by Tim James
This type of bonding where things are arranged in a lattice framework gives rise to crystal properties. Starting at group 13 with boron, non-metals tend to keep their electrons in very specific places, forming grids with sharp edges. This brings us to …
SPARKLY CREATURES
Boron is the second-hardest element after carbon. Used in making glues and glass, it’s usually found bonded to oxygen and sodium in the form of borax crystals exported from Death Valley, California, the hottest place on earth.
Borax crystals have a ghostly white appearance and are mostly transparent, something you don’t get with metals. Because of the sea of electrons, light will bounce off the surface of a metal, making it opaque. Non-metals, on the other hand, hold their electrons in fixed orbitals with gaps, meaning beams of light travel through rather than getting reflected.
Depending on the angles between ions and the sizes of their orbitals, a beam of light can emerge from a non-metal looking very different to when it entered. As the light is bounced around inside the crystal matrix, it can lose or gain energy, changing color and giving the crystal a different appearance.
The most common crystals on Earth are based on silicon and oxygen in the form of SiO2. It’s the other elements mixed with them that give rise to the different minerals we find in the ground. A single hunk of rock (a conglomerate of mineral crystals packed together) can contain dozens of different elements and we have to extract them with acids or electricity.
In fact, most elements on the table were discovered by grinding up rocks and seeing what was inside them. The elements yttrium, ytterbium, erbium, and terbium, for instance, were all discovered at the same Swedish mine from a single type of rock.
The most prized crystals, though, tend to be based on oxygen bonded to aluminum rather than silicon. On its own, aluminum oxide is a white crystal called corundum with an appearance similar to table salt. But if a few chromium atoms get mixed in, you’ve got ruby. Replace the chromium with titanium or iron and you get sapphire.
Then the most precious crystals of all, diamonds, are made from carbon atoms forming a tetrahedral array, with each atom linked to four around it. And again, it’s the impurities that give the colors. A bit of boron and your diamond turns blue while a touch of nitrogen will give you yellow. Change the atoms and you change the color.
HIGHFALUTIN ELEMENTS
As we go across any row on the periodic table we’re dealing with atoms that house more and more protons. The electron orbitals get sucked in and, as a result, everything on the right is smaller and greedier.
Group 17 is where we get things like fluorine (sets fire to cotton wool), chlorine (a chemical weapon), and bromine (a toxic disinfectant). But when we get to group 18 something strange happens. The elements of this column—helium, neon, argon, krypton, xenon, and radon—are the least reactive on the table.
They are so reluctant to get involved with bonding that they were originally named inert gases. We have since learned that group 18 elements will mingle with others a little, but not if they can help it. As a result, these snooty substances are referred to as “noble” gases (other groups have names too, see Appendix VI).
We saw earlier that helium’s refusal to bond is what makes helium hydride the strongest acid in the world, so the obvious question is what are the most lifeless elements doing next to ones like fluorine and chlorine?
The answer comes from how electrons are distributed around the nucleus. Orbitals are fixed in certain shapes according to the quantum rulebook but they are also grouped at specific distances.
The first set of orbitals are huddled around the nucleus, but the second set are a great distance away. This outer set is repelled by the inner set and there is a no-man’s-land between them.
The diagram opposite shows the energy levels of the first and second orbital sets. For simplicity, we’re ignoring the orbital shapes because then our diagram would look like a plate of panda entrails.
We call these orbital groups “shells” and they are the reason for the periodic trend Newlands identified. As we go from one side of a row to the other, we are filling the orbitals of a particular shell. When a shell is full, we jump to a higher one and start filling that instead, starting a new line on the table.
The noble gases are the elements we get when we have completely filled a shell. Because every orbital of these atoms is full, there’s nowhere to put an incoming electron. The atoms are also small (they’re on the right-hand side), which means they hold their own electrons tightly and won’t donate to anything else.
Noble gases are therefore unlikely to accept electrons or donate them, making them bad at bonding. A few dozen noble-gas compounds have been created over the last few decades but it’s not a common occurrence.
It might seem that these elements are pointless and boring, but their refusal to react makes them useful. Take a light bulb. The filament inside is made from tungsten, which glows when electrified. The problem is that the tungsten gets so hot it would begin reacting with oxygen. To avoid this problem, we flood lightbulbs with argon instead of air so nothing reacts and the bulb can continue to do its thing.
We can also use noble gases to produce vibrant colors of their own. If you trap a sample of noble gas inside a glass tube and pass a current from one end to the other, the atoms will start vibrating. The electrons get pushed outward by the electrical energy, but they fall back immediately, kicking out specific beams of light.
Any other gases would start reacting and everything would rearrange to become stable. Since stable means no more energy is available, your light would switch off moments after you switched it on. But noble gases are so reluctant to bond they just keep jumping back and forth, emitting a steady stream of light. Neon makes the tube glow red, helium glows orange, argon glows blue, krypton glows green, and xenon glows turquoise. Neon was the first to be discovered so we refer to these harsh buzzing tubes of gas as “neon lights,” the kind you see outside store windows.
CHAPTER ELEVEN
It’s Alive, It’s Alive!
THE MOST TOXIC POISON
In 2006, the world’s media reported on the agonizing death of Alexander Litvinenko as he succumbed to polonium poisoning. What made the story so chilling, aside from the political overtones, was the minuscule amount of polonium needed to cause death. It was estimated that Litvinenko consumed less than one-hundredth of a gram and was dead within three weeks.1 Is polonium the worst thing you can have in your body?
Judging toxicity is not as straightforward as you might imagine. For starters, everyone metabolizes things differently. Nicotine alone turns into seven different chemicals depending on the person, which might explain why some people find it harder to quit smoking. They literally turn it into more addictive substances.
This means that if you poison a large group of people some will die and some will survive, purely by chance. In order to get around this, biologists use something called the LD50 value, the lethal dose guaranteed to kill 50 percent of a group. The number is given in mg/kg (how many milligrams needed to kill every kilogram of creature) and the lower the LD50, the more toxic the substance.
The LD50 of pure caffeine is 367 mg/kg.2 A baby duck, which typically weighs around 1 kg, could therefore ingest 367 mg of caffeine and have a 50 percent chance of living. An African bull elephant, on the other hand, weighs 5000 kg so you’d need about 2 kg of caffeine to be 50 percent confident of killing it.
It’s also difficult to quote accurate LD50 values for humans because the only way of obtaining them would be to poison a bunch of people and see how many died. Sadly, there have been cases of experimentation on unwitting suspects, but usually such studies aren’t common.3
Some animals can be seen as close approximations to humans but you run into the same problems. Different species metabolize things differently. Glucuronic acid is harmless to humans and used in cooking sauces but it’s lethal to a cat. Arsenic is toxic to us but when added to chicken feed it causes them to gain muscle ma
ss. Plus, there’s the well-known fact that theobromine in chocolate can kill a small dog, but all it does to humans is leave them with a sense of self-loathing.
The animals biologically closest to us aside from chimpanzees, which are not tested on, are rats. Whatever your ethical stance on animal testing, the fact remains that trialing a chemical on rats is the closest thing we can get to human data.
It’s also worth remembering that chemicals get processed differently depending on how they are absorbed. Some elements like holmium are toxic no matter how you take them, but something like indium is only dangerous if inhaled. (NB: probably best you don’t ingest either.)
All of these factors make it very hard to say what is the most poisonous chemical in the world. That’s probably a good thing, but since we’re on the subject we might as well look at some of the candidates.
Lead has an LD50 of 600 mg/kg while thallium has one of 32 mg/kg, making it twenty times more dangerous. Arsenic, the preferred poison of nineteenth-century novelists, has an LD50 of 20 mg/kg while phosphorus comes in at close to 3 mg/kg.4
If we go on toxicity alone, this makes phosphorus the most poisonous element, but if we include the effects of radioactivity polonium outranks it by a clear mile. Radioactive elements don’t just kill by interfering with the functioning of the body: they spit alpha particles (see Chapter 8), which essentially rip your cells apart.
Because of this additional mode of killing, polonium probably is the deadliest element. In fact, nobody knows what the LD50 of polonium is because experimenters are reluctant to work with it. Even its dust can kill you. But given the amount needed to kill Litvinenko, the LD50 is going to be very small.
If we start including compounds as well as elements, though, polonium is no longer that bad. Dimethylcadmium is often cited as the most toxic compound in the world, so toxic that a thousandth of a gram dissolved in a ton of water is lethal.5 But the crown really belongs to botulinum toxin, a chemical produced by the bacteria Clostridium botulinum.
There are several varieties given the names A to H, and it’s botulinum toxin H that is the worst. Only two-billionths of a gram are needed to kill a fully grown adult.6 Assuming the population of Earth is around seven billion, you would therefore need only 14 g (a teaspoon’s worth) to wipe out the entire species. And it kills you in a pretty nasty way, paralyzing you to death.
You can also dilute it down to low concentration and inject it into your forehead, paralyzing the muscles and preventing wrinkles. Botulinum toxin A (not quite as deadly) is used for exactly this purpose and is marketed under the trade-name of Botox®.7
THE ELEMENTS OF LIFE
In 1924, the head of the American Medical Association, Charles Mayo, published a tongue-in-cheek calculation showing that if you split a human body into piles of its constituent elements the total value would be around eighty-four cents.8 The iron from your blood would make a single household nail while the carbon in your proteins would make a small bag of charcoal, etc.
We did something similar in the introduction when we looked at the chemical formula for a person. It’s a powerful reminder that the atoms that make up our bodies are no different to the atoms that make up the contents of our kitchen.
A lot of people seem uncomfortable with this notion. I once saw a magazine ad in which a worried customer is reassured by a scientist that their ice cream “contains no 4-hydroxy-3-methoxybenzaldehyde, only natural vanillin.” What the writers of the advertisement didn’t seem to realize is that 4-hydroxy-3-methoxybenzaldehyde is just the chemical name for vanillin. It would be like saying “this drink contains absolutely no H2O, only water.”
During the Middle Ages, everyone thought living creatures were made from magical “essences” different to non-living things. It was a belief called vitalism, but like most ancient quackery the cracks were beginning to show by the Renaissance.
In 1745, Vincenzo Menghini burned human organs to ash and discovered that you could extract iron powder from the remains with a magnetized knife.9 He concluded that humans had to contain the base metal iron and that perhaps we weren’t made of magical ingredients after all.
In 1828, Friedrich Wöhler went even further by manufacturing urea from cheap lab chemicals.10 Urea is the main component of urine and therefore was assumed to be beyond human understanding. Wöhler showed it to be a bog-standard molecule with the formula CH4N2O.
Whether you like it or not, the elements used in living biology are no different to those used in sterile chemistry. A strand of human DNA contains 204 billion atoms, all of them carbon, hydrogen, oxygen, nitrogen, or phosphorus. There’s no additional “essence” to make it special.
The iron Menghini discovered is used in blood to bind oxygen molecules and transport them to the various organs. When the oxygen gets to where it’s needed, enzymes and proteins containing chromium, molybdenum, copper, and zinc help store it, while manganese holds harmful atoms in place before they cause damage.
When a woman is pregnant she spends nine months breaking down food and reconstituting the atoms into a baby. The calcium in milk becomes the calcium in your bones, the nitrogen in potatoes becomes the nitrogen in your skin, and the sodium in salt becomes the sodium in your brain. In a very literal sense, we are what we eat.
It’s not just animals either. Plants use magnesium to absorb sunlight and vanadium or molybdenum to bind nitrogen from the soil, a crucial nutrient in growth. It doesn’t matter what the biological system is, you’ll find every bit of it on the periodic table.
I’ve occasionally heard people referring to biology as applied chemistry because of this deep connection, but this isn’t fair at all. Biology is just chemistry at its most wonderfully elaborate.
But it comes at a price. Since we are made from the same stuff as the world around us, that makes us vulnerable to the same malfunctions.
STRIKING A BALANCE
During the 1500s, Germany was going through a scientific renaissance and one of its most prominent figures was the great Swiss physician Paracelsus. His real name was Theophrastus Bombastus von Hohenheim and he was the first person to investigate medicine as a science rather than a superstition (although he did believe in gnomes—nobody’s perfect).
His most famous dictum is named the Paracelsus principle in his honor and it’s simple: “the dose makes the poison.” In other words, whether something is beneficial or harmful is all about the quantity.
Even something like cyanide is only harmful above a certain level. In fact, apple seeds contain amygdalin, which your body converts to cyanide, but you’d need to eat the seeds from about eighteen apples in order to get sick (assuming radioactive bananas don’t kill you first).
The metals in your body are the same. If you don’t have enough copper then your immune system can’t function, but if you get too much your eyes turn reddish-golden. Beautiful for sure, but you won’t appreciate it since you’ll be vomiting blood at the same time.
The element arsenic is famous for its use as a poison, but in small doses it can treat leukemia.11 It was also the central atom in Salvarsan, the world’s first wonder-drug and the main reason we don’t hear much from syphilis these days.12 Antimony can be administered as an anti-bacterial agent but too much starts killing the host, and a small amount of cerium can treat tuberculosis but too much gives you a heart attack.13
The Paracelsus principle is why your medication has a recommended dosage. Get the amount of chemical right and you save lives, get it wrong and you end them.
WHY ARE THINGS POISONOUS IN THE FIRST PLACE?
The honest-to-God truth is that we don’t know why some things are bad for you and others are good. Given the number of chemical compounds that exist, it would be impossible to catalog the effect of each one. We’ve only known about molecular bonding since the late 1920s so it’s no surprise that much of biology is still out of our reach. It’s been doing its thing for over three billion years so there’s no way we’ll have it figured out in a century.
Human
s are a delicate balance of reactions. If we alter one of them we can trigger a chain reaction and the final outcome can be unpredictable.
For example, if you get too much of the element tellurium in your body it causes horrendous breath and elemental silver will turn your skin blue, a condition known as argyria.14 Even nitroglycerine, which we met as the active ingredient in dynamite, is used to treat angina and nobody’s sure why it works.15
One of the few poisons the actions of which we do have a good understanding is cyanide. It works because cyanide molecules bond strongly to iron. If they happen to bond to the iron at the center of a molecule called cytochrome c oxidase, the iron can no longer be used and the whole thing shuts down.
This is bad news because cytochrome c oxidase is the molecule we need to extract energy from food. Switching it off means we essentially starve to death in a matter of minutes rather than weeks.
We also know that some elements, particularly heavy metals, are poisonous because they’re similar to elements your body needs and enzymes can accidentally incorporate them.
Zinc is needed for growth, and the element cadmium has a similar size so if you ingest it the body starts building enzymes with cadmium instead. Cadmium doesn’t have the right orbitals to interact with the chemicals in your body, however, and the result is that you suffer from cadmium poisoning. Your body stops growing.
Lead poisoning occurs because lead is a similar size to calcium, needed to manufacture red blood cells, so if your body absorbs too much lead you can’t make blood. Mercury is even worse because it’s the right size to fit through membranes surrounding your brain. Once it gets inside, it can affect your nervous system, not to mention your thought patterns.
