by Tim James
The world’s spiciest pepper at the time of writing is the Dragon’s Breath chili, bred into existence by Welsh spice-master Mike Smith and possessing an SHU of over 2.4 million.2 That’s basically the same as pepper spray. This chili is so hot it would trigger anaphylactic shock if you ate it, but that’s nothing compared to the world’s spiciest chemical: resiniferatoxin.
Produced in the latex of Euphorbia resinifera plants (also called resin spurges), nobody has ever carried out taste trials with resiniferatoxin because it is acutely toxic and causes severe burns to the skin, meaning we have to calculate its SHU indirectly.
A study carried out by Arpad Szallasi in 1989 (on rats) found that resiniferatoxin was one thousand to ten thousand times better at binding to TRPV1 receptors than the chemical in chili peppers.3 Since we know chili peppers have an SHU of around 16 million, resiniferatoxin is going to score somewhere in the region of 16–160 billion SHU. That’s spicy enough to kill you.
There are many other chemicals that have record-breaking effects on our senses too. The sweetest chemical, so sickly it induces vomiting, is called lugduname, 230,000 times sweeter than table sugar.4
The darkest chemical, so black you can’t even see a torch shining on it, is called vantablack.5
And the worst-smelling chemical is a tie between propanthione and methanethiol, substances that have caused mass unconsciousness, spontaneous vomiting, and even death from smelling them at a distance.6
THE ELEMENT WAR
The first attempt at properly identifying elements was done by none other than Pythagoras himself, although it was a little bit weird. Most people know Pythagoras from the square-on-the-hypotenuse law they learned in school. What’s not usually mentioned is that Pythagoras was also probably the world’s first cult leader.
Not a great deal is known about the Pythagorean order because revealing their secrets would get you exiled, but we know they were forbidden from touching white chickens or eating beans.7 Pythagoras was murdered because an angry mob chased him to the edge of a bean field and, rather than entering it, he turned toward the crowd and chose a fatal beating.8
The only other thing we know about the Pythagoreans is that they considered numbers to be elements. Pythagoras and his cult worshipped numerical order, believing math to be the true face of reality. Their table of elements was simply a list of numbers going from one upward. Okay then.
Other people chose more tangible substances as their elemental matter. We met Heraclitus, who proposed fire as a candidate, in Chapter 1. Thales, who we met in Chapter 4, favored water because it took many forms, while the philosopher Anaximenes declared air to be the purest material, and so on.
It was a man named Empedocles who brought order to all the squabbling in the fifth century BCE. Rather than backing any of the other thinkers, he took the diplomatic approach and suggested that maybe everyone was right. Perhaps there wasn’t just one element but several.9 Empedocles’s periodic table would have looked like this:
This surprisingly simple solution ended the arguments and everyone was happy. Thales could keep his water, Anaximenes his air, Heraclitus his fire, and Pythagoras was dead in a bean field so nobody cared what he thought.
Nowadays, some people still think of these substances as being elemental but there is really no justification for this. They were chosen for peace-keeping politics rather than accurate knowledge, although sadly a lie can remain popular if people like it and it is easy.
THE TABLE MAKES ITS DEBUT
Once Antoine Lavoisier discovered that air was a nitrogen/oxygen mixture and water was a hydrogen-oxygen compound, scientists abandoned Empedocles’s four-element idea and began burning or dissolving everything they could lay their hands on to obtain the true elements.
By 1789, a lot of new ones had been discovered so Lavoisier gathered all the information and published a complete list, totaling thirty-three elements in all.10
He put them in four categories: gases, which were invisible but occupied space; metals, which were shiny and burned in oxygen; non-metals, which could be used to make acids; and earths, which didn’t fit the category of metallic or acid-making.
Lavoisier’s table was the first not to be based on guesswork or gut feeling and it looked like this:
The substances indicated with an asterisk were later discovered not to be elements but for a first attempt his table was pretty good.
Other chemists had their own methods of grouping things, of course. The German chemist Johann Döbereiner grouped elements into families of three based on how similarly they behaved. The metals lithium, sodium, and potassium behave identically, for instance. They react violently with water, tarnish in air, and can be sliced with a knife (if you’ve never had the joy of cutting a piece of lithium metal, it feels like ice cream straight from the freezer).
A similar observation worked for sulfur, selenium, and tellurium. All three were powdery solids that reacted with oxygen to produce strong-smelling compounds. Döbereiner called these groups triads, but there was no apparent reason for the patterns.11 The finished table of elements would have to somehow explain these mysteries.
A MUSICAL INTERLUDE
The most famous stab at a periodic table, before the one which actually worked, was a doomed attempt by the Englishman John Newlands in 1863.12 Methods had already been devised to measure the weights of atoms pioneered by Swedish chemist Jöns Berzelius (who also introduced the element symbols we use today)13 so Newlands obtained the data and wrote a list of the elements in order of ascending mass. As he did so, he discovered that the elements almost followed a cyclic pattern the way musical notes do.
In Western music theory, there are only seven principal notes. If you start at any particular tone and play up the scale you’ll discover that the eighth note is identical to the first, just a higher version. Note nine is a higher version of note two and so on. One complete set of notes is called an octave and the notes spiral up and up until the human ear can no longer catch them.
John Newlands applied the same logic to his table of elements, claiming there were seven categories that repeated over and over as we got to higher masses. The first seven elements made the first row, while the eighth element would be the first entry on row two, having similar properties to element 1 directly above it.
He called the seven columns of his table “families” and the eight rows “periods,” meaning something that repeats regularly. Thus, John Newlands introduced the idea of elements being “periodic.”14
The idea of periods turned out to have some truth to it, but his table had one minor flaw, which can sometimes prove inconvenient for a hypothesis: it was wrong.
At the time Newlands composed his table (pun very much intended), there were sixty-three elements known, which didn’t fit into an eight by seven grid. So rather than adding an extra column or abandoning the octaves idea, Newlands shoved a bunch of elements into the same grid squares.
The metallic element cobalt, for instance, having the audacity to exist, nudged later elements out of their correct families, which didn’t match the hypothesis. Newlands decided that cobalt and nickel were therefore the same element.
They aren’t. (Although, fun fact, both get their names from German sprites, Kobold and Nickel.)
Newlands knew these elements weren’t the same as each other but this kept his table neat, so best not to worry about it. He then had to do the same thing with awkward vanadium and again with lanthanum. In doing so, Newlands fudged the data to fit his idea. We have a word for that in science: cheating.
It would be like claiming there were three types of animal: cows, goldfish, and pigeons—then when someone shows you a tiger you decide it’s a cow really and put it in the same column.
Newlands also cherry-picked the elemental features. Cobalt is a lustrous metal with magnetic properties but his table aligned it with fluorine, chlorine, and hydrogen, all reactive gases. Newlands was happy to point out that chlorine, hydrogen, and fluorine belonged together but igno
red the fact that cobalt didn’t.
As a scientist, your job is to recognize when your hypothesis has failed. If nature says your idea is wrong then you get a new idea, you don’t tell nature what to do.
As a result, Newlands’s table was rejected by the scientific community of the day, although the story does have a happy ending. Every scientist has published a dodgy idea at some point, so scientists are a forgiving bunch who try not to hold grudges. If one idea turns out to be wrong, your others are still given a fair hearing. It’s useful to have that approach because, although Newlands’s octave hypothesis was wrong, his idea of periodic repetition turned out to be on the money. Elements do obey a cyclic pattern but a much more complicated one than he had assumed. He was, for this realization, awarded the Davy Medal for Chemistry by the Royal Society in 1887.
THE DREAMER
Dmitri Mendeleev was born in Siberia in 1834, the youngest of probably thirteen children (historians can’t agree on the number, but I’m sure his parents knew).
When his father went blind, Dmitri supported the family financially by tutoring science and, according to those who saw him in action, he was a fantastic communicator, full of passion and enthusiasm for both the subject and the art of explanation.
At the age of fifteen, his mother decided he needed a higher education and took him across Russia on foot, applying to as many universities as they could along the way. The expedition took close to a year and sadly her health worsened as the months drew on. She died when they reached St. Petersburg, but lived long enough to see her son get admitted to study joint-honors in chemistry and teaching at St. Petersburg State University.
She would have been proud of his accomplishments, as he soon became one of the most outstanding chemists in Russia, with a reputation for writing huge textbooks from memory in a matter of months, and helping establish the country’s first oil refinery in Tutayevsky.
He was also an imposing character, who shaved his beard once a year and had fiery clashes with other students and professors. His greatest contribution to science though was creating the very first periodic table that actually worked.15
A few days prior to his breakthrough, Mendeleev made a deck of playing cards with elements instead of suits on their faces. He invented a version of solitaire based on chemical properties and hoped it would help him discover a deep pattern about their organization.
According to his friend Alexander Inostrancev, Mendeleev had been awake for three days and nights playing the game when he finally collapsed from exhaustion on the afternoon of February 17, 1869.
Mendeleev fell asleep surrounded by his playing cards and had the most vivid dream of his life. In the dream, he saw the playing cards dancing before his eyes and dropping into place perfectly, revealing the pattern for which he had been searching.16 The elements did follow a cycle, but nobody had figured it out because there were still elements missing!
Up until then, people had been discovering elements at random and grouping them based on color, reactivity, conductivity, thermal properties, and anything else you could name.
Mendeleev realized that the elements were arranged in a sequence of increasing mass but that some were still hidden inside rocks. The elements that seemed to be in the wrong place weren’t: they were just next to elements that were unknown to chemists of the day.
Element 32 hadn’t been isolated yet, nor had 61 or 72. If we assumed Mendeleev’s law of increasing integers worked, we should find elements that matched those values and, sure enough, germanium, promethium, and hafnium were eventually identified and slotted into their respective gaps.
THIS WAY MADNESS LIES
By 1932, we knew that elements were made of atoms, themselves made from protons, neutrons, and electrons. But if every atom was made of the same three particles, why were they so different from each other?
Take element 35, bromine. It’s a thick, mauve liquid that sets fire to metal and corrodes human skin. The next element is number 36, krypton. That’s a harmless, invisible gas with no odor or reactivity. The only difference is that krypton has one extra proton/electron than bromine, so why don’t they behave similarly?
And what can we make of Döbereiner’s triads? Elements 29, 47, and 79 are copper, silver, and gold—all malleable metals with a lustrous finish. Why do those three numbers in particular end up with the same properties?
Why is element 4 a shiny solid while element 5 is a brown powder? Why is element 9 one of the most reactive known to man but element 10 one of the least? Why do elements 11 to 14 conduct electricity while elements 15 to 18 do not?
Any attempt to find order resulted in failure and a hypothesis has to account for all evidence, not just a convenient portion of it. If we couldn’t use the proton/neutron/electron model to account for the differences in behavior then we would have to abandon it.
The only conceivable explanation was that although each atom was made of the same three particles, they were somehow arranged differently in space. Democritus had already suggested that atoms came in different shapes (fire atoms were spherical, which allowed them to move easily, while “bitterness” atoms were sharp and jagged). Could he have been on the right track?
The answer finally came when physicists discovered one of the most important theories in modern science, the one that gave the periodic table its final form. Quantum mechanics.
CHAPTER SIX
Quantum Mechanics Saves the Day
QUANTUM CRASH COURSE
Quantum mechanics is infamous. Everyone has heard about it and its reputation for being weird (a reputation that is well deserved, by the way). However, in recent years, some of the vocabulary has been hijacked by spiritualists to mean all sorts of unrelated things, which sadly confuses the issue. Don’t misunderstand me; there’s nothing wrong with talking about spirituality but repurposing words from quantum mechanics to mean something else is unhelpful. So we’ll tread carefully.
The first thing to say is that quantum mechanics is not one idea but a sophisticated collection of theories that explain the world at its smallest level. The behavior of electrons, the nucleus, light, and their interactions are all explained by quantum mechanics so it is of great importance to chemistry.
Covering it in detail would take a separate book entirely so we’ll limit the discussion to the part, developed by Austrian physicist Erwin Schrödinger, that helped build the periodic table.
Schrödinger caused a lot of discomfort during his life and was politely asked to leave a number of universities and institutions. This wasn’t because of his academic achievements, which were outstanding. It was because he lived in a three-way relationship with his wife Annemarie and their girlfriend Hilde. He also wore a lot of bow ties. Scandalous.
Schrödinger’s most important contribution to science is called the Schrödinger wave equation. It’s the equation that tamed the periodic table and explains why elements behave the way they do. It looks like this:
I know equations can sometimes put people off but this one is vital to the story, so we can’t just brush it under a rug. I’ve included a short explanation of what it means in Appendix III if you’re feeling adventurous but don’t worry, we can still understand what the equation does without having to go into any mathematical detail.
Nobody is sure how Schrödinger came up with his equation because there are no clear records of him deriving it. Some claim he simply woke up one morning, went downstairs, and wrote it based on gut feeling. It was only later that it was tested and proven correct.
What the equation does is tell us where electrons are likely to be as they zip about the nucleus. You start by taking the electron’s properties (things like its mass, velocity, etc.) and then figure out how much attraction there is from the protons of whichever atom you want to describe.
By solving the equation for a given atom we can map out a three-dimensional region of where electrons are going to be and what patterns they will trace out in space.
When we do this, we find that el
ectrons don’t move in circular orbits at all. They surround the nucleus in regions that come in a variety of shapes, the same way animals inhabit different-shaped enclosures at a zoo. We call these regions “orbitals” or sometimes when we’re being lazy, “electron clouds.”
Some electrons hang out in spherical orbitals while others occupy a dumbbell-shaped region protruding from the top and bottom of the atom. Each orbital can hold up to two electrons, so the more electrons you have on your atom the more orbitals end up being used and the more extravagant your atomic shape becomes.
The reason certain orbital shapes arise is because electron movements are sort of wavy. They don’t move in simple lines like marbles but seem to ripple as they travel from one point to another. Since ripples can only come in certain shapes (you can’t have half a wave, for example) so do the electron orbitals.
A boron atom, which has five electrons, will distribute them into orbitals shaped like the diagram on the left on page 65. Carbon, however, has six electrons so a new orbital shape gets introduced and the atom looks like the diagram on the right.
The fact that different atoms come in different shapes explains why they have difficult chemical behaviors. They stack together differently, bond at different angles, fit into different spaces, and so on.
Solving the Schrödinger equation for a particular element explains why it can be different to the element next door. Just because they have a similar number of electrons doesn’t mean they will have the same shape. It also answers the question every student asks when they see the periodic table for the first time.
WHY IS IT THAT SHAPE?
