By John Emsley
I am sometimes asked the question: how many elements are there? I reply that there are several answers to that question. Should it include only those we know about? Then the answer is probably around 120 and I say ‘probably’ because some have been claimed but not confirmed. There are definitely 114 elements, although that includes some very transient ones. The latest additions are flerovium (element 114, previously called un-un-quadium, i.e. 1-1-4) and moscovium (element 116, previously called un-un-hexium, i.e. 1-1-6) their existence having been officially confirmed by the International Union of Pure and Applied Chemists in 2011. None of their atoms exist on Earth because no sooner have they been made than they disintegrate. (Elements 113 and 115 are still under investigation.)
Last year I had to vet a script for a television programme in which it was said there are 92 elements, that being the number of elements up to uranium, once regarded as the upper limit of what was to be found on Earth. However, I knew that element 43 (technetium) is too radioactive to occur naturally, and that astatine (element 85), francium (element 87), and actinium (89) have only a fleeting existence, formed as they are from the radioactive decay of heavier elements like uranium. The other radioactive elements polonium (84), radium (88), and protactinium (91) have half-lives long enough for chemists to have separated them from uranium ores. Madame Curie extracted radium and polonium from uranium ores back in the 1890s, and these elements are present in milligram quantities. Radon (86) is also present and this gas leaks from uranium ores, but it too has a short half-life, although long enough to pose a threat to health if it seeps into and collects in cellars and basements.
Eventually it was decided to leave the answer as 92 because there are atoms of all elements somewhere in the world, although on that basis I could have argued for 93 because there are even a few atoms of the radioactive element, neptunium, around.
What might the upper limit of atomic number be? I suspect it is around 128 but in the new edition of Nature’s Building Blocks I only go up to 127 because the attempts to make atoms of this element, have been unsuccessful. Even element 126 has yet to be made.
Of course there are lots of fascinating facts about the elements apart from their discovery. In Nature’s Building Blocks I have various topics for every element, such as Human element, Food element, Medical element, Dangerous element, Historical element, Economic element, Environmental element, and even Element of Surprise. This last category is reserved for information which you would not expect. For example, under uranium I was able to report that some ancient Roman mosaics were coloured with a uranium oxide pigment.
Although as a chemist, my tendency is to list the elements according to their atomic number, which is the number of positively charged protons in the nucleus, starting with hydrogen (1), then helium (2), lithium (3) and so on. However, for the general reader an alphabetical order seemed more user-friendly and this is how they are arranged in the book. Back in 2001 when I finished the 1st edition of Nature’s Building Blocks I assumed that its 538 pages contained all the information that the general reader might ever need. How wrong I was. I continued to collect data on the elements and I was surprised just how much extra material I’d amassed in the 10 years since the first edition.
Particularly noticeable has been the development of the 15 lanthanoid elements which are now of global significance, being a vital part of wind generators, mobile phones, iPads, flat screens, and hospital equipment. So important have these elements become that the search is on for new sources, because all those current available come from mines in China. There is a large deposit in the USA but that ceased production around 10 years ago because they could not compete with the Chinese producers. Now that prices have risen, that mine is being opened up again, and might soon be joined by other producers because a large deposit of lanthanoid ore has been found in Greenland.
It’s not only these elements which have seen new uses. For example gold, which is so unreactive that you might assume there would be little new to report, has taken on an unexpected role especially as a catalyst, and gold nanoparticles are showing a very different chemistry compared to gold in its normal unreactive state.
In the 1st edition I had something curious to say about all the elements but one, and that was thulium (element 69) which is one of the lanthanoids. Ten years ago there appeared to be no use for it, but now there are interesting facts to report about this rare earth element. It has a key role in the lighting used in film studios, and in personal radiation detectors.
John Emsley won the Science Book prize in 1995 for his Consumer’s Good Chemical Guide, and followed this with a series of popular science books: Molecules at an Exhibition, Was it Something You Ate? (co-authored with P. Fell), and The Shocking History of Phosphorus, all of which have been translated into many other languages. After 20 years as a researcher and lecturer in chemistry at London University, he became a freelance writer, as well as Science Writer in Residence, first at Imperial College London and then at Cambridge University. In 2003 he was awarded the German Chemical Society’s Writer’s Award. OUP has recently published a new edition of his book Nature’s Building Blocks: An A-Z Guide to the Elements.