Water is often referred to as the medium of life. It is an essential component to all forms of life – 65% of human body cells are made up of water, and some plants and animals are composed of up to 90% of water. Thus, water is an essential compound in the circle of life, which involves photosynthesis and cellular respiration through oxygen and water. Today we will take a more in-depth look at the details of water, including their polarity, and how they are bonded.
Polarity of Water
If a substance is polar, it has a magnetic polarity. Water is polar due to its two components – hydrogen and oxygen atoms. Electrons are unequally shared between these atoms since oxygen atoms are more attractive to electrons than hydrogen atoms. Due to the number of electrons that the atoms have, oxygen acquires a negative charge, and as a result, hydrogen atoms have a slightly positive charge. Thus, since water has both positive and negative charges, it acts like a magnet. This allows for the formation of hydrogen bonds, which form between negative oxygen atoms and positive hydrogen atoms. This ionic bond is relatively weak due to the partial charges in water molecules, but the attraction is enough to lead to significant outcomes.
Due to the polarity of water, other polar or charged compounds are attracted to water and form hydrogen bonds with them, causing the compounds to dissolve in water. These compounds are called hydrophilic (water-loving). Sugars and the majority of salts are typical examples of hydrophilic compounds. On the other hand, non-polar substances are not attracted to water; instead, they repel each other. Such compounds are called hydrophobic (water-hating) compounds. Good examples are fats and oils, which never mix with water regardless of the conditions.
The hydrogen bonds of water molecules are an excellent way of explaining the four properties of water: thermal, cohesive, adhesive, and solvent properties.
Thermal Properties of Water
Water can absorb a significant amount of heat before changing its state, because of its extensive hydrogen bonding between molecules that need to be broken before a change in state. As a result, water is an effective medium for organisms as it maintains constant conditions both internally and externally.
Methane is often compared with water because they show different thermal properties although they have similar size, weight, and valence structures. However, water is different from methane in that water is polar whereas methane is non-polar. Since water can form hydrogen bonds due to high electronegativity of oxygen atoms, it has a higher melting point and boiling point than methane. Thus water remains as a liquid over a wide range of temperatures, from 0 to 100 degrees. This is beneficial for most organisms since the temperature range of most habitats on Earth is between 0 and 100 degrees.
Water has a higher specific heat capacity, the energy required to raise 1ºC of 1g of substance, since hydrogen bonds restrict the movement of water molecules. The breaking of the hydrogen bonds needs energy, which requires large amounts of heat called the latent heat of vaporization. Because water has a high latent heat of vaporization (the energy absorbed per gram as it changes its state from liquid to gas), evaporation of water leads to a cooling effect.
Humans utilize these thermal properties of water through sweat. The evaporation of sweat requires an input of energy which comes from the surface of the hot skin. When sweat evaporates, it absorbs a lot of thermal energy from the skin due to the high specific heat capacity, which effectively cools body temperature. For this reason, water is an effective coolant.
The next post will cover content on water’s cohesive, adhesive, and solvent properties!
Works Cited
Allott, Andrew, and David Mindorff. Biology: Oxford IB Diploma Programme. Oxford University Press, 2014.
The Science Herald 
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