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spelling arose b cause of some uncharacteristic indecisiveness ondavys part。 when he first isolated the element in 1808； he called it alumium。 for son reason he thought better ofthat and changed it to aluminum four years later。 americans dutifully adopted the new term； but mai britishusers disliked aluminum； pointing out that it disrupted the …ium pattern established by sodium； calcium； andstrontium； so they added a vowel and syllable。
2the principle led to the much later adoption of avogadros number； a basic unit of measure in chemistry； whichwas named for avogadro long after his death。 it is the number of molecules found in 2。016 grams of hydrogengas （or an equal volume of any other gas）。 its value is placed at 6。0221367 x 1023； which is an enormously largenumber。 chemistry students have long amused themselves by puting just how large a number it is； so i canreport that it is equivalent to the number of popcorn kernels needed to cover the united states to a depth of ninemiles； or cupfuls of water in the pacific ocean； or soft drink cans that would； evenly stacked； cover the earth to adepth of 200 miles。 an equivalent number of american pennies would be enough to make every person on eartha dollar trillionaire。 it is a big number。
driven in large part by developments in chemistry； and yet as an organized science chemistrybarely existed for decades。
the chemical society of london was not founded until 1841 and didn鈥檛 begin to produce aregular journal until 1848； by which time most learned societies in britain鈥攇eological；geographical； zoological； horticultural； and linnaean （for naturalists and botanists）鈥攚ere atleast twenty years old and often much more。 the rival institute of chemistry didn鈥檛 e intobeing until 1877； a year after the founding of the american chemical society。 becausechemistry was so slow to get organized； news of avogadro鈥檚 important breakthrough of 1811didn鈥檛 begin to bee general until the first international chemistry congress； in karlsruhe；in 1860。
because chemists for so long worked in isolation； conventions were slow to emerge。 untilwell into the second half of the century； the formula h2o2might mean water to one chemistbut hydrogen peroxide to another。 c2h4could signify ethylene or marsh gas。 there was hardlya molecule that was uniformly represented everywhere。
chemists also used a bewildering variety of symbols and abbreviations； often self…invented。
sweden鈥檚 j。 j。 berzelius brought a much…needed measure of order to matters by decreeing thatthe elements be abbreviated on the basis of their greek or latin names； which is why theabbreviation for iron is fe （from the latin ferrum ） and that for silver is ag （from the latinargentum ）。 that so many of the other abbreviations accord with their english names （n fornitrogen； o for oxygen； h for hydrogen； and so on） reflects english鈥檚 latinate nature； not itsexalted status。 to indicate the number of atoms in a molecule； berzelius employed asuperscript notation； as in h2o。 later； for no special reason； the fashion became to render thenumber as subscript： h2o。
despite the occasional tidyings…up； chemistry by the second half of the nineteenth centurywas in something of a mess； which is why everybody was so pleased by the rise toprominence in 1869 of an odd and crazed…looking professor at the university of st。 petersburgnamed dmitri ivanovich mendeleyev。
mendeleyev （also sometimes spelled mendeleev or mendel茅ef） was born in 1834 attobolsk； in the far west of siberia； into a well…educated； reasonably prosperous； and verylarge family鈥攕o large； in fact； that history has lost track of exactly how many mendeleyevsthere were： some sources say there were fourteen children； some say seventeen。 all agree； atany rate； that dmitri was the youngest。 luck was not always with the mendeleyevs。 whendmitri was small his father； the headmaster of a local school； went blind and his mother hadto go out to work。 clearly an extraordinary woman； she eventually became the manager of asuccessful glass factory。 all went well until 1848； when the factory burned down and thefamily was reduced to penury。 determined to get her youngest child an education； theindomitable mrs。 mendeleyev hitchhiked with young dmitri four thousand miles to st。
petersburg鈥攖hat鈥檚 equivalent to traveling from london to equatorial guinea鈥攁nd depositedhim at the institute of pedagogy。 worn out by her efforts； she died soon after。
mendeleyev dutifully pleted his studies and eventually landed a position at the localuniversity。 there he was a petent but not terribly outstanding chemist； known more forhis wild hair and beard； which he had trimmed just once a year； than for his gifts in thelaboratory。
however； in 1869； at the age of thirty…five； he began to toy with a way to arrange theelements。 at the time； elements were normally grouped in two ways鈥攅ither by atomic weight（using avogadro鈥檚 principle） or by mon properties （whether they were metals or gases；for instance）。 mendeleyev鈥檚 breakthrough was to see that the two could be bined in asingle table。
as is often the way in science； the principle had actually been anticipated three yearspreviously by an amateur chemist in england named john newlands。 he suggested that whenelements were arranged by weight they appeared to repeat certain properties鈥攊n a sense toharmonize鈥攁t every eighth place along the scale。 slightly unwisely； for this was an ideawhose time had not quite yet e； newlands called it the law of octaves and likened thearrangement to the octaves on a piano keyboard。 perhaps there was something in newlands鈥檚manner of presentation； but the idea was considered fundamentally preposterous and widelymocked。 at gatherings； droller members of the audience would sometimes ask him if he couldget his elements to play them a little tune。 discouraged； newlands gave up pushing the ideaand soon dropped from view altogether。
mendeleyev used a slightly different approach； placing his elements into groups of seven；but employed fundamentally the same principle。 suddenly the idea seemed brilliant andwondrously perceptive。 because the properties repeated themselves periodically； the inventionbecame known as the periodic table。
mendeleyev was said to have been inspired by the card game known as solitaire in northamerica and patience elsewhere； wherein cards are arranged by suit horizontally and bynumber vertically。 using a broadly similar concept； he arranged the elements in horizontalrows called periods and vertical columns called groups。 this instantly showed one set ofrelationships when read up and down and another when read from side to side。 specifically；the vertical columns put together chemicals that have similar properties。 thus copper sits ontop of silver and silver sits on top of gold because of their chemical affinities as metals； whilehelium； neon； and argon are in a column made up of gases。 （the actual； formal determinant inthe ordering is something called their electron valences； for which you will have to enroll innight classes if you wish an understanding。） the horizontal rows； meanwhile； arrange thechemicals in ascending order by the number of protons in their nuclei鈥攚hat is known as theiratomic number。
the structure of atoms and the significance of protons will e in a following chapter； sofor the moment all that is necessary is to appreciate the organizing principle： hydrogen hasjust one proton； and so it has an atomic number of one and es first on the chart； uraniumhas ninety…two protons； and so it es near the end and has an atomic number of ninety…two。
in this sense； as philip ball has pointed out； chemistry really is just a matter of counting。
（atomic number； incidentally； is not to be confused with atomic weight； which is the numberof protons plus the number of neutrons in a given element。） there was still a great deal thatwasn鈥檛 known or understood。 hydrogen is the most mon element in the universe； and yetno one would guess as much for another thirty years。 helium； the second most abundantelement； had only been found the year before鈥攊ts existence hadn鈥檛 even been suspectedbefore that鈥攁nd then not on earth but in the sun； where it was found with a spectroscopeduring a solar e