Molecule of the Month: 1st Anniversary
It’s time for a party! What are we celebrating? Not that we need an excuse to have a party, but there is actually something we can celebrate. This month marks one whole year since the very first molecule of the month, and whether you describe this as a birthday or our one year anniversary, either way we are having a chemistry party! What molecules do we need and what is the chemistry that makes a party awesome?
Party – but what about parts A-D?
We have explored a diverse range of molecules during the last 12 months. We saw the molecule vital for our eyesight and the molecule essential for keeping us safe from the sun’s harmful rays.
Then we delved into the molecules that keep us breathing free and keep us free from allergies. Away from health and our bodies, we have looked into the molecules involved in our everyday lives: the outdated, poisonous additive added to petrol, the explosive molecule used in gunpowder and fireworks, and the rapidly growing polymer that helps us to stick things together.
All of this definitely sounds like a reason to celebrate, and so you are all invited to a socially-distant party. But what will we need for our party? And more importantly, what molecules will be involved in our chemistry party, or indeed any party?
Up, up and anyway…
One of the main ways of identifying a party or celebration is chemistry textbooks…
It’s balloons. Red or blue, big or small, circular or elliptical, children’s party or elderly relative’s birthday, balloons are an ever-present sign of a party.
Aside from a party must-have, balloons are fascinating play-things. Many of us will have experimented, and even learnt, about static electricity by rubbing a balloon on our heads or jumpers and “sticking” it to the wall.
However, our interest is not what you can do with the surface of balloons, but rather what is inside the balloon, or any type of floating inflatable. If you’ve ever let go of a balloon and watched it helplessly float away up into the sky, then you are seeing first-hand the result of helium.
Helium – the first guest at our chemistry party
As far as elements go, helium is the lightest, second only to hydrogen. It is also the second most abundant element in the Universe, produced from the fusion of hydrogen that powers nearly every star during its lifetime.
Despite this, there is a rather small amount of helium on Earth. One problem is that helium is less dense (basically lighter) than air. This means that unless there is something to hold it back, helium will rise. And rise. And carry on rising up, before eventually disappearing off into space. This will be no surprise to those who have accidentally let go of a helium balloon and watched it soar away into the sky. Helium is located on the Periodic Table in the same group as neon, argon and krypton – otherwise known as the Noble Gases. These gases are well known for being very unreactive and not forming molecules with any other element, including itself.
Whilst helium’s chemical reactions are very dull and boring, its physical properties are very cool indeed. Talking of cool, the coldest temperature that can exist is known as absolute zero, -273.15°C. At this temperature and normal pressure, nearly every element exists as a solid… except helium. To obtain solid helium you have to lower the temperature to -272°C.. Then you also have to apply 2 500 000 Pa (mega pascals) of pressure!
Apart from filling up your balloon, helium is used to help keep things cool… very cool. Liquid helium is used to cool metals to make them superconductive and create superconductive magnets often used in MRI. The Large Hadron Collider at CERN uses liquid helium to help keep the temperatures close to -271°C. Helium is also used in combination with nitrogen and oxygen to create a special mixture of air called Trimix used for deep-sea divers.
A bittersweet remedy
Our party now has all the decorations we need and is looking magnificent. The next step is to get some drink in. Of course there will be carbonated fizzy drinks, fermented grapes in the form of wine for the adults and course some good old fashioned H2O. One increasingly popular alcoholic beverage is gin and tonic, often known as a G&T. In recent years much attention has been given to making lots of different types of gin. But what about the tonic? If you’ve ever tried it you’ll have noticed it has a bitter taste. This is because it contains quinine.
Quinine – the second guest at our chemistry party
The structure as quinine, as shown below, is complicated and contains two hexagonal rings next to each other, as well as a complicated looking arrangement of atoms at the other end of the molecule. Quinine is a naturally occurring chemical found in the bark of a tree called the cinchona tree. The structure of quinine gives rise to some very cool light effects. When placed in ultraviolet light, tonic water will give off an eerie light blue glow due to the quinine it contains. This is because the molecule can absorb ultraviolet light (which humans are unable to see), but emits light (fluoresces) that our eyes are able to see. This has been wonderfully highlighted by our friend Dr Sam Rowe: https://twitter.com/samfrowe/status/1271477923447541761
Aside from tonic water, quinine plays a vital role in human health, and indeed one of the most famous and important uses of this molecule is as a medicine to treat malaria. In fact, the use of the cinchona bark as a medicine had been used by the people’s of Peru and nearby countries for hundreds of years. Despite its medical benefits, quinine can also have serious side-effects, and so is really only used as an anti-malarial drug.
You’ve met your match
Of course no party is complete without cake! For many celebrations the cake is the focal point. When it is time to light the candles, everyone gathers around, sings a rendition of whatever song they fancy, and then eats lots and lots of cake. Let’s have a look at lighting the candles. In order to do this we need fire! The quickest and easiest way to obtain a small flame is to use matches. In some ways, matches can almost seem magical. A quick swish of the hand and this small wooden stick is suddenly ablaze with fire. But there is nothing mystical about matches; all we require is a little bit of chemistry in the form of phosphorous, and a small amount of frictional heat.
The ability to produce small flames quickly and wherever you went was very desirable. The history of matches is fascinating, however, we are going to skip ahead to the 1830s. At this moment in time, the heads of matches contained the element phosphorus, or to be more specific, white phosphorus.
White Phosphorus.. the most dangerous guest at our chemistry party!
In this form white phosphorus has a “pyramid”-like shape and is also highly flammable. This sounds like the ideal substance for a match . Unfortunately, white phosphorus is also rather pyrophoric, a fancy name to describe something that is self-igniting. In other words, white phosphorous can easily set alight all by itself. Something as simple of air is enough to set these matches alight. Not ideal for something you want to carry around with you or leave in a drawer somewhere.
In addition, white phosphorus is also extremely poisonous, and many people working in match factories suffered serious health effects and even death from working with it.
To solution to these problems was to switch to a substance called phosphorus sesquisulfide, (P4S3) a compound of phosphorus and sulfur with a very odd looking structure. This compound is not poisonous and also prevents the match heads from exploding.
P4S3 is the main form of phosphorus in strike anywhere matches. As the name suggests, these matches can be struck on any rough surface in order to ignite them. When struck, the phosphorous sesquisulfide is converted into a small amount of white phosphorus that then ignites. The ease with which this new phosphorus compound could be converted into white phosphorus could still be problematic, which eventually lead to the invention of the safety match.
Most matches used today in Europe are safety matches. These types of matches have two main differences to the strike anywhere matches. The first difference is the type of phosphorus used – red phosophorus. Another form of this element, but one that is much more stable. The other difference was the idea of putting the phosphorus on the side of the match box. You may have noticed that match boxes contain a rough side against which you strike the match. The match head itself, however, contains potassium chlorate. This time when struck, some of the red phosphorus is converted into white phosphorus. The friction also causes the combination of white phosphorus and potassium chlorate to ignite, giving us the vital flame needed to light the cakes on our candles.
Did you hear about the cleaning insect? It was a surfact-ant.
Sadly, the party has come to an end, the balloons are floating away, the cake has been eaten and the drink is all gone, resulting in everyone either being very hyper, or very inebriated. However, one task remains, the one everyone hates, but the one that has to be done – cleaning up!
Cleaning up our chemistry party
The post-party clean up will most likely involve a large bowl of hot soapy water. If you’re lucky you might have a large shiny dishwasher. In both cases, washing-up liquid is required to ensure those plates, dishes, glasses and cutlery are thoroughly clean. One of the main components of washing-up liquid is a class of molecules known as detergents.
There are various types of detergents, but they all have the same general structure. One part of the molecule (the head group) is water-loving and highly attracted towards it. We can say this part is hydrophilic. The other of the molecule (the tail group) is often a very long chain of hydrogen and carbon atoms. This end is “repelled” by water, but is attracted towards oil and grease. We can say this part is hydrophobic.
This combination of hydrophobic and hydrophilic parts makes these molecules ideal in washing-up detergent. The water-loving end helps the molecule to dissolve in the water. The water-hating end will seek out and be attracted to oil and greasy stains. When it finds an oily and greasy stain, the hydrophobic part of the molecule is attracted towards it, whilst the hydrophilic part wants to remain in the water.
The attraction of the head group to the water pulls the rest of the molecule, including the hydrophobic tail group. This helps to remove oil and grease off the surface of the plate, tray or even clothing and into the water. Once loose, the oil and grease is trapped inside a small circular cell made by the detergent molecules, and is then rinsed away. Even if it doesn’t completely remove the grease and oil, the detergent can help loosen it enough that some little scrubbing with a brush or sponge can easily remove it.
One common family of molecules used in detergent are the linear alkylbenzene sulfonates. These are anionic surfactants consisting of a negatively charged head group of sulfur and oxygen attached to a benzene ring, which is then attached to a long carbon chain.
So that is that. The party has been, come and gone. The helium filled balloons have been freed and are floating far away. Empty bottles of quinine containing tonic water have all been recycled. The matches are all out and the cake all eaten. Luckily for us, the alkylbenzene sulfonate detergents have made the washing up easy! Overall the party has been a massive success.
What next? Well there are still many, many, many molecules to explore and tales to tell. Hopefully we will see you again for the second year of molecule of the month and then our next anniversary! By then we should have more molecules and more chemistry to make the party even better.