Water Cohesion, simply put, means that water molecules

Water has extraordinary propertieswhich makes it vital to life on earth. The earth is composed of 75% water andin living cells, 75%-90%. Because of the slight 4.5 degrees difference inwater’s expected 109.5 degrees tetrahedral structure, the polar molecule, waterhas some amazing properties which makes it evident that life of earth isdependent of its presence. Hydrogen bonding, Cohesion, Surface tension,Adhesion, Capillarity Action, Freezing and Density, Heat Capacity and being anexcellent solvent are some of the properties which demonstrates the importanceof liquid water.Hydrogen bonding is possible sincewater is known to be a polar molecule that is, having two charges; oxygen beingof a slightly negative charge and hydrogen a slightly positive. Because of thisand oxygen’s high electronegativity, that is, it’s high affinity for electrons,the electrons are tend to be shared unequally, hence, bringing forth it’spolarity.

Due to the hydrogen bonds, water molecules can bond to othersurrounding water molecules. The hydrogen bonds are weak since bonds areconstantly breaking and forming.As a result of water molecules’polarity and ability to hydrogen bond it is known to be cohesive. Cohesion,simply put, means that water molecules are able to adhere to other watermolecules. Because of water’s cohesiveness the inter-related property of surfacetension is recognized.At the surface of water there arefewer water molecules to cohere with and hence, the bonds among those moleculesthat do come into contact with one another create a layer of strongly bondedwater which makes a bit difficult to penetrate since it creates an invisiblebarrier of the water from the atmosphere.Another amazing property of water isadhesion.

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Water is attracted to other molecules via adhesive forces, that is,attractive forces between molecules of one kind and molecules of a differentkind. Water molecules adhere to other substances as a result of its polarity.Example: Water in a glass; the water molecules adhere to the molecules of theglass.As a result of adhesion and cohesion,water is able to move to very high heights defying gravity until the force ofgravity overpowers it, this is called capillary action.

In capillary action theforces of cohesion are strong but the forces of adhesion are stronger and hencethe liquid is able to move upwards by being attracted to the walls of the tubee.g. When a nurse is taking a sample of your blood for a test, after prickingthe finger she uses a capillary tube to collect a sample of the blood (N.B. bloodis made up of about 90% water), it is noticed that the blood goes up the tube.This is because of the higher attraction of the water molecules to the capillarytube molecules. Another example is the transportation of water to all parts ofthe plants through the xylem; water molecules are attracted to the walls of thexylem and the water keeps moving upwards due to capillary action and thetransportation of the products of photosynthesis via the phloem which is aidedby water.

Mostsubstances in their solid form tends to be more dense than when it is in itsliquid form, in the case of water it is the complete opposite. In liquid waterthe hydrogen bonds are not fixed, the molecules are free to move around and itis usually flat or two dimensional but, in ice a crystalline structure isformed, hydrogen bonding to four other molecules in a three dimensionallattice, having space between and hence, being less dense. Because liquid wateris more dense than ice, it allows for the continuation of aquatic life even invery cold temperatures by making the ice float at the top and because of itswhite colour, it is able to reflect light and hence continuing life below theice since animals are able to survive in the liquid water below the ice.Wateralso, has a high specific heat capacity. This is the amount of heat energyrequired to raise the temperature of one kilogram of water by one degree celsius.Water absorbs a lot of thermal energy before it is converted to another state,and for this reason it is the medium of life since it is able to regulate andminimize the change in temperature.

E.g. on a very sunny day, the temperatureon land increases but in the water has a very low temperature change, and hencewater’s ability to absorb heat is seen. Water is used by warm-bodies animals todispense heat around the body by moving it from warm places to cool places.Wateris known to be an excellent solvent which means that other substances candissolve in it to form solutions.

A major and important example is the processof transportation and excretion in the human body. Water transports all theessential nutrients in easy to absorb form and also, all the waste productsmust be excreted from the body to prevent toxic build-up. By examining few of these uniqueproperties of water we begin to appreciate its presence since without it wewould never be present on earth.


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