What links cutting open rocks, fireworks, looking directly into the sun and smashing atoms together very, very fast. From the title of this series, you may have guessed. Good for you. If you recall last post, our extremely Russian friend Dmitri Mendeleev had just cracked the Periodic Table – uniting all of chemistry in a quest to complete it. The year when the Periodic Table was adopted by modern science was 1886 – the year when the last of Mendeleev’s predicted elements was actually discovered. Eka-silicon was now called germanium, and the quest was on. Before we can start on our search for the remaining 60-odd elements, there’s something I’m going to explain about the elements.
They are ordered into 10 groups : Alkali Metals, Alkali Earth Metals, Transition Metals, Lanthanides, Actinides, Poor Metals (or Post-Transition Metals), Metalloids, Non-Metals, Halogens and Noble Gases. In other words – the explodey ones, the burny ones, the shiny ones, the quite radioactive ones, the really radioactive ones, the not-so-shiny ones, the even-less-shiny-ones, the important ones, the poisonous ones and the boring ones.
If there are any chemists reading this and you are currently throwing up on your keyboard, I apologise. While I like being technical, I try to avoid overuse of jargon that might confuse the general population. So if you want to, chemists, you can print out this, Sharpie out the nicknames and stick it back onto the screen. If it makes you happier. And less likely to flame me.
Anyway, back to the list. Some of those groups are defined by a specific electron structure (to be explained in 2 weeks), and some of them are just because they react the same. Which is probably also down to electron structure, but I’m not even going to pretend to understand why. When Mendeleev first designed his Periodic Table, three of those groups hadn’t even been discovered.
The Lanthanides, Actinides and Noble Gases weren’t there to be fit in. So let’s start there. 1895- Helium. This was the first of the Noble Gases to be discovered, which makes sense – it’s the second most abundant element in the universe. It also mostly exists at the centre of stars, so it’s hardly lying around waiting to be found. The way it was found heralded in a new scientific technique that’s still in use today – spectral lines. Or, looking at the colour stuff makes when you set fire to it.
Spectral lines take advantage of the idea that different elements burn at different colours – and that they also block certain colours when you shoot white light through them. For example, when you burn rubidium, you get a pretty red colour. Rubidium is actually named after this – it burns ‘ruby red’, hence rubidium. But if you use a spectral-line-ometer (there’s probably a technical name for that) you can see exactly what colour it is. It’s those two red lines (in the emission spectrum) that give rubidium it’s pretty colour. Anyway, that’s how helium (and thallium and cerium) were discovered. Helium was literally discovered when someone looked at the sun during a solar eclipse, and saw some weird-looking spectral lines.
That’s the root of the word helium – helios is Greek for ‘the sun’. Helium is interesting, because it was the first noble gas to be discovered. Noble gases are the ones that react with very, very little – they are too ‘noble’ for these sort of things.
1902: Polonium This was one of the first radioactive elements discovered (uranium and thorium were found earlier, because they occur naturally) , and is one of the worst ones. You might know it from the ex-KGB agent who was killed when someone put some polonium-210 in his tea. It was discovered by Marie Curie, who went on to discover a bunch of other radioactive chemicals. And then died of leukemia, because radiation isn’t very good for you. Uranium, thorium, polonium and radium were all found from uraninite (a form of uranium ore). Without really noticing, we’ve added two more groups – the lanthaides and actinides. The first of each of these groups (lanthanum and actinium) were discovered in 1838 and 1899. These groups are the two rows that sit around at the bottom of the periodic table. The reason they go there is because they actually sit right at the start of the transition metals block. So if you were to actually insert them there, the periodic table would look like this. Which is ugly as hell. So most posters/websites show some variation on this. You can see the asterisks – they show that the whole block should actually be inserted into that slot.
1940-Astatine This is big news here. This is (sort of) the last element. It’s the 92nd element to be discovered, completing the entire natural periodic table. It had only taken 54 years for Mendeleev’s dream to complete itself, as a victory of modern science. It doesn’t matter the astatine is a really, really nasty element. Any lump of it big enough to see with the naked eye will instantly vaporize itself with the heat generated by the immense amount of radiation it gives off. But that doesn’t matter, because the Periodic Table had been completed. There were no more elements left to discover.
1940-Neptunium I lied. Astatine was the last natural element to be discovered, but it wasn’t the last. Not by a long way. For the 1940s were the age when nuclear physics was taking its first steps. All over America, scientists were putting uranium in boxes and using it to generate phenomenal amounts of power. And also new elements. When you put things in a nuclear reactor, lots of weird things happen. Atoms are ripped apart, bits of atoms go flying about everywhere and things mash together. I’ll explain more about nuclear fission (what is happening here) in another post. So I’ll use an analogy.
Imagine all atoms as clusters of balls made of Blu-Tack. In nuclear fission, you split these clusters apart and release lots and lots and lots of energy. And the cluster breaks into all the little Blu-Tack balls and they fly everywhere. And because the cluster is part of a fuel rod made of millions of clusters, most of those little balls go and hit other clusters. Sometimes they trigger another cluster to split -which is a chain reaction. And sometimes they mush into the other cluster, stick to the side and make a new, bigger cluster. I’ll talk more about what makes different atoms different next post, but it basically depends on one number – how many protons the atom has. If you increase the number of protons, you have a new and different atom. This is what happened in the Berkeley Radiation Lab in California, when some scientists were flinging bits of atoms at other atoms for
fun scientific reasons. They created neptunium and plutonium by hitting uranium with hydrogen, heralding in a new type of elements.
Transuranic elements are elements that sit at the far end of the Periodic Table. They don’t exist in nature – they are so big that they are unstable, and will always emit some form of ionizing radiation and eventually decay into something less nasty. You can find them past uranium – they are trans-uranic, beyond uranium.
This is the frontier we are currently chipping away at, since the official discovery of…
2006. Livermorium This is the furthest frontier of elemental chemistry. It’s an element that is created in very special labs, by bombarding curium atoms with calcium. It’s the single most radioactive substance ever created. Also, no-one has ever seen it. This is the problem with these new-fangled elements. As they get bigger and bigger, they decay faster and faster. Neptunium’s longest-lived isotope has a half life of 396 days (the half life is the time it takes for half of the atoms in any block of the element to decay into something else). By comparison, the longest-lived isotope of livermorium lasts about 0.061 seconds if you are lucky. It is so big that it decays faster than it can be detected. That’s why we have elements with names like ununoctium. These elements live and die so fast, it’s not enough for one person to find them. They need to be verified by several teams at different labs, to prove the new element isn’t an anomaly. The half-life of the only ununoctium sample ever created was 0.000081 seconds. The computer needs to be fast. And that’s how we got from Mendeleev’s 56 elements to the current 118. One block at a time.
Next Time: We’re going to take a little journey. A journey to the centre of the atom.