate. This property is very important to life because organisms need gradual changes

• Surface Tension- Water has a high surface tension; the surface molecules tend to be drawn together and inward toward the center of the aggregation of water molecules forming a skin that is resistant to disruption.

• This is vital to certain processes within living organisms----for example, water transport in plants and blood transport in animals. Surface tension also allows small insects such as the water striders to

• walk, mate and feed on the ocean surface.

• It also has a part in the formation of ocean waves. Surface tension is affected by temperature and increases with a decrease in temperature. The colder the water, the more H bonds form and the stronger the surface tension

• * Related to cohesion of water

Viscosity

• Viscosity- refers to the thickness of water and is influenced by the number of H bonds. The colder the water the more H bonds form so the more viscous the water. This affects swimming organisms.

• The more viscous the water, the harder it is to swim; organisms need more energy. Deep water animals don’t move much- too much energy.

Density• Density- defined

as mass per unit volume. Water density is high; 800X more than air. It is affected by salinity and temperature.

• The density of seawater is greater than the density of pure water at the same temperature. Fresh water will float on salt water. In addition, warm water will float on cold water.

Dissolving Power• Dissolving power-

Water is known as the universal solvent. More substances dissolve in water then any other common liquid. The polar nature of water makes it an excellent solvent.

• Disassociation

• This dissolving capability is important to life because water holds salts, nutrients, gases; everything needed to survive.

Transparency

• Transparency- the ability of water to transmit light. This is important for photosynthetic plants ; need to receive sunlight in order to grow.

Capillary Action• Capillary Action• Ability of water

to move against gravity; cohesion and adhesion of water molecules.