7/25/2019 Early Atomic and Molecular Theories

1/8

7/25/2019 Early Atomic and Molecular Theories

2/8

The development of Dalton's atom ! theo"# and Avo$ad"o's mole!%la"la& had ove"" d n$ n %en!e on the development of !hem st"#( nadd t on to the " mpo"tan!e n ph#s !s)

EARLY ATOMIC AND MOLECULA

THEORIES

7/25/2019 Early Atomic and Molecular Theories

3/8

Avo$ad"o's la&( &h !h &as eas l# p"oved *# + net ! theo"#( nd !atedthat a spe! ,ed vol%me of a $as at a $ ven tempe"at%"e and p"ess%"eal&a#s !onta ned the same n%m*e" of mole!%les( ""espe!t ve of the $assele!ted) Th s n%m*e"( ho&eve"( !o%ld not *e a!!%"atel# dete"m ned(and the -.th/!ent%"# ph#s ! sts the"efo"e had no so%nd +no&led$e of

mole!%la" o" atom ! mass and s 0e %nt l the t%"n of the 12th !ent%"#(&hen s%*se3%ent to the d s!ove"# of the ele!t"on( the Ame" !anph#s ! st Ro*e"t And"e&s M ll +an !a"ef%ll# dete"m ned ts !ha"$e) Th s,nall# pe"m tted a!!%"ate dete"m nat on of the so/!alled Avo$ad"o'sn%m*e"( &h !h s the n%m*e" of mole!%les n that amo%nt of mate" ale4a!tl# e3%al to ts mole!%la" &e $ht)

A5O6ADRO7S

7/25/2019 Early Atomic and Molecular Theories

4/8

9es des the mass( anothe" 3%ant t# of nte"est &as the s 0e of an atom)5a" o%s and onl# pa"tl# s%!!essf%l attempts at ,nd n$ the s 0e of anatom &e"e made d%" n$ the latte" pa"t of the -.th !ent%"#: the mosts%!!essf%l appl ed the "es%lts of + net ! theo"# to non deal $ases;thats( $ases the *ehav o" of &h !h depended on the fa!t that mole!%les&e"e not po nts *%t had ,n te vol%mes) Onl# late" e4pe" ments nvolv n$the s!atte" n$ of < "a#s( alpha pa"t !les( and othe" atom ! ands%*atom ! pa"t !les *# atoms led to mo"e p"e! se meas%"ements of the "s 0e as *e n$ *et&een -2 /= and -2 /> !m ?@ -2 /> and @ d amete") A p"e! se statement a*o%t the s 0e of an atom( ho&eve"("e3% "es some e4pl ! t de,n t on of &hat s meant *# s 0e( s n!e most

atoms a"e not e4a!tl# sphe" !al and !an e4 st n va" o%s states that!han$e the d stan!e *et&een the n%!le%s and the ele!t"ons & th n the

A5O6ADRO7S

7/25/2019 Early Atomic and Molecular Theories

5/8

One of the most mpo"tant developments lead n$ to the e4plo"at on ofthe nte" o" of the atom( and to the event%al ove"th"o& of the !lass !altheo" es of ph#s !s( &as spe!t"os!op#: the othe" &as the d s!ove"# ofthe s%*atom ! pa"t !les themselves)

S ECTROSCO

7/25/2019 Early Atomic and Molecular Theories

6/8

In -=1 the 9" t sh ast"onome" and !hem st S " Fohn G"ede" !+ 8 ll amHe"s!hel s%$$ested that a !hem !al s%*stan!e m $ht *e dent ,ed *#e4am n n$ ts spe!t"%m;that s( the d s!"ete &avelen$th patte"n n&h !h l $ht f"om a $aseo%s s%*stan!e s em tted) In the #ea"s thatfollo&ed( the spe!t"a of a $"eat man# s%*stan!es &e"e !atalo$ed *# t&o6e"mans( the !hem st Ro*e"t 8 lhelm 9%nsen and the ph#s ! st 6%stavRo*e"t "!hho ) Hel %m &as ,"st d s!ove"ed as a ne& element follo& n$the d s!ove"# of an %ne4pla ned spe!t"al l ne n the s%n's spe!t"%m *#the 9" t sh ast"onome" S " Foseph No"man Lo!+#e" n -=B=) G"om thestandpo nt of atom ! theo"#( ho&eve"( the most mpo"tant !ont" *%t ons&e"e made *# the st%d# of the spe!t"a of s mple atoms( s%!h ash#d"o$en( &h !h sho&ed fe& spe!t"al l nes)

S ECTROSCO

7/25/2019 Early Atomic and Molecular Theories

7/8

D s!"ete l ne spe!t"a o" $ nate f"om $aseo%s s%*stan!es &he"e( n te"msof mode"n +no&led$e( the ele!t"ons have *een e4! ted *# heat o" *#*om*a"dment & th s%*atom ! pa"t !les) In !ont"ast( a heated sol d has a!ont n%o%s spe!t"%m ove" the f%ll v s *le "an$e and nto the nf"a"ed and%lt"av olet "e$ ons) The total amo%nt of ene"$# em tted depends st"on$l#on the tempe"at%"e( as does the "elat ve ntens t# of the d e"ent&avelen$th !omponents) As a p e!e of "on s heated( fo" e4ample( ts"ad at on s ,"st n the nf"a"ed spe!t"%m and !annot *e seen: t thene4tends nto the v s *le spe!t"%m &he"e the $lo& sh fts f"om "ed to&h te as the pea+ of ts "ad ant spe!t"%m sh fts to&a"d the m ddle of thev s *le "an$e)

S ECTROSCO

7/25/2019 Early Atomic and Molecular Theories

8/8

Attempts to e4pla n the "ad at on !ha"a!te" st !s of sol ds( %s n$ thetools of theo"et !al ph#s !s ava la*le at the end of the -.th !ent%"#( ledto the p"ed !t on that at an# $ ven tempe"at%"e the amo%nt of "ad at onn!"eased & th f"e3%en!# and & tho%t l m t) Th s !al!%lat on( n &h !h noe""o" &as fo%nd( &as n d sa$"eement & th e4pe" ment and also led toan a*s%"d !on!l%s onJ A *od# at a ,n te tempe"at%"e !o%ld "ad ate ann,n te amo%nt of ene"$#) Th s "e3% "ed a ne& &a# of th n+ n$ a*o%t"ad at on and( nd "e!tl#( a*o%t the atom)

S ECTROSCO