The greatest molecule

What we particularly appreciate in water

[Deposit Photos]

In the 18th cen­tu­ry, An­toine Lavoisi­er ran an elec­tric cur­rent through wa­ter and dis­cov­ered two gas­es in its com­po­si­tion: hy­dro­gen and oxy­gen.

The for­mu­la of the wa­ter mol­e­cule is H₂O, two hy­dro­gen atoms and one oxy­gen atom. In this mol­e­cule, there is a par­tial pos­i­tive charge in the hy­dro­gen atoms, and a par­tial­ly neg­a­tive charge in the oxy­gen atom. This means that mol­e­cules can form bonds with each oth­er. These bonds are called hy­dro­gen bonds. It is the small size of the hy­dro­gen atom that al­lows the strong­ly po­lar­ized mol­e­cules of wa­ter to come to­geth­er quite close­ly to form these bonds. They are not as strong as the atom­ic bonds with­in the mol­e­cule (co­va­lent bonds), but be­cause of them wa­ter mol­e­cules are more strong­ly at­tract­ed to each oth­er than the mol­e­cules of al­most all oth­er sub­stances.

The hy­dro­gen bonds mean that wa­ter has a very high spe­cif­ic heat. A lot of en­er­gy is re­quired to heat wa­ter. Based on the lo­ca­tion of oxy­gen in the pe­ri­od­ic ta­ble and the boil­ing tem­per­a­tures of hy­drides (bonds with hy­dro­gen) of el­e­ments in the sub-group of oxy­gen (sul­fur, se­le­ni­um, tel­luri­um), wa­ter with­out hy­dro­gen bonds would boil and freeze at much low­er tem­per­a­tures, sim­i­lar to hy­dro­gen sul­fide which boils at -60 °С and freezes at -82.3 °С.


Boil­ing wa­ter

The hy­dro­gen bonds ex­plain cap­il­lary phe­nom­e­na. We can ob­serve them, for ex­am­ple, when paint ris­es be­tween the bris­tles of a brush. Wa­ter mol­e­cules are so strong­ly at­tract­ed to each oth­er that they over­come the pow­er of grav­i­ty. Through the cap­il­lar­ies that run through the tree, wa­ter trav­els from its roots right to the leaves.


A drop of wa­ter

Hy­dro­gen bonds give wa­ter its high sur­face ten­sion. This means that wa­ter can gath­er in drops, it can be poured into a cup “with a mound”, and some in­sects can walk on it as if it were sol­id ground.

A uni­ver­sal sol­vent

Hy­dro­gen bonds make wa­ter a uni­ver­sal sol­vent. It dis­solves salts, sug­ars, acids, al­ka­lis and even some gas­es. These sub­stances are called hy­drophilic (wa­ter-lovers) be­cause they evap­o­rate eas­i­ly in wa­ter.

On the con­trary, fats and oils are hy­dropho­bic. This means that their mol­e­cules are not ca­pa­ble of form­ing hy­dro­gen bonds. So wa­ter re­jects these mol­e­cules, pre­fer­ring to form bonds with­in it­self. To wash fat off our hands we use soap, which has mol­e­cules with hy­dropho­bic and hy­drophilic parts. The hy­dropho­bic parts at­tach to the fat, break­ing in into small drops. And with the hy­drophilic parts this struc­ture at­tach­es to the flow of wa­ter and goes with it down the drain.

Oil does not dissolve in water [Deposit Photos]

No two snowflakes are iden­ti­cal

First­ly, the small­est change in tem­per­a­ture and hu­mid­i­ty af­fects the form that wa­ter mol­e­cules freeze in. Sec­ond­ly, the av­er­age snowflake con­tains 10 quin­til­lion (10 with 18 ze­roes) wa­ter mol­e­cules. And this gives plen­ty of scope for cre­ativ­i­ty.

Wa­ter is prac­ti­cal­ly the only sub­stance that ex­pands when it is in a sol­id state. Usu­al­ly, sub­stances be­come com­pacter when they freeze, and take up less vol­ume than liq­uid forms. But in the case of wa­ter, ice is less dense, and so it is light than the same vol­ume of liq­uid wa­ter, which means that ice cubes float in the top lay­ers of our drinks. And, more im­por­tant­ly for liv­ing or­gan­isms, ice in wa­ter bod­ies also forms on top, and does not let the re­main­ing wa­ter freeze. When they freeze, wa­ter mol­e­cules form an or­dered lat­tice, tak­ing up more space than they re­quired in a liq­uid state. As a re­sult, ice is 9% less com­pact than liq­uid wa­ter.

Japanese macaque in water [Deposit Photos]

Wa­ter is in­cred­i­bly mo­bile. It con­stant­ly moves across the en­tire Earth in a cy­cle of evap­o­ra­tion, con­den­sa­tion and pre­cip­i­ta­tion. Its mo­bil­i­ty also af­fects oth­er or­gan­isms in which hy­dro­gen and oxy­gen com­po­nents con­stant­ly unite and re­ar­range them­selves in bio­chem­i­cal pro­cess­es.

We not only con­sume wa­ter, but also pro­duce it. Ev­ery time when glu­cose mol­e­cules in the body break down, six wa­ter mol­e­cules form. This re­ac­tion takes place in the body of the av­er­age per­son 6 sep­til­lion (6 with 24 ze­roes) times a day. Nev­er­the­less, we can­not cov­er our need for wa­ter in this way.


A dis­in­te­grat­ing glacier

How much do we have?

Gen­er­al­ly, there is quite a lot of wa­ter in the uni­ver­sal, and this is quite log­i­cal. The three most wide­spread el­e­ments in the uni­verse are hy­dro­gen, he­li­um and oxy­gen. But as he­li­um is in­ert and does not en­ter into chem­i­cal re­ac­tions, a com­pound of the two oth­er el­e­ments, i.e. wa­ter, is en­coun­tered quite fre­quent­ly. At the same time, all the wa­ter on Earth would form a sphere with a di­am­e­ter of around 1400 km. This is al­most 10 times less than the di­am­e­ter of the Earth it­self. Of this vol­ume, only 3% is fresh wa­ter. So for each cup of sea wa­ter, there is just a lit­tle more than a tea­spoon of fresh wa­ter. 85% of fresh wa­ter on the plan­et is held in glaciers and po­lar ice. The growth of the pop­u­la­tion, pol­lu­tion of wa­ter bod­ies and a num­ber of oth­er fac­tors make it in­creas­ing­ly like­ly that in the 21st cen­tu­ry fresh wa­ter may be­come a deficit, and cost more than petrol.

For­tu­nate­ly, to­day we still have the op­por­tu­ni­ty to raise a glass of wa­ter to the most amaz­ing mol­e­cule.