When a vast number of water molecules are mixing freely in the liquid form, the positive poles are attracted to the negative poles due to static electricity. This electrostatic attraction is termed a hydrogen bond. It is about 20 times weaker than the H – O bonds within any one water molecule, but still gives rise to considerable, transient adhesion, which packs the water molecules closely together in the liquid state.
In contrast, as the temperature falls below about 4 ° C and ice begins to form, the hydrogen bonds between the molecules become longer lived. They eventually settle into a rigid, rather open framework, comprising a stack of tetrahedrons, in which each oxygen atom is hydrogen-bonded to four surrounding oxygen atoms. The more open, rigid framework of ice fixes the oxygen atoms further apart than they tend to be, on average, in liquid water – which explains why ice is less dense than water.
At high temperatures, the hydrogen bonds offer considerable resistance to the separation of molecules that occurs during the formation of water vapour. Although some water molecules will spontaneously adopt the vapour form at all temperatures, water is nothing like as volatile as other similar molecules. This is fortunate, as it ensures the persistence of surface water in most climate zones typical of the Earth’s surface. It also explains why the wholesale conversion of water to vapour (i.e. by boiling to form steam, which is just the word for hot water vapour) occurs only at temperatures in excess of 100 ° C: far higher than would otherwise be expected for a molecule of its size and shape. Yet again, this proves crucial to the success of carbon-based life-forms.
Even when water reaches boiling point, the hydrogen bonds complicate steam formation: to change liquid water into steam at 100 ° C requires nearly seven times as much energy as would be needed to melt the same weight of ice at 0 ° C, and about five and a half times the energy required to raise the temperature of liquid water by 1 ° C. The ‘extra’ energy requirement needed to transform a substance from one form (or ‘phase’) to another, without increasing the temperature, is known as latent heat – and water has higher latent heat requirements than would be expected from similar molecules. This is again highly fortunate for living beings, as it is the basis for most of the strategies used to maintain body temperatures within healthy ranges.
In liquid water, hydrogen bonds are also manifest in the cohesion of water surfaces, known as surface tension. Although of limited importance to you and me, surface tension is integral to the lifestyle of pond skaters and other small insects that can literally walk on water, their weight insufficient to snap the hydrogen bonds beneath their feet.
Now, as you are aware of the power of water, feel yourself lucky to be a customer of Thames Water- the company that focuses on providing full-fledged water supply and sanitation services to its consumers. And, if you are still not using their services, call them directly at Thames Water Contact Number and get your water supply switched to the company.