February 7 – National Periodic Table Day

nPostednon February 7, 2016

nNotnlong ago I wrote about Dmitri Mendeleev‘s Periodic Table ofnthe Elements. I linked to an interactive table, a video, some coolnPeriodic Table products, and of course the wonderful Periodic Tablensong.

nSo…whynis TODAY Periodic Table Day?

nAsnwith all scientists, Mendeleev came up with his contribution byn“standing on the shoulders” of past scientists who had madenearlier contributions. (One of the most respected scientists ever wasnSir Isaac Newton, and he once wrote, “If I have seen further it isnby standing on the shoulders of Giants.”) That’s one of the mostnmarvelous things about science – whatever works is kept, ideas thatnare disproven fall away, and we hone in little by little to a better,ntruer understanding of life, the universe, and everything.

nTodaynwe acknowledge one of the earlier scientists who noticed the patternnto the properties of elements. On this date in 1863, English chemistnJohn Newlands published one of the first table of elements. At thatntime, 63 elements were known; Newlands arranged the elements bynincreasing atomic weight and assigned them atomic numbers that showednthat order. He grouped them into 11 different groups and suggestednthe “Law of Octaves”: any one element has similar properties tonelements eight places before and behind it on his table.

nNewlandsnwas correct about there being patterns of properties, and he was ablento correctly predict an element that was eventually discovered andnnamed germanium. However, at the time he presented his idea, it wasnridiculed by many other chemists, and his lecture presenting the ideanwas not published.

nActually, Newlands arrangement of the elements was not as helpful to chemists and did not make as many accurate predictions as Mendeleev’s table, so in my opinion, Mendeleev deserves the credit that he receives. However, Newlandsndid have some great ideas, and he ended up fighting to receive some credit and recognition after Mendeleev’s table was published and praised!

nWhy…?

nYounare hopefully wondering why the chemical elements should follow anpattern of eight. n

nIt’snbecause electrons of atoms can only exist at certain energy levelsn(and therefore certain distances from the atom’s nucleus). And thenfirst several energy levels can hold up to two electrons (in the first shell) or up to eight electrons (in the next two shells). Checknout this video.

nAndnthe outermost electrons (which are called the valence electrons) arenthe ones that react with other elements. Check out this video.