by Tim James
Atoms on the left are therefore big and diffuse with great, floppy orbitals. Their electrons are also a long way from the nucleus with nothing much keeping them in place. This makes them ideal for sharing electrons with other atoms since the electrons have very little incentive to stay put.
When you get these bulky atoms together, their orbitals start mixing not just on a one-to-one basis but over the entire population. The atoms are so happy to share that when you solve the Schrödinger equation to describe millions of metal atoms, the result is a kind of mega-orbital—a turbulent free-for-all, which physicists call “the electron sea.” This network of overlapping orbitals means electrons can easily slosh from one side of the structure to the other.
Touch any piece of metal and beneath your fingertips you’ve got a swarm of electrons flitting back and forth at will. These movements are random but if we can persuade the electrons to travel in one direction at the same time we have an electric current.
In smaller molecules, formed by elements on the right, gaps between the orbitals make it hard for electrons to move, so they won’t conduct. That doesn’t mean, of course, that it’s impossible to force an electron through an insulator. Teflon, the most insulating material on Earth, can still be made to conduct but you need a fierce amount of energy to persuade the electrons to hop across the orbital gaps.
A substance with a conductance over 1 million siemens per meter is classified as a conductor while a substance below 0.01 is an insulator. Admittedly there’s a huge gap between 0.01 and 1 million siemens per meter, but very few substances fall in this region. Those that do are deemed “semi-conductors.”
THE WEIRDO
Whether a substance is a solid, liquid, or gas depends on how much the particles are attracted to each other. Oxygen molecules have little interaction because they’re stable, making oxygen a gas at room temperature. It can be turned into a liquid by cooling it down (fun fact: liquid oxygen is blue) but under standard conditions it tends to spread out.
By contrast, metals are good electron sharers, meaning their orbitals overlap and they clump together forming a solid, with the obvious exception of mercury, the metallic liquid. A full explanation for mercury’s liquidity requires knowledge of Einstein’s theory of special relativity, but we can get the gist without worrying about that.
Like other metals, mercury’s orbitals stick out in many directions like petals on a flower so it can conduct, but it’s in a funny position on the table. It sits on the bottom row, making it huge, but over on the right-hand side meaning it has a lot of protons pulling the orbitals inward. The result is that the orbitals are extended enough to overlap but not quite enough to hold the atoms together.
Move to the right and you increase the proton number, causing the atoms to pack together better, resulting in a solid. Move to the left and the orbitals overlap better, also resulting in a solid.
Mercury atoms are just too weakly attracted to stick together, but just attracted enough to allow electrons to hop from atom to atom. The result is that mercury is a conducting element and therefore a metal but it’s unquestionably the worst metal on the table.
THE OTHER WEIRDO
When electrons travel through a piece of metal they don’t move in perfect lines. The nuclei vibrate and the inner orbitals interfere with the outer ones. The result is that conductivity never happens perfectly and we call the collection of things that slow it down “resistance,” measured in ohms. The energy electrons are given as they are pushed through the metal is called voltage (measured in volts). These things together give rise to the overall electron flow.
If we think of voltage as a fist squeezing the end of a toothpaste tube, the resistance is the diameter of the tube and the actual amount of toothpaste that comes splurging out is what we call current, measured in amperes (amps for short).
A watch battery delivers electrons into the watch with an energy of about 1.5 volts. The resistance of the circuit slows it down and we end up with a current in the region of five-millionths of an amp (0.000005 A).
For perspective, a bolt of lightning packs around 100 million volts. This electricity is forced through the air, however, and the overall current ends up at around 5,000 amps by the time it reaches the ground. Passing electricity through non-metals like air involves a lot of energy being lost.
Graphene’s conductivity is therefore very strange. Carbon is a non-metal most of the time but when it is arranged in the thin wafers of graphene it starts to conduct.
It happens because the atoms in graphene are arranged in flat hexagons with each atom bonded to three others. Since carbon has an available four electrons in its outer orbitals, each atom has a spare one that isn’t involved in bonding. This electron can move from atom to atom with hardly any obstruction, so even a small voltage will produce a lot of current.
Where graphene differs from metals is that it is almost two-dimensional. In a metal, electrons can change route and go exploring in all directions but in graphene there are less places to go. It is practically a flat plane, meaning electrons have no possibility of moving up or down, making them more likely to stay on track.
ELECTRICITY AND YOU
In 1886 an American human rights committee decided that execution of criminals by hanging was inhumane and a new method of capital punishment was needed. One of the people on the committee was Alfred Southwick, a dentist from New York who had already designed an electrocuting chair several years previously. Southwick’s idea was approved and testing began, endorsed by none other than Thomas Edison himself.10
At the time, there was a battle going on over which type of electricity the United States should adopt. Edison had put a lot of money into battery-based electricity and needed to find a way of tarnishing the reputation of magnetically generated electricity, favored by his rival George Westinghouse. His solution was simple, if a little gruesome.
In the most morbid marketing strategy ever employed, Edison insisted that the newly designed electric chair be configured to run on Westinghouse’s electricity, so people would associate it with death.
He tested the chair on stray animals in his workshop and is on record as having killed dogs, cats, birds, a horse, and a circus elephant named Topsy (he was considerate enough to film that last one, and you can watch it for free online if you’re into that sort of thing).11
Soon after, the electric chair was rigged-up for its first victim, William Kemmler, in 1890.12 Kemmler took over four minutes of continual electrocution to die, with the procedure stopping halfway through until someone screamed, “Great God, he is alive!”13 Humane indeed.
The key to the electric chair is making sure the human body is part of a circuit, which is actually quite difficult to do. Despite what Saturday morning cartoons claim, you’re not very easy to electrocute.
If you’re ever unfortunate enough to be hanging from a power line you may feel a tingling in your fingers, but you’re in no real danger. Once the electricity has filled all the available orbitals on your surface there is nothing else it can do.
If, on the other hand, you somehow connect to the ground then you’re not a cul-de-sac anymore: you’re a pathway and the electricity will use it. If electricity goes onto you, you’re fine, but if electricity goes through you, you’re in trouble.
The human body is a fairly decent conductor (you’re a bag of salty water) but to complicate matters your skin is an excellent insulator. Dry skin has a resistance of about 100,000 ohms, although wet skin absorbs water into its pores and the resistance drops to around 1,000 ohms.
It’s also worth pointing out that once electricity enters your body it will travel along the easiest path available. A tiny amount may go exploring, but you could pass thousands of amps through your hand without dying. It would still hurt, so don’t do it, but you wouldn’t be in mortal danger.
The only time electricity becomes lethal is if it passes through your heart, lungs, or brain for a sustained period of time.
The way your heart works
is that the muscular outer layer is given a short electric shock of around 0.0000012 amps every second, which causes it to contract, squeezing blood to your body. Afterward it is allowed to relax and reopen, taking in more blood, before the whole thing is repeated.
If a current is pushed through the heart for a long time, however, it squeezes tight and doesn’t reopen, meaning it can’t take in a fresh load of blood. That’s why people can survive lightning strikes but not the electric chair. The electricity of lightning may pass through your heart, but it does so for a short time only and your heart is able to return to normal. If you keep the current flowing, you essentially give the person an artificial heart attack.
Surprisingly (or perhaps not) very little research has been done on how much current is needed to make the heart do this. The approximate guidance, based largely on anecdotal evidence and a bit of bioelectrical theory, suggests that around 0.05 amps is required to kill a person.
The electric chair worked by passing a current of between 1 and 7 amps through the body depending on the state legislation. That’s over twenty times the lethal dosage.
Typically, the two live ends of the circuit would be connected to the scalp and ankle so the current would pass through the brain, heart, and lungs together, guaranteeing the malfunction of at least one of them and ensuring a warm death. Have a nice day.
CHAPTER TEN
Acids, Crystals, and Light
A BARREL OF HORRORS
In March 1949, English newspapers reported one of the most gruesome crimes to occur in British history since those of Jack the Ripper. John George Haigh, who the Daily Mirror had referred to as the Vampire Murderer on March 3, was taken to court and charged with six counts of pre-meditated homicide. What made them particularly ooky wasn’t the murders themselves but the way he disposed of the bodies.
After drinking glasses of their blood, Haigh loaded each body into a 40-gallon drum, which he topped with concentrated sulfuric acid and left for two days. The remaining sludge was poured into a drain behind his workshop, earning him his other colorful nickname, the Acid Bath Murderer.
Acids capture people’s imagination because they are the standard “nasty” chemicals, capable of chewing through a human body and destroying any evidence the person was ever there. The only reason Haigh was caught was because the solution of his final victim, Olive Durand-Deacon, still contained part of her plastic denture, which her dentist identified.
Haigh was executed by hanging on August 10, 1949. He claimed to have other victims but they are unidentified to this day because the bodies were disposed of so perfectly.1
IT BURNS, IT BURNS!
An acid is a substance whose molecules fall apart in water to produce free-floating protons. Protons are the charged particles inside a nucleus, shielded most of the time by their electron orbitals, but if they get released when their parent molecule dissolves they can cause untold damage.
A rogue proton is a concentrated lump of charge and will pull electrons toward itself at any cost. Things like glass or plastic have strong bonds between atoms so acids aren’t usually able to react with them, but any chemical with loose bonds, including the ones in your body, will be pulled apart.
An acid can be thought of as a proton juice and the easiest way to generate a solution of protons is to make sure your starting molecule contains hydrogen. Hydrogen is the simplest element, consisting of one proton and one electron, so if its electron is more interested in the other atoms of the parent molecule, the proton will drift away.
Take hydrogen chloride. Each molecule consists of one H atom and one Cl atom, giving it the formula HCl. The chlorine atom is very good at holding electrons, better than the hydrogen, so the bond between them isn’t a fifty/fifty share—it’s lopsided like so:
Put the whole thing in water and the two atoms will separate with chlorine keeping all the electrons and hydrogen being left essentially naked.
This lonely hydrogen proton drifts away, waiting until some other molecule with which it can react comes along. We have generated hydrochloric acid, the one in your stomach, capable of dissolving bone.
THE STRONGEST ACID
We measure how strong an acid is by how willing it is to let go of a proton. The numbers involved spread over an enormous range and we use something called the pKa scale to measure it. The scale works the same way as the earthquake Richter scale where each number is ten times greater than the one before it. The scale also works backward for reasons we don’t need to worry about (see Appendix V if you’re curious). So, the lower the number, the stronger the acid.
Household vinegar has a pKa of 5 whereas oxalic acid, the one in rhubarb, is closer to 4, making it ten times more potent. Then there’s chromic acid, a powerful industrial agent, with a pKa of 1—three places lower down the scale than oxalic and therefore one thousand times stronger. For context, you can eat oxalic acid and feel fine but chromic acid will set fire to living tissue.
The concentrated sulfuric acid Haigh used to dispose of his victims scores a −3 on the pKa scale, seven numbers lower than vinegar and therefore ten million times stronger.2 That’s another way of saying that sulfuric acid is ten million times better at releasing its proton than vinegar. But if we can create molecules with absolutely no interest in holding their hydrogen, we end up with a class of chemicals on our hands called superacids (well, hopefully not on our actual hands).
Perchloric acid has a pKa of −10, which is ten million times stronger than concentrated sulfuric and triflic acid has a pKa of −14, one hundred billion times stronger.3 And that’s not even touching on magic acid (actual name), which will dissolve even candle wax.4
If you scan around the internet, most popular science websites tend to report the strongest acid in the world as something called fluoroantimonic acid, boasting a pKa of −19. That’s ten quadrillion times stronger than sulfuric. It’s occasionally used in the electronics industry to etch equipment, but it doesn’t really deserve the gold medal. That goes to an acid so strong it has only been synthesized once in recorded history.5
An acid’s job is to kick hydrogen away so the best acid will be one where the other atoms don’t want to bond with it in the first place. And there’s no better atom for that than helium, the least reactive element on the table. If you can force hydrogen to bind with helium, you’ve created the weakest bond it’s possible to get and it will fall apart instantly.
In 1925, the chemist Thorfin Hogness managed successfully to brew a microscopic quantity of helium hydride that possesses a pKa of, brace yourself, −69.6 That’s so strong there isn’t even a word to describe how much better it is than sulfuric acid.
The non-reactivity of helium is also responsible for another record-breaking property it possesses: liquid helium is the most fluid liquid in the Universe. When a sample of helium is cooled to around –269°C, the atoms lose their movement energy and settle into liquid form. In most liquids the atoms still interact with each other a little, but in helium they keep to themselves.
If you take a cup of liquid helium and stir it once, it will keep spinning forever. Any other liquid would interact with the container and be slowed down but liquid helium doesn’t feel friction and will keep spinning until the end of time.7
Wouldn’t that constitute a perpetual motion machine, though? The answer is that if we tried to put something like a propeller into the swirling vortex, the helium would just flow around it. The only way to get the liquid helium to work on something would be to warm it up, and as soon as you do that the superfluidity is lost.
Liquid helium also happens to defy gravity. Air pushes down on everything at atmospheric level and near the edges of a container some liquids are able to creep up the sides because they’re being pushed by air on one side but not the other.
Most liquids are self-attracting enough to stay together and not begin climbing the walls but liquid helium isn’t most liquids. Helium will move up the sides of an open container and creep its way out, emptying the vessel as if
it had a desire to escape.
In order to understand the surreal properties of liquid helium and helium hydride, we’re going to travel to the right side of the periodic table. The realm of the non-metals.
SELFISH CREATURES
Most of the spectacular and violent reactions in chemistry take place in the non-metals because they’re so greedy. As we’ve already seen, metals are big and have friendly, overlapping orbitals, but atoms on the right are small and grip their electrons tightly.
The most reactive element is fluorine, which we met in Chapter 1 when it was setting fire to water. A sparse yellow gas, fluorine needs to be transported in dense steel and bulletproof glass because it will rip the electrons out of anything else it touches.
Because it’s so electron-hungry, a molecule of two fluorine atoms will be perfectly symmetrical as the electrons are shared between them. If you bond it with a metal such as cesium, however, the bond is uneven, with fluorine getting the lion’s share of electron density. It’s similar to the way hydrochloric acid molecules are arranged—non-metals always win because they don’t like to share.
This electronic exchange means cesium atoms become electron deficient while the fluorine atoms become electron rich. It’s not really correct to call them atoms anymore since they aren’t neutral units so we refer to them as “ions” instead.
Ions are still sharing electrons but it’s such an uneven bond we usually just imagine cesium losing electrons and fluorine gaining them.
You’ll see diagrams of ionic bonds in which the particles are drawn like balls packed together, such as in the diagram on page 122 (top). That’s not strictly correct, but it helps keep track of where the ions are and how they’re arranged. The diagram at the bottom gives a slightly more accurate picture.
