It’s a mystery: a compound consists of only two chemical elements, one of which is the simplest element in the known universe. A pair of hydrogen atoms, held tightly to a single oxygen atom, creates a minimalist arrangement that can be regarded as versatile and of great importance.
Illustration by Traci Daberko for USC Dornsife Magazine.
The value of water as a resource is often understood. Without a steady supply, civilization as we know it would not exist.
But as a substance – as a molecule – water tends to stay away from most people’s sense of surprise, which is too bad because it’s quite noticeable.
Shaping and Appearance
The basic molecular formula of water, H₂O, suggests a simple structure of three atoms in a straight line. But the physical properties of the three atoms force a different arrangement – a “V” shape with oxygen at the point. This nonlinear shape turns water into a remarkable substance with amazing capabilities.
The “V” shape forms due to the arrangement of electrons in the molecule, causing a charge imbalance, with the oxygen point of the “V” being slightly more damaging than the opposite end near the hydrogen atoms. . This slight separation means that the water molecules are polar – one anode and one cathode.
The polarization of the charge is at the root of the attractive properties of water. The slightly negative end of one water molecule attracts the slightly positive end of another water molecule and vice versa in what scientists call a hydrogen bond.
Hydrogen bonds between water molecules are very strong, causing them to tend to stick together, a behavior most commonly expressed as surface tension. For example, water in a rim-filled vessel appears to bulge out of the vessel in a convex shape when viewed from the side due to surface tension. And some organisms, such as water pipes, can take advantage of surface tension to skim the surface of a pond.
Hydrogen bonds also facilitate water binding to foreign substances. This sticky quality allows plants to draw water from the ground, through the roots, and up to the tops of the leaves, despite the pull of gravity.
The polar nature of water and its resulting shape make it lighter in solid than liquid form. That’s because the V molecules form a breathable crystalline structure when they freeze, making ice less dense than its liquid form. So ice floats on rivers and lakes, forming a shield against the cold air above and keeping the water below from freezing, allowing fish and other aquatic life to survive in colder climates.
Hydrogen bonding of water also leads to another important property – a higher-than-expected boiling point, explained Jessica Parr, chemistry professor (teaching). Parr earned his PhD in chemistry from USC Dornsife in 2007 and has been teaching general chemistry to undergraduates ever since. Her dissertation research focused on understanding how hydrogen bonds react when exposed to intense light.
“If water were not capable of forming such strong hydrogen bonds, it would boil at minus 200 degrees Celsius,” explains Parr. freeze point 0 degrees Celsius. That means it would exist on Earth on a large scale as a gas, making life as we know it impossible. Instead, our planet is broken up by water, a total of about 366 million billion gallons.
A universal solvent
The polar nature of water also makes it a special solvent, capable of dissolving various substances.
“We call it the ‘universal solvent’ because it can dissolve, not everything, but a lot of things,” says Parr. they interact and how they work together, but water will interact with anything.”
For example, its negative and positive centers attract and easily separate charged ions, forming salts such as sodium chloride, commonly used in cooking. The positively charged sodium and negatively charged chloride atoms find a comfortable home drifting among the polar molecules of water.
But water can also dissolve non-ionic substances, such as sugar. However, instead of splitting the individual atoms of a sugar molecule, the water molecules work their way between each sugar molecule, finding the lightly charged parts to bond with the hydrogen. This loosens the bonds between the sugar molecules, pulling them apart and eventually becoming a solution.
“As long as there is one atom that makes the other want to interact with water, then water will do it,” says Parr.
It gets weird
Water doesn’t always work as expected. Although it usually changes from a solid (rock) to a liquid to a gas (vapor or water vapor) and vice versa as its temperature rises and falls, it can go directly from ice to vapor under extreme conditions. fit.
Parr explains: “If you’ve ever noticed that your ice cubes get smaller over time as they sublimate in your freezer – the ice goes straight to gas. This sublimation is due to the low humidity inside the freezer, which allows a few water molecules to escape from the ice into the air without first melting.
In the reverse process, called deposition, gaseous water suddenly freezes without ever becoming a liquid. This is how snow forms. And when conditions are right, snow can skip the melting phase and sublimate back into the atmosphere, a conundrum for drought-stricken areas like California, which rely on melting snow and ice as a source. country.
But water can be even weirder.
“Ice comes in many different crystalline forms, but it can also exist in the same form as glass – an amorphous solid that sits somewhere between a liquid and a solid and can still flow,” Parr said. When water molecules come together at shallow temperatures and pressures – think outer space – the result is that ice can also behave like glass, says Parr. Scientists suspect this may be one of the most common forms of water in the universe.
Mysteries and miracles continue
Despite its ubiquity in space and on Earth, and man’s longstanding familiarity with it, water continues to surprise.
Scientists recently discovered a form known as “superrionic ice”. Existing at extremely high pressures, such as in the cores of planets, it appears to play a role in maintaining Earth’s magnetic field.
And although water in its pure form is not a conductor, it behaves unexpectedly when exposed to an electric field. USC Dornsife’s Alexander Benderskiiassociate professor of chemistry, and Stephen Cronin of the USC Viterbi School of Engineering recently discovered that water molecules near the electrode line up differently than farther away.
“We were able to see how the molecules interact with the electric field in a way that nobody could understand before,” says Benderskii. The discovery could change the way chemists control reactions, including processes for making drugs and purifying drinking water.
As researchers continue to explore this unexpected, versatile substance, which has the potential to reveal more exotic properties, water may just be the most complex simple molecule in the universe.
Source: USC
