Thursday, March 29, 2012

10 Things You Didn't Know About...

>The Periodic Table<

... *1 You may remember the Periodic Table of the Elements as a dreary chart on your classroom wall. If so, you never guessed its real purpose: It’s a giant cheat sheet.

*2 The table has served chemistry students since 1869, when it was created by Dmitry Mendeleyev , a cranky professor at the University of St. Petersburg.

*3 With a publisher’s deadline looming, Mendeleyev didn’t have time to describe all 63 then-known elements. So he turned to a data set of atomic weights meticulously gathered by others.

*4 To determine those weights, scientists had passed currents through various solutions to break them up into their constituent atoms. Responding to a battery’s polarity, the atoms of one element would go thisaway, the atoms of another thataway. The atoms were collected in separate containers and then weighed.

*5 From this process, chemists determined relative weights—which were all Mendeleyev needed to establish a useful ranking.

*6 Fond of card games, he wrote the weight for each element on a separate index card and sorted them as in solitaire. Elements with similar properties formed a “suit” thathe placed in columns ordered by ascending atomic weight.

*7 Now he had a new Periodic Law (“Elements arranged according to the valueof their atomic weights present a clear periodicity of properties”) that described one pattern for all 63 elements.

*8 Where Mendeleyev’s table had blank spaces, he correctly predicted the weights and chemical behaviors of some missing elements—gallium, scandium, and germanium.

*9 But when argon was discovered in 1894, it didn’t fit into any of Mendeleyev’s columns, so he denied its existence—as he did for helium, neon, krypton, xenon, and radon.

*10 In 1902 he acknowledged he had not anticipated the existence of these overlooked, incredibly unreactive elements—the noble gases —which now constitute the entire eighth group of the table

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