In , a wild-haired Russianchemist had an extraordinary vision.Hed been struggling witha mysterythat had perplexedscientists for generations.And for the very first time, hedglimpsed natures building blocks,the elements,arranged in their natural order.His name was Dmitri Mendeleev,and he was on the brink of crackingthe secret code of the Cosmos,what was to become one of mansmost beautiful creations,the Periodic Table of Elements.This is the story of those elements,the building blocks that make upthe universe.the remarkable taleof their discovery,and how they fit together, revealshow the modern world was made.My names Jim Al-Khalili.And ever since I started studyingthe mysteries of matter,Ive been fascinated bychemistrys explosive history.Ho-ho! Brilliant!.Ive discovered someexciting elements.Thats fantastic!.and Ive seen how chemistrywas forgedin the furnaces of the alchemists.Now Im going to continuemy journey.Ill take up the questof the chemical pioneers.Well, my arms burning up.as they struggled to make senseof elemental chaosand conquerour fundamental fear of disorder.Could there be a grand planunderlying the elements?Ill take part in somevolatile experiments.Now were going to dropin the potassium.Wow, look at that! Wahey!.and witness somefiery reactions.And Ill find out how the hiddenorder of the natural worldwas revealed in all its glory -the order of the elements.As a nuclear physicist,Ive spent a lifetime studyingthe sub-atomic world,the basic building blocksof matter.But to do that, I need to understandthe ingredients of OUR world.the elements.Our planet was createdfrom just elements.The ground we walk on, the air thatwe breathe, the stars we gaze at,even us.Our bodies areentirely made of elements.We now know the name and numberof every naturally-occurringelement in existence.But years ago,those elements were only justbeginning to give up their secrets.At the beginningof the th century,only had been discovered,from liquid mercuryto dazzling magnesium.and volatile iodine.Scientists had no idea how many morethey might find,or whether therecould be an infinite number.But the big question was,how did they fit together?Were they random stars,or was the elemental world born oforder and logic?Solving the puzzle would proveto be a daunting challenge.And the first glimmerings of ananswer came from an unlikely source.John Daltonwas an intelligent, modest man,and he had onevery British passion - the weather.He was born herein the Lake District in .He was so clever, thatas a young boy, just years old,he was already teaching other kidsat a school that he set up.Walking home, he loved watchingthe weather systemssweeping across the fells.He was so obsessed that he kepta meteorological diary for years,and every single day,come rain or shine,he entered his preciseobservations - , of them.Dalton was a quiet,retiring man with modest habits.He was a lifelong bachelor, with notmuch in the way of a social life.His only recreationwas a game of bowls once a week,every Thursday afternoon.He was certainlya creature of habit,and he might sound a bit dull.But actually, Dalton wasan avid reader and a deep thinker.Underneath his mild-manneredexterior,his head was teemingwith radical ideas.Now scientists had recentlydiscovered something very importantabout the way elements combineto form compounds.When they do so, they always combinein the same proportions.Dalton would have known thattable salt, sodium chloride,is always made up of one partsodium and one part chlorine.So it doesnt matter whether thesalt comes from Salt Lake Cityor Siberia, its always in the sameproportion by weight, every time.Dalton reckoned for this to happen,each element had to be made upof its own unique building blocks,what he calledultimate particles, atoms.It was a blinding illumination,completely left field.Everything, he suggested,the entire universe,was made up of infinitesimallysmall particles.The Greeks had hit on the ideaof the atom , years earlier,but abandoned it.Now, Dalton took up the batonwith his own theory of matter.What Dalton was describingwas revolutionary.He had struck on the foundationsof atomic theory,foreshadowing research that wouldntbe proved until a century later.He proposed that there are as manykinds of atomsas there are elements.And just as each elementis different,so each elements atom hasa different weight -a unique atomic weight.Every element has its own signatureatomic weight,whether it be a solid,a liquid, or even a gas.These three balloons are eachfilled with a different gas.Now they are roughlythe same