Remarkable, reticent ruthenium

Ruthenium is rare transition metal belonging to the platinum group of elements

What shall I write about this week, I wonder… how about, apropos of nothing, the element ruthenium? It is the International Year of the Periodic Table after all; there have to be some element-themed posts, right?

Ruthenium has the atomic number 44 (good number, that) and the symbol Ru. It was officially discovered by Karl Ernst Klaus in 1844 (there it is again) at Kazan State University in Russia.

You might remember from school (or possibly from your jewellery) that platinum is really unreactive. What has this got to do with ruthenium? Well, unreactive metals can be found in nature as actual metal, rather than combined with other elements in ores. But it turns out that early “platinum metal” — used by pre-Columbian Americans — wasn’t pure, but was in fact an alloy of platinum with other metals.

Gottfried Osann discovered ruthenium before Klaus, but gave up his claim.

In 1827 Jöns Berzelius and Gottfried Osann dissolved crude platinum from the Ural Mountains in aqua regia: a 1:3 mixture of nitric acid and hydrochloric acid (we’ve met aqua regia before, in a famous story about Nobel Prize medals). Osann was certain that he’d isolated three new metals, which he named pluranium, ruthenium, and polinium, but Berzelius disagreed, and this caused a long-running dispute between the two scientists.

Osann eventually gave up the argument — which was a shame, because he was right. In 1844 Karl Ernst Klaus analysed the compounds prepared by Osann and showed that they did, in fact, contain ruthenium.

Klaus had been studying the insoluble residues left over after platinum extraction from Ural placer deposits. Like many chemists at the time, he tasted and smelled the substances he prepared, and he reported that the ammines of ruthenium had a more caustic taste than alkalis, while the taste of osmium tetroxide was “acute pepper-like” (do not try this at home).

He communicated his discoveries to the Academy of Sciences at St. Petersburg and to Academician G. I. Gess, who reported them on September 13th and October 25th, 1844. Klaus named the new element from the Latin word, Ruthenia, and mentioned Osann’s work, saying:

“I named the new body, in honour of my Motherland, ruthenium. I had every right to call it by this name because Mr. Osann relinquished his ruthenium and the word does not yet exist in chemistry”

ruthenium chloride is sometimes shown as red, but it’s actually black

Klaus died of pneumonia in 1864, and the study of ruthenium in Russia more or less stopped for the best part of seventy years, not restarting until the 1930s. The element is now known to harden platinum and palladium alloys, and is used in electrical contacts as a result. When just 0.1% is added to titanium it forms an extremely corrosion-resistant alloy which is particularly useful in seawater environments.

Ruthenium and its compounds have lots of other uses, too, including cancer treatments and in catalysis. Ruthenium(VIII) oxide, a colourless liquid (just: its melting point is 25 oC) forms brown-black ruthenium dioxide in contact with fatty oils; because of this property it’s used in forensics to expose latent fingerprints.

This Swarovski necklace has been plated with ruthenium

One of the most vibrant ruthenium compounds is the dye, “ruthenium red”, which has been used as a biological stain for over 100 years. It has the complicated formula [Ru3O2(NH3)14]Cl6 and is made by reacting ruthenium trichloride with ammonia in air, which might explain why pictures of ruthenium trichloride sometimes show a red substance, when it’s actually a rather boring black.

One place where you might have come across ruthenium in everyday life is jewellery: the metal’s hardness, high corrosion resistance and unusual, not-quite-metallic grey-black finish make it popular choice. Pure ruthenium is expensive though, so it’s almost always plated onto a cheaper base metal.

And now, one last picture to mark my ruthenium-day: check out my fabulous chemistry-themed birthday cake (thanks, Mum!), made by the Cotswold Cake Room. How amazing is this?

Normally at the end of my blog posts I link to my ko-fi account, but this time, instead, if you’re feeling generous please consider donating to my birthday fundraiser to raise money for Alzheimer’s Research UK.

The fundraiser is running through Facebook, which I appreciate doesn’t suit everyone — if you’d like to donate without going via that particular social network, there’s a link to donate directly here. Do drop me a comment below if you do, so that I can say thank you x

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2019: The Year of the Periodic Table

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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