The Butterfly Molecule

Jonathan James

If you cast your mind back to chemistry class at school, you’ll probably remember learning about various types of atomic bonds. Typically, we think about the way atoms bind to one another in a couple of ways – ionic bonding, where oppositely charged ions are held together by electrostatic interactions, and covalent bonding, in which electrons are shared between atoms. For a long time, these looked like the only types of bonding that could exist under our current understanding of how atoms bind one another, but a recent discovery has unveiled a whole new type of bonding that seems to defy our understanding of chemistry.

Let’s quickly recap what we know about atoms. In the traditional model, atoms are made up of a positively charged nucleus, made up of protons (which give it its positive charge), and neutrons. This nucleus is tiny, and the clear majority of the atom’s size is empty space. Surrounding the nucleus are negatively charged electrons, which orbit in ‘shells’, a bit like planets around the sun (but not really… That could be an article all by itself!) Typically, atoms take up a volume so small, that you could fit 200,000,000,000,000,000 of them inside the dot on this exclamation point!

Recently, however, scientists have been able to confirm a theory that they’ve had since 2002. The existence of ‘Rydberg molecules.’ Affectionately referred to as ‘Butterfly molecules’ because of the butterfly like distribution of the orbiting electrons, Rydberg molecules are enormous. In fact, at a millionth of a meter across (huge for an atom!), they are about the same size as an entire E. coli bacterium. Their electrons are anywhere from 100-1000 times further away from the nucleus than they should be. At these distances, the electrons become ‘super electronically excited’, which allows them to act like a lasso, grabbing nearby atoms and forming weak interactions with them.

The researchers created the molecules by super cooling Rubidium gas to a just above absolute zero, before exciting them into their Rydberg state using lasers. They then kept the atoms under observation, looking for changes in the frequency of light that they would absorb, as this would show that a bond had been formed. Eventually they discovered that they had indeed triggered the formation of these butterfly molecules.

But why should you be excited about this discovery? After all, it’s just another type of dull chemical bond that kids will be forced to learn about, right? Actually, there is a lot of excitement around Rydberg molecules and how they might be used in nanotechnology and small scale electronics to make them much more efficient. There are even hopes that they might be used in quantum computing, pushing technology even more into the future!

Metallic Hydrogen: 80 years in the making

 

Ashley Carley

Rocket fuel, lightning-fast supercomputers and levitating trains are just three uses of the newly discovered metallic hydrogen – if, the Harvard scientists say, everything goes to plan.

Hydrogen is the lightest and most abundant of all the elements. It forms two thirds of every drop of water, and almost 75% of the gas in the Sun’s core. Alone, hydrogen is most often found floating around in its gaseous phase, but it has been predicted a metallic form may exist when exposed to intense pressure.

Two physicists at Harvard University claim to have isolated this incredibly rare form for the first time, in a paper published this week. By squeezing solid hydrogen between two diamonds at temperatures well below freezing, the researchers created pressures larger than those found at the centre of the Earth. In these conditions, the hydrogen atoms began to share their electrons. Using this new electron cloud, they could conduct electricity.

Isaac Silvera, who made the discovery alongside his colleague Ranga Dias, recognises the importance of his achievement, calling it the “holy grail of high-pressure physics.”

This breakthrough has been a long time coming; it has been over 80 years since Eugene Wignar and Hillard Bell Huntington made the first predictions about metallic hydrogen. Since then the goalposts have continually shifted. Estimates of the pressure required to make the substance have been continually revised upwards, from 25 gigapascals (GPa), 250,000 times above atmospheric pressure, in 1935, to the most recent estimate of 400-500 GPa.

Each time the prediction changed, it moved out of the range scientists were capable of recreating in a lab environment, making it somewhat of a carrot on a stick for researchers in the field. Jeffrey McMahon, theoretical physicist at Washington State University, told New Scientist that if the results were reproducible, the recent experiments had solved “one of the major outstanding problems in all of physics.”

It wasn’t easy – the synthetic diamonds had to be flattened, polished and heated to remove any imperfections that could result in cracking. They were then covered in alumina, an extremely hard material made from aluminium and oxygen that hydrogen could not leak through. The two diamonds were then crushed together with great force, and Dr Dias watched as the hydrogen between them turned from clear to black, until it began to shine. The force required was 495 GPa – higher than the pressure at the Earth’s core. Dr Dias then called Professor Silvera, and they took the measurements that would confirm their discovery.

The next step is to see if it retains its structure when compression is relaxed. Some predictions suggest it will be too unstable to survive at room temperature, and will gradually decay, although others have more hope. Graphite forms diamonds under high pressures and temperatures, but when the sources of compression and heat are taken away – the diamond remains. Scientists are hoping metallic hydrogen could act the same way once released from its diamond vice.

If it does, its potential applications are exciting. If the amount of energy used to create the metallic hydrogen can be released by breaking it down again, it could become the most powerful rocket fuel ever made. “We would be able to put rockets into orbit with only one stage, versus two, and could send up larger payloads, so it could be very important,” Professor Silvera says. Electronic systems would also be revolutionised, as “superconductors” could be made which reduce energy wastage in wires.

When Professor Silvera is asked what thinks will happen next, he responds “I don’t want to guess, I want to do the experiment.” After an 80-year wait, perhaps the suspense is great enough.

The Element of Surprise: Things You Didn’t Know About The Periodic Table

Dan Chesman

If you were to walk into any school science laboratory and not see a periodic table on the wall, I would eat my own underwear. This seemingly unordered array of squares in a sort-of-but-not-really-rectangular shape takes its mammoth foot and stamps on your tiny ant of an Excel spreadsheet. It’s probably the most concise bit of database compiling you’ll ever see. Some would say that it’s art.

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Almost as good as the periodic table.

Image Credit: Wikimedia Commons

Though many laid the foundations, it is Dmitri Mendeleev’s first incarnation of the periodic table that gets all the credit. According to the Royal Society of Chemistry, his arrangement of the properties of elements correlated almost perfectly with the atomic weight of the known elements at the time. He noticed there were gaps, and went on to predict the properties of the elements that filled these gaps. By 1886, scandium, gallium and germanium had all been discovered based on Mendeleev’s predictions, and his method forms the basis of the modern periodic table. What a hero.

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This story’s bearded hero, Dmitri Mendeleev

Image Credit: The Telegraph

But what about these elements? Chemistry is weird and wonderful (and also really irritating – ask any PhD student how their lab work went this week!) and the elements form the basis of all the funky little molecules that do all the cool stuff we love.

By far, the best and most versatile group of elements are the transition metals. These are the three rows sat in the centre of the periodic table, with scandium at the top right and mercury at bottom left, among a few additional ones in a fourth row. These elements are responsible for much of the colour we see in the laboratory, and their compounds do a whole host of important things: from catalysing the manufacture of cling-film (titanium compounds) to curing cancer (cisplatin, a platinum compound with two NH3 and two chlorine (Cl) groups arranged around a central platinum atom).

Did you know that sodium (Na) in your table salt (sodium chloride) will catch fire if you put a chunk of the pure metal in water? Move one element down, and potassium will explode. Move to the second bottom row, and a few grams of caesium might demolish your house. These elements, the alkali metals – named because their reaction with water forms an alkaline solution – ignite on reaction with water because they have one very loosely bound electron which they will do anything to get rid of. As you move down the group, the elements hold on to their electron more loosely and will throw it at whatever will take it with ever more ferocity.

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Colours in transition metal compounds

Image Credit: chemguide.co.uk

In stark contrast, one left of the top right of the periodic table, is fluorine. This is one short of a full shell of 8 electrons and if caesium were to throw its electron toward it, fluorine would probably rugby tackle it to the ground. Fluorine is massively reactive for precisely the opposite reason to caesium. It will do anything to steal an electron.  Get even a whiff of this stuff, and you’ll be on the floor in a heap.

What about the other elements? Did you know that humanity has created its own elements? The first was technetium, which can be found in any hospital, where it is used as an imaging agent. Others include flerovium and livermorium, as well as the new kids on the block: nihonium, moscovium, tennessine and oganesson. These last four were named as recently as June 2016!

Some of the more exotic and rare elements lie on the bottom two rows of the periodic table. These are known as the lanthanides and actinides, or the f-block elements. These do all kinds of cool things. Many of them are man-made, and some named in honour of famous scientists (einsteinium, fermium, nobelium…). The top row – the lanthanides – are used in many fields from medical imaging to lighting your TV. Gadolinium is used to enhance the contrast of MRI scans, making it possible to diagnose diseases such as cancer and brain tumours. Europium is found in old TVs to give a red colour, and americium (an actinide, the bottom row) is a key component in your smoke alarm.

What’s the best element though? They’re all in with a shout really, but purely for being the real element of surprise, the award goes to mercury.  It’s one of the most toxic things you can come across, and it has baffled scientists for years. It’s a liquid, one of only two in the periodic table, and a heavy metal. Based on its position, it should not be a liquid, and it’s only recently that scientists have come up with a plausible hypothesis as to why this is the case – relativity. Yet again, Einstein has the answer.