Wednesday 7 February 2018

February 7th: Periodic table day

The periodic table is a way of listing the elements. It has been described by some as a "giant cheat sheet". Here are some facts about it you may not know.

  1. The periodic table was proposed by Russian chemist Dmitri Mendeleev in 1869. He came up with it when facing a publisher's deadline and needed a quick and easy way to represent all the elements thus far discovered - 63 of them. He was a fan of card games, and was inspired to write the name of each element on an index card and sorted them into columns and rows with similar properties.
  2. It still didn't look exactly like it does on modern day classroom walls - it was re-designed in 1923 by Horace Groves Deming for use as a hand out.
  3. Mendeleev wasn't the first person to try and come up with a visual representation of the elements. Several chemists had tried before, starting with Antoine Lavoisier in 1789. He published a list of 33 chemical elements, grouping them into gases, metals, nonmetals, and earths. What made Mendeleev's table popular was that he left blank spaces where an element had apparently not been discovered. He was able to work out the properties of the then theoretic elements that would fit in the spaces. When those elements were discovered later, he was proved right, as with gallium and germanium.
  4. Mendeleev's table didn't predict everything, though. Argon, Helium, neon, krypton, xenon, and radon, when they were discovered, didn't fit his system at all, so for several years, he denied they even existed. In 1902 he acknowledged he had not anticipated the existence of these elements—the noble gases—which now make up an entire group of the table.
  5. The rows in the periodic table are called periods (hence the name periodic table) and the columns are called groups. There are eight periods and usually 18 groups, although to be completely accurate the elements usually shown in a separate block at the bottom are sometimes incorporated into the main table so it has 32 columns. However, this doesn't fit so easily into a book, so is relatively uncommon.
  6. Elements are listed in the table by the structure of their atoms. From left to right and top to bottom, the elements are listed in the order of their atomic number, which is the number of protons in each atom.
  7. Mendeleev's table as modified by Deming hasn't been the final version ever - chemists and physicists continue to experiment with different ways of representing the elements. As well as variations in a rectangular format, there have been circles, cubes, cylinders, spirals, pyramids, spheres and triangles. Even before Mendeleev there had been three dimensional models.
  8. At time of writing, there are 118 elements in the table. Only the first 94 exist in nature; the rest have been synthesized in laboratories. The International Union of Pure Applied Chemistry, IUPAC, is responsible for issuing new versions of the table as new elements are discovered and named. The work of looking for new elements continues with scientists currently looking for an element 120. They don't know how far they can actually go in creating new elements. The higher the atomic number, in general, the more unstable they are and therefore the more difficult to make and study. There's a theory, though, that elements with higher numbers may start to become more stable. How far can we go? We don't know, but several scientists have hazarded guesses. Richard Feynman, for example, thought it would be impossible to get above atomic number 137, while others have suggested 128 or 155.
  9. Technetium was the first element to be made artificially. The most recent addition to the table is oganesson.
  10. A fun game people play sometimes is to spell out words or their name using chemical symbols in the table, for example "genius" would be GeNiUS (germanium nickel uranium sulphur). However, there is one letter of the alphabet which doesn't appear and makes it impossible for many of us - that letter is J.

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