“Water.

Earth. Fire.

Air.” Aristotle may  not have had a poster of the periodic table on his bedroom wall growing up. But he sure did have an idea about  what everything on Earth was made of. That idea was very, very wrong, of course, even if it did help spawn a  beloved television series.

But over the following millennia, scientists slowly worked things out. By the time Dmitri Mendeleev published his  original version of the periodic table, in 1869, there were 63  elements that scientists knew made all the matter we can  see, touch, and so forth. Part of that was thanks to  advances in scientific theory, like Dalton’s concept of the atom.

Part of it was thanks to advances in  scientific methods and technology. But the path from 63 to the current  118 elements was not straightforward. In fact, there are many times scientists  thought they had discovered a new element, but didn’t.

So many in fact, you could make  a SciShow List Show about it… [intro jingle] Here’s a lie that your teacher might  have told you when you were young: “Sunlight is made up of all  the colours of the rainbow.” And by “lie ”, I mean it’s so close to true almost no one is going to call that teacher out. Except for when it actually matters. Like right now.

In the early 1800s, the German glassmaker Joseph von Fraunhofer split sunlight up into its constituent colors using a device he invented called a spectroscope. And he found 574 dark lines  in the otherwise full rainbow. In other words, a bunch of colors were missing.

These lines turned out to be super important for chemistry, physics, astronomy, and optics. Fraunhofer’s discovery was,  and remains, a pretty big deal. He was the first to document  these spectral absorption lines, caused by atoms absorbing  specific amounts of energy from light that’s passing through.

Because when you’re dealing with light,  energy corresponds to wavelength… that is, color. Then the 1860s, some other German scientists… including Robert Wilhelm  Bunsen of “bunsen burner” fame… found that absorption lines  had not-at-all-evil twins called spectral emission lines that show up when you split up  the light coming from an element when it’s burning. Both emission and absorption lines are the result of an atom’s electrons  jumping between energy levels.

When it’s emission, the electron  is emitting that energy, so it’s dropping down some number of levels. When it’s absorption, it’s the opposite. The exact amount of energy, and therefore the exact color of the light, depends on several factors, including  how many electrons are involved, and which levels they’re jumping between.

Both of these lines act  like chemical fingerprints, because each atom has a unique  set of lines that they produce. So element hunters started using spectroscopes to split light from all sorts of places to find unique new fingerprints,  and therefore elements. Remember that this is right around when Mendeleev is coming up with his periodic table.

He’s arranged the known elements  according to atomic weight, but he realised that there are  repeating patterns of properties. When he mapped it all out, there were actually gaps where  unknown elements might be. And that’s where people started.

During a total solar eclipse  in 1869, two Americans named William Harkness and Charles Young  split the light coming from the Sun’s corona… the only part you can see  during a total solar eclipse… and identified a green line  in the emission spectrum that didn’t correspond to any known element. In other words, they claimed  they’d discovered a new element. They dubbed it “coronium”.

And assuming their discovery was legit,  they’d find themselves in excellent company. Helium was discovered in the Sun’s  spectrum just one year earlier. And earlier that decade, both rubidium and cesium were discovered using spectroscopy… although by looking at more down-to-Earth sources.

So it was reasonable that there might  be another new element in the Sun. But coronium always bugged scientists because it couldn’t be isolated and  studied for its other properties. Eventually, in 1940…that’s a whopping  71 years after its initial discovery… two scientists named Grotrian  and Edlén found the true culprit.

It wasn’t a new element that was  creating this weird green spectral line. It was boring old iron. Or rather, iron that had gotten  so hot, it was no longer boring.

See, not all iron atoms will emit  the exact same spectral lines. Nor will the atoms of any element. A spectrum also depends on  how much an atom is ionized… how many electrons it has compared to  the number of protons in its nucleus.

On Earth, iron ions tend to come with  either a plus 2 or plus 3 charge, meaning it’s lost two or three of its electrons. To knock off more and more electrons,  you need more and more energy, so it’s harder and harder to do. Enter, the Sun’s corona, where temperatures  are in the millions of degrees, and iron can be ionized 13 times over.

The resulting spectral lines are so shifted,  they become utterly unrecognisable as iron. So that was one problem solved. But it took so long, there was time for  astronomers to make yet a second mistake before they realized they even had one… Around the year 1864, William Huggins  used his telescope and spectrograph to observe the Cat’s Eye

Nebula: a cloud of  stellar debris surrounding a white dwarf… the remnants of a star too small  to end its life with a supernova. Astronomers call these things planetary nebulas, despite having nothing to do with planets. But we don’t have time to get  into the history of that mistake. Like Harkness and Young before him, Huggins also observed an unusual green line that didn’t correspond to any known element… not even coronium.

So he concluded that some portion of the nebula must be made of yet another element. Proposed names included Nebulum and  Nebulium, and their Greek counterparts Nephium and Nephelium. Nebulium seems to be the one that stuck.

Or at least it did until 1927, when  scientists figured out that this green line was actually created by  doubly-ionized oxygen atoms. The reason Huggins and others  didn’t realize this sooner is because the density of a  planetary nebula is crazy low. There’s a few hundred particles in  every cubic centimetre of a nebula, compared to the ten quintillion  particles per cubic centimetre in the air you’re breathing right now.

The only places you find on Earth with densities like this are in the ultra-high-vacuum  areas of the Large Hadron Collider meant to mimic interstellar space. Because of this, atoms with excited electrons don’t have the opportunity  to lose that extra energy through collisions with other atoms, like they would on Earth. Instead, all they can do is a big jump back  to their lowest, “ground” energy level, which makes for a really weird spectral line.

In fact, astronomers still call spectral  signatures like this forbidden lines, because they break normal Earth rules. But forbidden or not, the lines  weren’t caused by a new element. They were a boring known element doing something decidedly un-boring and un-known.

So no more Nebulium. Despite setbacks like these, the periodic table really was filling  out as we moved into the 20th century. The race was on to plug those last few holes where scientists knew an element needed to go.

One of those holes was almost smack dab  in the middle of the table: element 43. We now know it as technetium, but many people claimed to  discover it through the decades, and tried to name it something else… such as davyum, lucium, and nipponium. But you won’t find any of those  names on your bedroom poster.

In 1925, Otto Berg, Walter Noddack, and Ida Tacke… who married Walter and became  Ida Noddack the following year… claimed they’d discovered both elements 43 and 75. They named them Masurium  and Rhenium, respectively. Because 43 and 75 appear in  the same column as manganese, many element hunters thought they’d  share similar properties as manganese, and might also occur in the same kinds of ores.

But Walter and Ida thought  they might actually resemble their horizontal neighbors on the periodic table, so they investigated ores  containing those elements, instead. After melting samples down and subjecting  them to a suite of chemical reactions, to extract and isolate any hidden  elements they passed the results to Otto. Otto then used his expertise in x-ray spectroscopy to confirm there was anything  to actually discover.

This kind of spectroscopy was  only a few years old at the time. It required shooting electrons at an element so that it absorbed a bunch of energy. And when its atoms released that energy as x-rays, the wavelengths of those rays would be  related to the element’s atomic number.

The team’s evidence for rhenium was accepted by the International Union of Pure &  Applied Chemistry, or IUPAC for short… the people who get to decide when an  element officially gets discovered, and what its name gets to be. But the evidence for Masurium wasn’t  convincing or reproducible enough for them. In fact, there has since been  quite a lot of scientific argument about whether the Noddacks and  Berg actually did find element 43.

But in 1937, credit for the discovery ultimately  went to Emilio Segrè and Carlo Perrier. Their research started with a piece of scrap, irradiated molybdenum from Ernest  Lawrence’s lab at Berkeley. So props to that person for being  willing to ship the thing over to Sicily.

Lawrence eventually got an  element named after him, so don’t feel too bad about him missing  out on this particular discovery. As element 42, molybdenum is just  one proton shy of its neighbour 43. And over the course of  several months of experiments, the Berkeley plate had been bombarded  by oodles of deuterium atoms.

Deuterium is a heavier version of hydrogen, with the standard one proton but also one neutron. Given the right conditions, it can fuse with molybdenum to create element 43. And from this plate, the Italians  had isolated enough atoms to convince the chemistry authorities.

The name they chose was technetium,  from the greek word for “artificial”, because thanks to all that deuterium bombardment, it was the first element produced  by humans rather than nature. But of course, it was far from the last… …in history, at least. It’s definitely  the last before our ad break.

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Thank you to Brilliant for  supporting this SciShow video. One year after Berg, Noddack, and Tacke  claimed to fill the hole for element 43, two teams fought for the  rights to name element 61. The team based in Florence, Italy  wanted to name it Florencium.

The team based in Chicago, Illinois  wanted to name it illinium. Both claimed to have discovered the  element based on faint spectral lines they measured in the light that was  passed through samples of the element. But nobody else could replicate their experiments, or isolate a chunk of the element.

It turns out, there’s a pretty good reason  for that: element 61 is so radioactive, even the most stable version  has a half-life of 17.7 years. If you were given a 1 kilogram chunk  of it on the day you were born, you’d only have 500 grams  left by your 18th birthday, 250 grams by your 36th, and so on. The Earth, of course, is way older than you.

A one million year old rock that started  with a kilo of element 61 inside it won’t have a single atom left. It’s  basically impossible to find in nature. So what had the Italians and Americans detected?

Probably some lines coming from  contaminants in their samples. By which I mean elements  they already knew existed. The real element 61 would stay hidden  until nuclear reactors were built.

With access to that technology, scientists could create radioactive  material with an even higher element number, and when that stuff inevitably decayed, enough could turn into 61 to get detected. In 1945, a group from the Oak Ridge  National Laboratory in Tennessee started looking at the spent  fuel from their nuclear reactor, which had been producing  plutonium for the atomic bomb. They separated out the different elements using  a technique called ion-exchange chromatography, which sorts and filters things based on  their charge, size, and chemical properties.

This allowed them to find enough element  61 to be sure of their discovery. They named it Promethium, after the titan from Greek mythology  who introduced humans to fire. And while nobody wound up chained to a  rock with an eagle pecking out their liver, they all probably experienced some  negative side effects from their research, given the constant threat of  radiation poisoning and all.

For our last two elements, we’re  gonna tackle them together. Because we’re dealing with the same guy who thought he discovered both  of them around the same time. Take a look at your nearest periodic  table, bedroom poster or otherwise.

You’ll notice that basically  all of the heavy elements… past lead or so…are 100% radioactive. And once you pass uranium, the half-lives  are too short for you to find them in a random rock or whatever. While this tells scientists something  interesting about how atoms are organized, it also poses a problem for anyone  trying to find and study these elements.

So like technetium and  promethium, they need to be made. But let’s step back a moment: one of the ways a radioactive atom tries to  become more stable is known as beta decay. A neutron splits into three new particles:  a proton, an electron, and an antineutrino.

Only the proton stays in the nucleus; the  other two are ejected from the atom entirely, so we don’t care about them right now. But since it’s the number of protons  that determines what element the atom is, you’ve now got yourself a new element. And in the 1930s, scientists figured that we could harness this power  to create new elements at will.

At that point in history, uranium was  the last element on the periodic table. But if you took a lump of uranium  and bombarded it with free neutrons, some of the uranium atoms  would absorb those neutrons and become even more unstable  than they already were. Then, those atoms would undergo beta decay, turning neutrons into protons.

And voilà, you’ve got yourself a  new element with a number above 92. This was the science behind Enrico Fermi’s 1934  claim that he’d discovered elements 93 and 94. He and his collaborators looked  at how quickly the uranium and   thorium they’d bombarded with neutrons decayed.

The curves they charted didn’t  look like those of uranium,   thorium, or any other element down to radon. So they concluded they had found  something new and heavier than Uranium. Fermi named 93 Ausonium, after the  Greek name for Italy, and 94 Hesperium, after yet another name for Italy  found in some Latin poetry.

We get it, the guy loved Italy. But in 1934, no one knew about a pretty  important phenomenon in particle physics: nuclear fission. An atom can also get apart  by shooting neutrons at it.

In other words, Fermi may not  have made elements in the 90s, he may have made much lighter elements  that everyone already knew about. But because he assumed atomic numbers could  only change one or two protons at a time, he only looked in the region of the  periodic table right around Uranium. You can probably guess what  later experiments revealed.

Yep, Fermi had not, in fact,  created elements 93 and 94. He had made a bunch of barium. And you know who was the first person  to figure all this fission mischief out?

Ida Noddack, the almost-discoverer of element 43. Noddack wasn’t the only  critic of Fermi’s “discovery,” but that didn’t stop the Nobel Prize committee from awarding him the Nobel Prize  in Physics in 1938 for, quote, “his demonstrations of the existence  of new radioactive elements produced by neutron irradiation.” By the time Fermi gave his Nobel Lecture, there was so much evidence he might be wrong, he added a footnote admitting his mistake. A couple years later, in 1940, Americans found the real 93 and  94 using a different method.

Instead of using neutrons, they shot their uranium with  helium nuclei to make element 94, which then decayed in a  different way to create 93. 93 was named Neptunium,  and 94 was named Plutonium, after the planets beyond Uranus. Fermi, meanwhile, did not  have to give back his Nobel. And he was good enough at  nuclear and particle physics that the scientists who discovered element 100 chose to name it Fermium.

There’s also Fermilab, the Fermi Paradox, an entire class of subatomic  particles called fermions… In terms of legacy, he’s doing alright. So if you’re out there waiting impatiently for  the next major update to the periodic table… element 119 or otherwise… I recommend passing the time by telling  your friends, distant relatives, and internet strangers about the guy who won a Nobel for discovering two elements that don’t exist. Or any of the stories we’ve covered today. [ OUTRO ]