Tag Archives: Antoine Lavoisier

Freezing fungal farts: what is hair ice and why does it form?

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Hair ice, in which ice crystals grow in thread-like structures, can be found at northerly latitudes in broadleaf forests [image source]

I’ve written about water before and in particular, if you’ve been paying very close attention, you might remember that November 12th marks the anniversary of the day, in 1783, that Antoine Lavoisier formally declared water to be a compound rather than an element.

Which means that November is always an excellent time to talk about water. But this time, I’m going to focus on its solid state: ice.

A few days ago I stumbled across some beautiful images of hair ice, which prompted me to make a #272sci Twitter post (keep an eye on that hashtag for similar small bits of interesting science). The story behind hair ice is a fascinating one, and not something I could truly cover in 272 characters – so here’s the slightly longer version…

This form of ice is found on dead wood, and it has a few other names, including ice wool or frost beard. Of course, ice naturally forms at 0 ℃ at standard atmospheric pressure, but the form we’re most familiar with looks, to the naked eye at least, rather more random. In fact, it was snowing here just yesterday, which means I have photos!

Ice crystals on a wall in Oxfordshire, UK, in November 2021

As you can (hopefully) see, there’s some regularity to the individual crystals, but they’re sort of growing all over the place. So, how do ice crystals form, and why?

We need to start with the structure of water. Now, you might imagine that a molecule with the formula H2O would have its atoms arranged in a straight line, like this: H–O–H. But it doesn’t, and the reason it doesn’t is that the oxygen atom in the middle has two pairs of electrons which aren’t involved in bonding – which chemists call ‘lone pairs‘.

Imagine, for a moment, that you have a bunch of balloons made up of two sausage-shaped balloons and two round ones, all attached at the neck. What shape would they make, as a whole? Probably, the two long balloons would form a sort of rough V, and the two round ones would stick out, opposite each other.

If you have some balloons to hand, give it a try. It turns out this is actually a pretty good model for water. We end up with a roughly tetrahedral shape, with oxygen in the middle, hydrogen atoms in two of the corners, and the lone pairs in the other two corners.

The H2O atoms in a water molecule adopt a sort of shallow V shape but, if you consider the lone pairs, the molecule actually forms a rough tetrahedron [image source]

This is important because those lone pairs don’t just sit around doing nothing. The element oxygen is very electronegative, which means it likes to attract bonded electrons. Hydrogen, by contrast, is more electropositive, which essentially means it doesn’t.

The result of this is that, although it is very definitely a covalently-bonded molecule (and not made up of ions), the oxygen atom in water has a partially negative charge, while the hydrogens have a partially-positive charge.

Since positive charges attract negative charges, and since molecules don’t exist in isolation. The result is that the hydrogen atoms in one water molecule are attracted to the oxygens in other water molecules. This is called hydrogen bonding.

If your head is spinning as you try to imagine this, take a look at the image below. White is hydrogen, red is oxygen, and the dashed lines represent the attractions between partially-positive hydrogens and partially-negative oxygens.

Do you see the shapes that form? Yes – hexagons!

When water molecules pack together they form hexagonal shapes [image source]

And how many sides does a snowflake have? Yes – six!

It’s not a coincidence: as the temperature drops, molecules that previously had freedom of movement gradually stop moving so much and pack into these hexagonal shapes. Then, water vapour in the air deposits onto this skeleton and, voilà, we end up with six-sided ice crystals.

Now, normally, this happens fairly randomly. Yes, all the snowflakes are hexagonal (and there are images of the different patterns that can form in this graphic from Compound Interest) but, as my photos of ice crystals suggest, they tend to stick out in all directions.

Hair ice is different. The ‘hairs’ appear at what are called wood rays, that is, lines perpendicular to the growth rings of the wood, and it turns out that if a piece of wood forms hair ice once, it will probably keep producing it – which makes things rather easier for the potential photographer!

Each of the hairs is about 0.02 mm thick and, assuming the temperature doesn’t rise above freezing, they can hang around for hours and even days.

Why does hair ice grow in single, curling strands, rather than forming this more typical ‘bushy’ structure?

Which leads to the question: why don’t more ice crystals grow on top of the threads and break up the hair-like structures? After all, if it’s cold enough for ice, it ought to be cold enough for, well, more ice – oughtn’t it?

A quick aside: you’ve probably heard of Alfred Wegener, discoverer of continental drift – an idea that ultimately led to modern tectonic plate theory. These days, those ideas are pretty universally accepted, but when Wegener first proposed continental drift in 1912, he faced a lot of opposition. There was more than one reason for this, but one major one was that Wegener was seen as an outsider to the field of geophysics. His background was in meteorology and polar research. In other words, he spent a lot of time in cold weather conditions.

Which brings me back to the main, ah, thread (sorry). Alfred Wegener described hair ice on wet dead wood in 1918, having observed it the year before, and suggested that mycelium, the thread-like part of a fungal colony, could be involved. He thought this because he could actually see mycelium on the branch surface, which was confirmed by his consultant, Arthur Meyer. Meyer, however, was unable to definitely identify the fungal species at the time.

Some years later, in 1975, scientists named Mühleisen and Lämmle actually managed to grow hair ice on rotten wood in a climate chamber and later still, in 2005, the physicist Gerhart Wagner again suggested that a fungus was involved, although he had no knowledge of Wegener’s observations when he first did so. He went on to carry out experiments with Christian Mätzler in which they were able to reliably grow hair ice on a balcony on nights with freezing conditions.

A photo of hair ice taken in British Columbia, Canada, by Tiarra Friskie

After lots of painstaking (and cold!) observation, they concluded two things: firstly, hair ice forms from water stored in the wood, not atmospheric water – which goes some way to explaining why the structures aren’t more random, as you’d expect if the ice were forming from water vapour in the air.

Secondly, the fungus, as a product of its metabolism, was generating gas pressure, and that was pushing water through the wood rays to the wood surface, where it was fanning out into fine, curling strands.

So, yes, in a way, hair ice is the product of freezing fungal farts. (Yes, yes, very tenuous, but I couldn’t resist ‘freezing fungal farts’, let me have this one.)

There’s a much more scientific explanation in this 2015 paper, the full text of which is freely available online (lots of great photos too!). The culprit turns out to be a fungus called Exidiopsis effusa. Inside the wood, attractions between the water molecules and the wood surface lower the melting point of water slightly, keeping it liquid. Products of wood decomposition left by the fungus also (probably) help to prevent ice forming inside the wood itself.

Once the outside temperature drops, though, the formation of ice crystals on the outer surface of the wood has the effect of drawing out more water, and the result is that the crystals grown in long, thread-like structures – although the fine details of how the fungus does what it does are still a bit of a mystery. Still, it’s nice to find a not-quite-answered science question, isn’t it?

More hair ice in the wild, by Tiarra Friskie

One final thing: just in case you were thinking, oh, come on, is that first picture really real? On the Chronicle Flask Facebook page, a user named Tiarra Friskie commented that they had pictures of this very phenomenon, taken in British Columbia, Canada, and kindly gave me permission to use them. So, here you are: a tiny bit meltier than the picture above, but nevertheless, two guaranteed genuine photographs of hair ice!

If you live somewhere in the vicinity of the latitudes between 45 and 55 °N (which includes most of the UK, by the way), keep an eye out for rotten wood in your local broadleaf forest – if the weather gets cold enough, you might just spot some hair ice yourself.

A little admin note: the chronicle flask blog is now (yikes) almost nine years and 150 posts old. Life is increasingly busy and so, after December 2021, I’m going to stop making monthly updates. But not to worry! You can still follow the Twitter hashtag #272sci for regular tiny pieces of science, and I’ll pop back every now and then. Oh, and please do consider supporting the Great Explanations book project here!

Plus, why not take a look at my fiction blog: the fiction phial? And you can also find me doing various flavours of editor-type-stuff at the horror podcast, PseudoPod.org – so head over there, too!

Content is © Kat Day 2021. You may share or link to anything here, but you must reference this site if you do. You can support my writing my buying a super-handy Pocket Chemist from Genius Lab Gear using the code FLASK15 at checkout (you’ll get a discount, too!) or by buying me a coffee – just hit this button:
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How many scientists does it take to discover five elements? More than you might think…

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My last post chronicled (see what I did there?) a meandering stroll through all 118 elements in the periodic table. As I read through all the pieces of that thread, I kept wanting to find out more about some of the stories. This is the international year of the periodic table, after all — what better time to go exploring?

But, here’s the thing: 118 is a lot. It took ages even just to collect all the (mostly less than) 280-character tweets together. Elemental stories span the whole of human existence and are endlessly fascinating, but telling all of them in any kind of detail would take whole book (not a small one, either) and would be a project years in the making. So, how about instead having a look at some notable landmarks? A sort of time-lapse version of elemental history and discovery, if you will…

Carbon

The word “carbon” comes from the Latin “carbo”, meaning coal and charcoal.

Let’s begin the story with carbon: fourth most abundant element in the universe and tenth most abundant in the Earth’s crust (give or take). When the Earth first formed, about 4.54 billion years ago, volcanic activity resulted in an atmosphere that was mostly carbon dioxide. The very earliest forms of life evolved to use carbon dioxide through photosynthesis. Carbon-based compounds make up the bulk of all life on this planet today, and carbon is the second most abundant element in the human body (after oxygen).

When we talk about discovering elements, our minds often leap to “who”. But, as we’ll see throughout this journey, that’s never an entirely straightforward question. The word “carbon” comes from the Latin carbo, meaning coal and charcoal. Humans have known about charcoal for many thousands of years — after all, if you can make a fire, it’s not long before you start to wonder if you can do something with this leftover black stuff. We’ll never know who first “discovered” carbon. But we can be sure of one thing: it definitely wasn’t an 18th century European scientist.

Diamond is a form of carbon used by humans for over 6000 years.

Then there are diamonds, although of course it took people a bit longer to understand how diamonds and other forms of carbon were connected. Human use of diamonds may go back further than we imagine, too. There’s evidence that the Chinese used diamonds to grind and polish ceremonia tools as long as 6,000 years ago.

Even the question of who first identified carbon as an element isn’t entirely straightforward. In 1722, René Antoine Ferchault de Réaumur demonstrated that iron was turned into steel by absorbing some substance. In 1772, Lavoisier showed for the first time that diamonds could burn (contrary to a key plot point in a 1998 episode of Columbo).

In 1779, Scheele demonstrated that graphite wasn’t lead, but rather was a form of charcoal that formed aerial acid (today known as carbonic acid) when it was burned and the products dissolved in water. In 1786 Claude Louis Berthollet, Gaspard Monge and C. A. Vandermonde again confirmed that graphite was mostly carbon, and in 1796, Smithson Tennant showed that burning diamond turned limewater milky — the established test for carbon dioxide gas — and argued that diamond and charcoal were  chemically identical.

Even that isn’t quite the end of the story: fullerenes were discovered 1985, and Harry Kroto, Robert Curl, and Richard Smalley were awarded a Nobel Prize for: “The discovery of carbon atoms bound in the form of a ball” in 1996.

Type “who discovered carbon” into a search engine and Lavoisier generally appears, but really? He was just one of many, most of whose names we’ll never know.

Zinc

Brass, an alloy of zinc, has been used for thousands of years.

Now for the other end of the alphabet: zinc. It’s another old one, although not quite as old as carbon. Zinc’s history is inextricably linked with copper, because zinc ores have been used to make brass alloys for thousands of years. Bowls made of alloyed tin, copper and zinc have been discovered which date back to at least 9th Century BCE, and many ornaments have been discovered which are around 2,500 years old.

It’s also been used in medicine for a very long time. Zinc carbonate pills, thought to have been used to treat eye conditions, have been found on a cargo ship wrecked off the Italian coast around 140 BCE, and zinc is mentioned in Indian and Greek medical texts as early as the 1st century CE. Alchemists burned zinc in air in 13th century India and collected the white, woolly tufts that formed. They called it philosopher’s wool, or nix alba (“white snow”). Today, we know the same thing as zinc oxide.

The name zinc, or something like it, was first documented by Paracelsus in the 16th century — who called it “zincum” or “zinken” in his book, Liber Mineralium II. The name might be derived from the German zinke, meaning “tooth-like” — because crystals of tin have a jagged, tooth-like appearance. But it could also suggest “tin-like”, since the German word zinn means tin. It might even be from the Persian word سنگ, “seng”, meaning stone.

These days, zinc is often used as a coating on other metals, to prevent corrosion.

P. M. de Respour formally reported that he had extracted metallic zinc from zinc oxide in 1668, although as I mentioned above, in truth it had been extracted centuries before then. In 1738, William Champion patented a process to extract zinc from calamine (a mixture of zinc oxide and iron oxide) in a vertical retort smelter, and Anton von Swab also distilled zinc from calamine in 1742.

Despite all that, credit for discovery of zinc usually goes to Andreas Marggraf, who’s generally considered the first to recognise zinc as a metal in its own right, in 1746.

Helium

Evidence of helium was first discovered during a solar eclipse.

Ironically for an element which is (controversially) used to fill balloons, helium’s discovery is easier to pin down. In fact, we can name a specific day: August 18, 1868. The astronomer Jules Janssen was studying the chromosphere of the sun during a total solar eclipse in Guntur, India, and found a bright, yellow line with a wavelength of 587.49 nm.

In case you thought this was going to be simple, though, he didn’t recognise the significance of the line immediately, thinking it was caused by sodium. But then, later the same year, Norman Lockyer also observed a yellow line in the solar spectrum — which he concluded was caused by an element in the Sun unknown on Earth. Lockyer and Edward Frankland named the element from the Greek word for the Sun, ἥλιος (helios).

Janssen and Lockyer may have identified helium, but they didn’t find it on Earth. That discovery was first made by Luigi Palmieri, analysing volcanic material from Mount Vesuvius in 1881. And it wasn’t until 1895 that William Ramsay first isolated helium by treating the mineral cleveite (formula UO2) with acid whilst looking for argon.

Mendeleev’s early versions of the periodic table, such as this one from 1871, did not include any of the noble gases (click for image source).

Interestingly, Mendeleev’s 1869 periodic table had no noble gases as there was very little evidence for them at the time. When Ramsay discovered argon, Mendeleev assumed it wasn’t an element because of its unreactivity, and it was several years before he was convinced that any of what we now call the noble gases should be included. As a result, helium didn’t appear in the periodic table until 1902.

Who shall we say discovered helium? The astronomers, who first identified it in our sun? Or the chemists, who managed to collect actual samples on Earth? Is an element truly “discovered” if you can’t prove you had actual atoms of it — even for a brief moment?

Francium

So far you may have noticed that all of these discoveries have been male dominated. This is almost certainly not because women were never involved in science, as there are plenty of records suggesting that women often worked in laboratories in various capacities — it’s just that their male counterparts usually reported the work. As a result the men got the fame, while the women’s stories were, a lot of the time, lost.

Marguerite Perey discovered francium (click for image source).

Of course, the name that jumps to mind at this point is Marie Curie, who famously discovered polonium and radium and had a third element, curium, named in honour of her and her husband’s work. But she’s famous enough. Let’s instead head over to the far left of the periodic table and have a look at francium.

Mendeleev predicted there ought to be an element here, following the trend of the alkali metals. He gave it the placeholder name of eka-caesium, but its existence wasn’t to be confirmed for some seventy years. A number of scientists claimed to have found it, but its discovery is formally recorded as having been made in January 1939 by Marguerite Perey. After all the previous failures, Perey was incredibly meticulous and thorough, carefully eliminating all possibility that the unknown element might be thorium, radium, lead, bismuth, or thallium.

Perey temporarily named the new alkali metal actinium-K (since it’s the result of alpha decay of 227Ac), and proposed the official name of catium (with the symbol Cm), since she believed it to be the most electropositive cation of the elements.

But the symbol Cm was assigned to curium, and Irène Joliot-Curie, one of Perey’s supervisors, argued against the name “catium”, feeling it suggested the element was something to do with cats. Perey then suggested francium, after her home country of France, and this was officially adopted in 1949.

A sample of uraninite containing perhaps 100,000 atoms of francium-223 (click for image source).

Francium was the last element to be discovered in nature. Trace amounts occur in uranium minerals, but it’s incredibly scarce. Its most stable isotope has a half life of just 22 minutes, and bulk francium has never been observed. Famously, there’s at most 30 g of francium in the Earth’s crust at any one time.

Of all the elements I’ve mentioned, this is perhaps the most clear-cut case. Perey deservedly takes the credit for discovering francium. But even then, she wouldn’t have been able to prove so conclusively that the element she found wasn’t something else had it not been for all the false starts that came before. And then there are all the other isotopes of francium, isolated by a myriad of scientists in the subsequent years…

Tennessine

All of which brings us to one of the last elements to be discovered: tennessine (which I jokingly suggested ought to be named octarine back in 2016). As I mentioned above, francium was the last element to be discovered in nature: tessessine doesn’t exist on Earth. It has only ever been created in a laboratory, by firing a calcium beam into a target made of berkelium (Bk) and smashing the two elements together in a process called nuclear fusion.

Element 117, tennessine, was named after Tennessee in the USA.

Like tennessine, berkelium isn’t available on Earth and had to be made in a nuclear reactor at Oak Ridge National Laboratory (ORNL) in Tennessee — the reason for the new element’s name. One of the scientists involved, Clarice E. Phelps, is believed to be the first African American to discover a chemical element in recent history, having worked on the purification of the 249Bk before it was shipped to Russia and used to help discover element 117.

Tennessine’s discovery was officially announced in Dubna in 2010 — the result of a Russian-American collaboration — and the name tennessine was officially adopted in November 2016.

Who discovered it? Well, the lead name on the paper published in Physical Review Letters is Yuri Oganessian (for whom element 118 was named), but have a look at that paper and you’ll see there’s a list of over 30 names, and that doesn’t even include all the other people who worked in the laboratories, making contributions as part of their daily work.

From five to many…

There’s a story behind every element, and it’s almost always one with a varied cast of characters.

As I said at the start, when we talk about discovering elements, our minds often leap to “who” — but they probably shouldn’t. Scientists really can’t work entirely alone: collaboration and communication are vital aspects of science, because without them everyone would have to start from scratch all the time, and humans would never have got beyond “fire, hot”. As Isaac Newton famously said in a letter in 1675: “If I have seen further it is by standing on the shoulders of giants.”

There’s a story behind every element, and it’s almost always one with a varied cast of characters.

This post was written by with the help of Kit Chapman (so, yes: it’s by Kit and Kat!). Kit’s new book, ‘Superheavy: Making and Breaking the Periodic Table‘, will be published by Bloomsbury Sigma on 13th June.

Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. Content is © Kat Day 2019. You may share or link to anything here, but you must reference this site if you do. If you enjoy reading my blog, please consider buying me a coffee through Ko-fi using the button below.
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2019: The Year of the Periodic Table

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The Periodic Table

2019 is the International Year of the Periodic Table

In case you missed it, 2019 is officially the International Year of the Periodic Table, marking 150 years since Dmitri Mendeleev discovered the “Periodic System”.

Well, this is a chemistry blog, so it would be pretty remiss not to say something about that, wouldn’t it? So, here’s a really quick summary of how we got to the periodic table we all know and love…

Around 400 BCE, the Greek philosopher Democritus (along with a couple of others) suggested that everything was composed of indivisible particles, which he called “atoms” (from the Greek atomos). The term ‘elements’ (stoicheia) was first used around 360 BCE by Plato, although at that time he believed matter to be made up of tiny units of fire, air, water and earth.

Skipping over a few centuries of pursuing what was, we know now, a bit of a dead-end in terms of the whole earth, air, fire and water thing, in 1661, Robert Boyle was probably the first to state that elements were the building blocks of matter and were irreducible but, and this was the crucial bit, that we didn’t know what all the elements were, or even how many there might be.

Antoine Lavoisier wrote one of the first lists of chemical elements.

Antoine Lavoisier (yep, him again) wrote one of the first lists of chemical elements, in his 1789 Elements of Chemistry. He listed 33 of them, including some that turned out not to be elements, such as light.

Things moved on pretty quickly after that. Just thirty years later, Jöns Jakob Berzelius had worked out the atomic weights for 45 of the 49 elements that were known at that point.

So it was that by the 1810s, chemists knew of 50 or so chemical elements, and had atomic weights for most of them. It was becoming clear that more elements were going to turn up, and the big question became: how do we organise this ever-increasing list? It was a tricky problem. Imagine trying to put together a jigsaw puzzle where two-thirds of the pieces are missing, there’s no picture on the box, and a few pieces have been tossed in from other puzzles for good measure.

Enter Johann Döbereiner, who in 1817 noticed that there were patterns in certain groups of elements, which he called triads. For example, he spotted that lithium, sodium and potassium behaved in similar ways, and realised that if you worked out the average atomic mass of lithium and potassium, you got a value that was close to that of sodium’s. At the time he could only find a few triads like this, but it was enough to suggest that there must be some sort of structure underlying the list of elements.

In 1826 Jean-Baptiste Dumas (why do all these chemists have first names starting with J?) perfected a method for measuring vapour densities, and worked out new atomic mass values for 30 elements. He also set the value for hydrogen at 1, in other words, placing hydrogen as the “first” element.

Newland’s table of the elements had “periods” going down and “groups” going across, but otherwise looks quite familiar.

Next up was John Newlands (another J!), who published his “Law of Octaves” in 1865. Arranging the elements in order of atomic mass, he noticed that properties seemed to be repeating in groups of eight. His rows and columns were reversed compared to what we use today — he had groups going across, and periods going down — but apart from that the arrangement he ended up with is decidedly familiar. Other chemists, though, didn’t appreciate the musical reference, and didn’t take Newlands very seriously.

Which brings us, finally, to Dmitri Mendeleev (various other spellings of his name exist, including Dmitry Mendeleyev, but Dmitri Mendeleev seems to be the most accepted one). His early life history is a movie-worthy story (I won’t go into that else we’ll be here all day, but check it out, it’s really quite amazing). When he was just 35 he made a formal presentation to the Russian Chemical Society, titled The Dependence between the Properties of the Atomic Weights of the Elements, which made a number of important points. He noted, as Newlands had already suggested, that there were repeating patterns in the elements, or periodicity, and that there did indeed seem to be connections between sequences of atomic weights and chemical properties.

Dmitri Mendeleev suggested there were many elements yet to be discovered.

Most famously, Mendeleev suggested that there were many elements yet to be discovered, and he even went so far as to predict the properties of some of them. For example, he said there would be an element with similar properties to silicon with an atomic weight of 70, which he called ekasilicon. The element was duly discovered, in 1886 by Clemens Winkler, and named germanium, in honor of Germany: Winkler’s homeland. Germanium turns out to have an atomic mass of 72.6.

Mendeleev also predicted the existence of gallium, which he named ekaaluminium, and predicted, amongst other things, that it would have an atomic weight of 68 and a density of 5.9 g/cm3. When the element was duly discovered by the French chemist Paul Emile Lecoq de Boisbaudran, he first determined its density to be 4.7 g/cm3. Mendeleev was so sure of his prediction that he wrote to Lecoq and told him to check again. It turned out that Mendeleev was right: gallium’s density is actually 5.9 g/cm3 (and its atomic weight is 69.7).

Despite constructing the one thing that every chemist over the last 150 years has spent years of their life poring over, Mendeleev was never awarded the Nobel Prize for Chemistry. He was nominated in 1906, but the story goes that Svante Arrhenius — who had a lot of influence in the Royal Swedish Academy of Sciences — held a grudge against Mendeleev because he’d been critical of Arrhenius’s dissociation theory, and argued that the periodic system had been around for far too long by 1906 to be recognised for the prize. Instead, the Academy awarded the Nobel to Henri Moissan, for his work on isolating fluorine from its compounds (no doubt impressive, not to mention dangerous, chemistry).

Henry Moseley

Henry Moseley proposed that atomic number was equal to the number of protons in the nucleus of an atom.

Mendeleev died in 1907 at the age of 72, just before the discovery of the proton and Henry Moseley’s work, in 1913, which proposed that the atomic numbers of elements should be equal to the number of positive charges (protons) they contained in their nuclei. This discovery would have pleased Mendeleev, who had already suggested, based on their properties, that some elements shouldn’t be placed in the periodic table strictly in order of atomic weight.

After which, of course, came the discovery of the neutron — which would finally clear up the whole atomic mass/atomic number thing — atomic orbital theory, and the discovery of super-heavy elements. The most recent additions to the modern periodic table were the official names, in 2016, of the final four elements of period 7: nihonium (113), moscovium (115), tennessine (117) and oganesson (118).

Which brings us up to date. For now…

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What is Water? The Element that Became a Compound

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November 2018 marks the 235th anniversary of the day when Antoine Lavoisier proved water to be a compound, rather than an element.

I’m a few days late at the time of writing, but November 12th 2018 was the 235th anniversary of an important discovery. It was the day, in 1783, that Antoine Lavoisier formally declared water to be a compound, not an element.

235 years seems like an awfully long time, probably so long ago that no one knew anything very much. Practically still eye of newt, tongue of bat and leeches for everyone, right? Well, not quite. In fact, there was some nifty science and engineering going on at the time. It was the year that Jean-François Pilâtre de Rozier and François Laurent made the first untethered hot air balloon flight, for example. And chemistry was moving on swiftly: lots of elements had been isolated, including oxygen (1771, by Carl Wilhelm Scheele) and hydrogen (officially by Henry Cavendish in 1766, although others had observed it before he did).

Cavendish had reported that hydrogen produced water when it reacted with oxygen (known then as inflammable air and dephlogisticated air, respectively), and others had carried out similar experiments. However, at the time most chemists favoured phlogiston theory (hence the names) and tried to interpret and explain their results accordingly. Phlogiston theory was the idea that anything which burned contained a fire-like element called phlogiston, which was then “lost” when the substance burned and became “dephlogisticated”.

Cavendish, in particular, explained the fact that inflammable air (hydrogen) left droplets of “dew” behind when it burned in “common air” (the stuff in the room) in terms of phlogiston, by suggesting that water was present in each of the two airs before ignition.

Antoine-Laurent Lavoisier proved that water was a compound. (Line engraving by Louis Jean Desire Delaistre, after a design by Julien Leopold Boilly.)

Lavoisier was very much against phlogiston theory. He carried out experiments in closed vessels with enormous precision, going to great lengths to prove that many substances actually became heavier when they burned and not, as phlogiston theory would have it, lighter. In fact, it’s Lavoisier we have to thank for the names “hydrogen” and “oxygen”. Hydrogen is Greek for “water-former”, whilst oxygen means “acid former”.

When, in June 1783, Lavoisier found out about Cavendish’s experiment he immediately reacted oxygen with hydrogen to produce “water in a very pure state” and prove that the mass of the water which formed was equal to the combined masses of the hydrogen and oxygen he started with.

He then went on to decompose water into oxygen and hydrogen by heating a mixture of water and iron filings. The oxygen that formed combined with the iron to form iron oxide, and he collected the hydrogen gas over mercury. Thanks to his careful measurements, Lavoisier was able to demonstrate that the increased mass of the iron filings plus the mass of the collected gas was, again, equal to the mass of the water he had started with.

Water is a compound of hydrogen and oxygen, with the formula H2O.

There were still arguments, of course (there always are), but phlogiston theory was essentially doomed. Water was a compound, made of two elements, and the process of combustion was nothing more mysterious than elements combining in different ways.

As an aside, Scottish chemist Elizabeth Fulhame deserves a mention at this point. Just a few years after Lavoisier she went on to demonstrate through experiment that many oxidation reactions occur only in the presence of water, but the water is regenerated at the end of the reaction. She is credited today as the chemist who invented the concept of catalysis. (Which is a pretty important concept in chemistry, and yet her name never seems to come up…)

Anyway, proving water’s composition becomes a lot simpler when you have a ready supply of electricity. The first scientist to formally demonstrate this was William Nicholson, in 1800. He discovered that when leads from a battery are placed in water, the water breaks up to form hydrogen and oxygen bubbles, which can be collected separately at the submerged ends of the wires. This is the process we now know as electrolysis.

You can easily carry out the electrolysis of water at home.

In fact, this is a really easy (and safe, I promise!) experiment to do yourself, at home. I did it myself, using an empty TicTac box, two drawing pins, a 9V battery and a bit of baking soda (sodium hydrogencarbonate) dissolved in water – you need this because water on its own is a poor conductor.

The drawing pins are pushed through the bottom of the plastic box, the box is filled with the solution, and then it’s balanced on the terminals of the battery. I’ve used some small test tubes here to collect the gases, but you’ll be able to see the bubbles without them.

Bubbles start to appear immediately. I left mine for about an hour and a half, at which point the test tube on the negative terminal (the cathode) was completely full of gas, which produced a very satisfying squeaky pop when I placed it over a flame.

The positive electrode (the anode) ended up completely covered in what I’m pretty sure is a precipitate of iron hydroxide (the drawing pins presumably being plated steel), which meant that very little oxygen was produced after the first couple of minutes. This is why in proper electrolysis experiments inert graphite or, even better, platinum, electrodes are used. If you do that, you’ll get a 1:2 ratio by volume of oxygen to hydrogen, thus proving water’s formula (H2O) as well.

So there we have it: water is a compound, and not an element. And if you’d like to amuse everyone around the Christmas dinner table, you can prove it with a 9V battery and some drawing pins. Just don’t nick the battery out of your little brother’s favourite toy, okay? (Or, if you do, don’t tell him it was my idea.)

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Why is chemistry the forgotten science?

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I recently had the privilege of talking to radio DJ and author Simon Mayo and he asked me what I thought of his book, Itch.  I said I loved it, and I really do.  (I have yet to read the sequel, Itch Rocks – released at the end of February – but it’s definitely on my list.)  I like Itch for many reasons.  I liked it because the lead character is a teenage boy who’s interested in science and actually finds arty subjects rather difficult, and yet is not a nerdy stereotype.  I like it because there was lots of action and an interesting story, coupled with just the right amount of research.  I liked it because the main female character is strong-willed, principled and absolutely doesn’t get involved in any sort of love triangle (this is not, to paraphrase my favourite film, ‘a kissing book’).  And most of all, I like it because it’s science fiction about chemistry.chemistry

As a chemist, it’s long seemed to me that, when it comes to the media and fiction, it’s the forgotten science. I can think of any number of famous science fiction works that hinge around physics and astronomy.  I can think of things based on biology.  I can even recall one or two that have both, for example Christian Cantrell’s Containment, a novel about a brilliant young scientist living on Venus and working on artificial photosynthesis.  But when it comes to chemistry I’m struggling.  Poisoning turns up in quite a few murder mysteries of course, as does forensics.  I suppose you could argue that some of the medical thrillers with plots that hinge around drugs might count.   Nanotechnology, as in Prey by Michael Crichton, is often thought of as a chemical field in the real world (TM), but thrillers on the subject tend to be less about matter on the atomic scale and more about improbably aggressive tiny robots.

It’s not just fiction.  In recent years there has been a noticeable increase in the amount of science programming, particularly on the BBC.  This is fabulous, but the large majority has been focused on physics and biology.  Radio 4’s The Infinite Monkey Cage often takes great glee in ignoring, and even ridiculing, chemical disciplines (I still listen to it mind you, in the manner of someone poking at a sore tooth).  The current run of BBC’s Horizon has exactly one episode (The Truth about Taste) that might be considered to have a chemistry focus.  At the end of last year Dara O Briain’s Science Club managed a whole series of six episodes without a single one on a chemical topic.  And so on and so on.  At least the most recent Royal Institution Christmas Lectures redressed the balance a bit, even if they were tucked away on BBC Four.  And as I posted recently, the quiz show Pointless seems to be quite fond of chemistry as a topic, so that’s something.

But why the general lack of chemistry?  Especially when you consider that the A-level is not only desirable but an essential requirement for so many degrees, including medicine, veterinary science, dentistry and pharmacy.  Whereas physics and, perhaps more surprisingly, biology aren’t. Since it’s so important you’d imagine there would be a bit more enthusiasm for the subject.

Is it linked to the background of the presenters?  Dara O Briain, in a previous life, studied mathematics and theoretical physics.  Professor Brian Cox, presenter of the Infinite Monkey Cage, is of course a physicist.  The only regular presenter I can think of with anything resembling a chemistry degree (actually biochemistry) is Liz Bonnin of Bang Goes the Theory.  But surely it isn’t impossible to find a chemist capable of presenting?  Peter Wothers did a cracking job with the Royal Institution lectures for starters.  And surely, surely, there’s room for the fabulously eccentric-looking Martyn Poliakoff somewhere?  (Please go and look at The Periodic Table of Videos if you have five minutes – it’s brilliant.)

But I’m not sure that’s the problem.  I imagine presenters largely talk about what they’re told to talk about.  No, I fear it might be simply the fact that chemistry is a bit, well, hard.

Early in my teaching career an exasperated A-level student complained, “miss, I thought chemistry was all setting fire to things and explosions and stuff, but it’s mostly just numbers and symbols”.  I’m afraid there’s some truth to this, particularly by the time we get to A-level chemistry, although I do like to set fire to things wherever possible (in a controlled manner of course – I’m not an arsonist, I swear).

I often joke with students that chemists use equations because we’re lazy.  For example, take this very simple experiment that you probably do every day if you have a gas cooker – it’s what happens when you set fire to methane:

CH4 + 2O2 –> CO2 + 2H2O

Now let’s write that in words: One molecule of methane, which contains one carbon atom bonded to four hydrogen atoms, reacts with exactly two molecules of diatomic oxygen irreversibly to produce exactly one molecule of carbon dioxide, which contains one atom of carbon bonded to two oxygen atoms, and two molecules of water, which contains two atoms of hydrogen bonded to an oxygen atom. 

Phew.  You can see why chemists prefer the equation.  Imagine if we had to write something like that every time we wanted to describe a reaction?  We’d never get anywhere.  Plus, once you understand them, the equations allow you to see similarities between different reactions that could be easily missed otherwise.  The symbols are essential.  But they’re also a bit, well, impenetrable.  A TV show with lots of chemical symbols would be as impossible to understand as one presented in French for many, and rather more difficult to subtitle.

So yes, it can look a bit scary.  But it’s not impossible.  After all you need advanced mathematics to understand physics in depth, but plenty of physics programmes explain their subject matter without even hinting at the dreaded doublet of differentiation and integration.  A good chemist can make the subject accessible with a bit of creativity.

It’s not as if there’s not lots of interesting material (pun entirely intended).  Chemistry is the science behind explosives, cooking, medicines, bubbles, pigments and poisons.  It has a fascinating history, populated with characters such as Fritz Haber, the father of chemical warfare who also solved the problem of global food security, Glenn Seaborg who discovered ten (ten!) of those elements that loiter at the bottom of the periodic table, Henry Cavendish – discoverer of hydrogen and famously so shy he was unable to talk to women, Antoine Lavoisier, tax collector, traitor and the person who named both oxygen and hydrogen and let’s not forget Carl Wilhelm Scheele, discoverer of some of the most dangerous substances known to man.  There are endless stories that could be told, from the legal case of the Carbolic Smoke Ball to Kekule’s dreams of snakes eating their own tails, to bizarre medical practices such as antimony pills and the mystery of the Bradford Sweets poisoning.

If Simon Mayo can write a series of highly successful novels featuring chemistry aimed at young adults, it must surely be possible to make a few more shows on the topic.  So writers, editors and producters I beseech you not to be scared of chemistry.  Find yourself someone with a bit of knowledge in the area and get on with it.  For whatever chemistry is, it’s far from boring.

Do you know of any chemistry science fiction I’ve missed?  Have you got any favourite chemical stories that you think should be on telly?  Please tell me about them!