Elemental
Page 8
In Iron Man 2 Tony Stark is looking for an element to power his suit before it kills him from palladium poisoning. No appropriate metal exists, however, so in order to save the movie and defeat Mickey Rourke, he manufactures a new element using a UV-laser and his raw charismatic charm.15
We already know there are no elements missing from the periodic table so Stark’s unnamed one is going to be made from huge atoms, and therefore massively radioactive. My screenplay for Iron Man 3 centered around Tony Stark vomiting into a hospital bucket for two hours as radioactivity slowly destroyed his internal organs. For some reason, the script they eventually chose went a different way. Their loss.
In 1940, Edwin McMillan decided to pre-empt Tony Stark and make a new element for himself. He took a lump of uranium and fired a stream of high-energy neutrons at it until some were absorbed. A uranium nucleus can accept a neutron but doing so makes it unstable.
In order to lose some energy, one of the neutrons has to undergo a beta decay, kicking out an electron and converting itself into a proton. The uranium atom now has an extra proton in place of a neutron so it’s not really uranium anymore. It’s element 93.
For fourteen billion years the ninety-third element didn’t exist in the Universe, and then suddenly, on Earth in 1940, it did.16
Uranium had been named after the planet Uranus, so McMillan named his element neptunium after the next planet in line. Later the same year, as part of the Manhattan Project, Glenn Seaborg managed to synthesize element 94. This one is a lot more stable than neptunium so, while neptunium was the first artificial element, Seaborg’s could actually be made in chunks big enough to hold. It’s a shiny metal with toxicity comparable to nerve gas, and Seaborg named it plutonium to keep with the planetary theme.17
Throughout the remainder of the Second World War and after, Seaborg went on to synthesize americium (element 95, named after America), curium (element 96, named after Marie Curie) and berkelium (element 97, named after Berkeley, California, where the research was carried out).
These experiments were highly classified as part of the war effort, but once it was over Seaborg was given permission to present his findings to the American Chemical Society on November 16, 1945. However, he accidentally spilled the beans five days earlier.
An avid popularizer of science, Seaborg was asked to appear on the children’s radio show Quiz Kids and answer questions about physics. When an eleven-year-old boy named Richard Williams asked him if people would ever make new elements (not realizing he was talking to the world’s leading expert on that very topic) Seaborg was unable to contain his excitement and blurted out the classified discoveries live on air, much to the annoyance of his superiors.18
Really though, can we blame him? He was surrounded by eager minds asking him everything he knew about his favorite topic. One might say he was in his element. I’ve been waiting for eight chapters to drop that joke.
COMPLETING THE TABLE
The periodic table is split into seven periods representing the seven orbital shells, and eighteen groups representing how many electrons occupy each one. As a result, the table has 118 spaces. With 92 occurring naturally, that gives us 26 blanks to fill.
Seaborg got lucky with his elements because they were all reasonably stable. Had he kept going he would have found things got a lot more difficult. Forcing nuclei to put on weight isn’t easy because the larger they get, the more repulsion there is between protons.
The best approach is to take samples of an already large element and bombard it with smaller nuclei in the hope that they get absorbed. In 1950, californium was made by firing alpha particles at curium, and einsteinium and fermium were made in 1952 via a similar route.
We’ve also used this technique to create lower-numbered elements, which are normally rare in nature. Francium is the second scarcest element on the table (behind astatine) with approximately 30 g available in the Earth’s crust. But if we fire an oxygen atom at a piece of gold we can generate it.
We can also create supplies of technetium, element 43, which has an unstable nucleus and doesn’t normally last. It’s worth doing because it makes up 80 percent of the world’s medical tracers, injected into the body to track blood flow.
Making artificial elements is a precision operation, of course. Fire the nuclei too slow and they bounce off; go too fast and everything shatters. But over the last half century we have edged closer and closer to a full table.
We’ve fired carbon atoms at americium and curium to make mendelevium and nobelium. We’ve fired neon at einsteinium and made lawrencium. We’ve fired neon again at plutonium and made rutherfordium.
By the early 2000s, we had dubnium, seaborgium, bohrium, hassium, meitnerium, darmstadtium, roentgenium, copernicium, flerovium, and livermorium, leaving only four to be discovered. The missing numbers were 113, 115, 117, and 118.
At this point, the bottom-right of the periodic table looked like a row of punched teeth. Then, in November 2016, the International Union of Pure and Applied Chemistry announced the successful synthesis of nihonium, moscovium, tennessine, and finally oganesson. The periodic table was finally complete.19
Some of this might seem like pointless playing around but many of these artificial elements can be useful. You probably have a sample of americium, element 95, in your home right now. At least, I hope you do.
Americium emits alpha particles constantly so if you put it in an open circuit, the charged particles can fly across a gap to a receiver and complete the circuit without wires. When flecks of smoke or dust float into this gap, the alpha stream gets blocked and an alarm triggers. This is how your smoke-detector works.
THE END OF EVERYTHING
Now that we’ve got all the way to element 118 and completed the table, could we go further? The honest answer is that we aren’t sure. Oganesson represents the filled seventh shell, but there might be an eighth or even a ninth shell.
Seaborg suspected the periodic table might stop when we reach element 126 because it’s a magic number and beyond that the proton-repulsions may become too powerful, no matter how many neutrons we include. It has even been called unbihexium as a placeholder name.20
Other physicists speculate that we could go on to create a ninth period or a tenth and an eleventh without limit. We don’t know enough about the nucleus to say for sure, so the only sensible thing to do is try. And that’s the whole point of science: to see what might be possible.
CHAPTER NINE
Leftists
THE EASIEST NOBEL PRIZE EVER EARNED
Twenty years ago, if you’d asked a scientist what the most electrically conducting element was, they would have said silver. The only reason we don’t use it in electronics is that copper is cheaper.
Then in 2004 two physicists won a Nobel Prize by making another element conduct better with a piece of Scotch tape.
Russian physicists Kostya Novoselov and Andre Geim (who you might remember as the scientist who made frogs levitate in 19971) were working with graphite, the soft form of carbon used to make pencil cores. Because graphite is a brittle material it tends to become flaky and the scientists down the hall were using Scotch tape to clean their samples. By sticking tape to the graphite and peeling off the excess dust, the result was a shiny new surface.2 It was watching this that gave Novoselov and Geim an idea.
If you stick the tape to a lump of already cleaned graphite you can extract a single layer of carbon, no more than one atom thick. This peculiar substance, which they named graphene, is arranged like a chicken-wire fence of carbon atoms and it has many unusual properties. Not only is it two hundred times stronger than steel, it is also transparent and can be used as a sieve to filter the salt out of seawater.3
On top of all this, graphene has an electrical conductivity better than silver. We measure electrical conductivity in units called siemens (pronounced zeemuns) per meter. Silver has a conductivity of 60 million siemens per meter and graphene clocks in even faster, although nobody has been able to agree on a
definitive reading yet.4 What makes this surprising is that carbon isn’t a metal and it’s usually only metals that conduct. Something very weird is going on.
WHAT IS A METAL?
When we hear the word metal we all picture the same thing: Ian “Lemmy” Kilmister, the bassist/vocalist of English rock band Motörhead. May he rest in peace.
After that we tend to think of grayish solids that are hard and shiny. What we’re really thinking of when we do so are steel, titanium, aluminum, and chromium, the four metals that dominate our everyday experience, but metals have all sorts of other appearances and properties.
Bismuth forms labyrinthine square crystals, which glisten like oil on a puddle, while lutetium and thulium are found in fibrous clumps that look like pieces of torn beef. Niobium is a dull silver when first isolated but pass an electric current through it and it becomes rainbow-colored.
Some metals show magnetism (iron, cobalt, nickel, terbium, and gadolinium) while some are not magnetic themselves, but will reinforce the property in those five (neodymium). Some metals will remain solid when heated to over 3,000°C (tungsten) while others will melt in the palm of your hand (gallium). Their reactivity also ranges from gold, which won’t even corrode in acid, to erbium, which explodes if you warm it gently.
With such a broad spectrum of behavior, what is it that unites them all? The answer is that a metal is an element that will always conduct electricity. Sure, carbon will conduct in the graphene state but metals will conduct no matter what state they’re in.
In order to understand metal chemistry, we need to understand electricity and that story starts in ancient Egypt.
THE FIRST PHARAOH
In 3100 BCE the kingdom of Egypt was united for the first time under the rule of Narmer, the original pharaoh. There’s a lot of debate around Narmer’s true identity but we know the meaning of his name with some confidence. Narmer, translated into English, means “angry catfish.”5
It may seem odd that a pharaoh would adopt the name of a river fish, but in Egyptian culture catfishes were the lord-protectors of the Nile and one of the most revered creatures in the world.
It’s true that most catfish are useless monstrosities but the breed found in Egypt is special. Its Latin name is Malapterurus electricus, which means “electric catfish.”
Like the electric eel of South America, this creature harbors a special organ that gives it the ability to deliver 400-volt shocks to anyone touching its skin. Records of the electric catfish are the earliest examples we have of electricity and it was five thousand years before humans could boast a similar control of the phenomenon.
SHOCKING
It is a crying tragedy that the man who discovered electricity is usually forgotten. The Greek scientist Thales (the one who fell down the pit) had already made the discovery that rubbing pieces of amber with wool caused them to gain a crackly property, which sparked under the right circumstances, but the discovery of what we think of as electric current goes to an English experimenter named Stephen Gray.
One of the reasons why Gray’s work was overlooked is that he made the mistake of asking another scientist to help him develop it. That scientist was John Flamsteed, who happened to be a mortal enemy of Sir Isaac Newton.
Newton was a socially cruel, even malicious character who used his position as head of the Royal Society to discredit and bury the work of people he disliked, including Flamsteed.6 Consequently, much of Flamsteed and Gray’s achievements were ignored. It has to be said that while Newton was one of the greatest minds in history, he was also a jackass sometimes. So, let’s redress the balance and give Stephen Gray his due.
Born in 1666, Gray worked as a dyer for most of his life and only indulged science as a hobby. He discovered electricity one night in his bedroom at the age of forty-two while playing with a crude instrument used to generate static—a tube of glass.
Static generators had been around since 1661, invented by the German politician Otto von Guericke, but Gray didn’t have the money for such lavish equipment. He had to make do with rubbing a glass rod on rabbit fur and tapping it on whatever was around in the hopes of creating a shock.
Gray was curious about the fact that if you put the rod on the ground after rubbing it, it seemed to lose its electricity and wouldn’t shock anything again until recharged.
On this particular night he decided to jam the end of the rod into a piece of cork and discovered that when he tapped the cork-tip against a pile of feathers, it sparked. The glass had been rubbed but the cork was somehow able to transfer the electricity through itself. Whatever electricity was, it could flow.
Excited by this result, Gray built a silk harness from his ceiling so objects wouldn’t touch the ground, and began testing things to see if they would transfer electricity. After trying vegetables, string, coins, and anything else he could find, Gray began dividing everything into two categories: insulators, which wouldn’t transfer electricity, and conductors, which would.7
The best conductors turned out to be metals, located on the left side of the periodic table. These were so good at electric transfer that Gray was able to pass a shock down nearly 250 meters of wire suspended from his bedroom window.8
Metals even conducted when pointing upward, which meant that whatever electricity was, it wasn’t influenced by gravity. Electricity would still go into the ground, of course, but it’s obviously not because of gravitational attraction. Instead, the planet itself was a conductor, which electricity will flow through given the chance.
Even more surprising among Gray’s results was the fact that humans conducted electricity. By suspending a young boy from his silk harness, Gray was able to charge him and generate sparks from his face. This became the basis of a popular sideshow exhibit called “The Flying Boy” in which spectators could tap the floating youngster’s fingertips and receive a shock.9 All in the name of science.
The secret to this exhibition is that human skin is usually coated in a fine layer of saltwater in the form of sweat, allowing electricity to zap across its surface. When the spectators, who were connected to the ground, touched the charged boy, the electricity would flow over their skin and into the earth, creating the shock effect.
We know from Chapter 3 that electricity is made from electrons, so to explain all these behaviors we must turn once again to the Schrödinger equation.
STATIC
As we know, electrons occupy orbitals around their nucleus and atoms brought together can mix orbitals to form molecules.
Static electricity happens because this orbital mixing is not a rare occurrence. In fact, it happens when any two surfaces meet. As you sit on your chair right now, a few of the chair’s electrons are forming temporary bonds with the electrons in your clothes (at least I hope so; please don’t read my book naked).
When you stand up, most of the electrons return to their original atoms and the bonds are severed. Chair electrons go back to the chair and clothes electrons return to you. We refer to this as the triboelectric effect and it’s a weak form of chemical bonding.
The thing is that some molecules are better at holding electrons than others and when it’s time for the bonds to break they don’t always return to their original configuration.
The molecules that make up human hair, for instance, are poor electron-holders whereas rubber is very good at it. If you put a piece of rubber such as balloon against your hair some of your hair electrons realize they’re happier sticking with the rubber and they transfer across.
There’s no limit to how many electrons you can cram onto a molecule so the rubber is happy to accept these travelers. When you separate from the rubber, some of your hair electrons stay on the surface of their new home and a charge imbalance arises.
The rubber and hair originally had no overall charge because the electrons and protons canceled each other but, if we transfer electrons from hair to rubber, things look different. The balloon finds itself holding an electron surplus while your hair has an electron deficit.
The surprising thing is that transferring electrons this way leads to greater stability. It sounds wrong because the rubber has stolen something from your hair, but remember that stability in quantum terms means “things have already lost energy to get to this state.” Two molecules can be a lot more stable if they split, the same way a house of cards is a lot happier falling to pieces.
The overall result is that when you rub a balloon on your hair it steals somewhere in the region of two hundred billion electrons. That sounds like a lot but it’s less than a trillionth of a percent of the electrons your body has in total.
If the balloon is now brought near a good conductor (like a piece of metal or the ground), the electrons are offered an even better deal and will flow into it, spreading as far away from each other as they can. Except this time we’re not talking about little bonds being formed, we’re talking about all the electrons jumping at the same time, creating the infamous static shock.
When Stephen Gray rubbed the glass rod, he was depositing electrons on its surface from the rabbit fur. Glass is an insulator so it can store electrons on its surface and won’t allow them to flow from one end to another. The cork was a conductor, however, so the electrons were able to travel through it and into the ground. His experiments with wires were an extension of the same principle.
WHY DO METALS CONDUCT AT ALL?
As you read from left to right across the periodic table you’re gradually increasing the number of protons in the nucleus. The more proton charge you have, the more electrons will be pulled inward and the smaller your atom becomes, meaning we see a decrease in atom size along each row.