chapter2 - J ohn D a l ton (1766-1844) Publ i shed four...

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Unformatted text preview: J ohn D a l ton (1766-1844) Publ i shed four postul a tes descr i bi ng the funda menta l s of ma tter a nd the exi stence of a toms & el ements. J .J . T homson (1856-1940) Pr oposed i n 1897 tha t Ca thode Ra ys wer e r ea l l y nega ti vel y cha r ged pa r ti cl es tha t we now know a r e el ectr ons. T homson's Ca thode Ra y Exper i ment The el ectr on's char ge-to-mass r ati o = 1.76 108 C/ g Rober t M i l l i ken (1868-1953) D eter mi ned the cha r ge of a n el ectr on to be 1.60 10-19 C fr om thi s the ma ss coul d be ca l cul a ted to be 9.11 10-28 g M i l l i ka n's Oi l D r op Exper i ment Er nest Ruther for d (1871-1937) U ncover ed the na tur e of & r a ys. Pr oposed nucl ea r model of the a tom. , a nd Ra di a ti on -28 -ray H i gh speed el ectr on: char ge= -1, mass= 9.11 10 -ray El ectr omagneti c Radi ati on: no char ge, no mass g -ray H e cor e: char ge= +2, mass= 7295 mass of el ectr on T homson's Pl um Puddi ng M odel of the Atom Ruther for d's Gol d Foi l Exper i ment N ucl ea r Pi ctur e of the Atom M ost of the ma ss a nd a l l of the posi ti ve cha r ge r esi de i n a ver y sma l l r egi on ca l l ed the nucl eus (conta i ni ng pr otons a nd neutr ons). M ost of the vol ume a nd a l l of the nega ti ve cha r ge a r e occupi ed by el ectr ons sur r oundi ng the nucl eus. Pa r ti cl e Cha r ge Pr oton Neutr on +1 0 M a ss (g) 1.6727 10-24 1.6750 10-24 -28 M a ss (a mu) 1.007316 1.008701 Per i odi c T a bl e Gr oup 1 (1A) Gr oup 2 (2A) Al ka l i M eta l s Al ka l i ne-Ea r th M eta l s Gr oups 3-12 T r a nsi ti on M eta l s Gr oup 16 (6A) Cha l cogens Gr oup 17 (7A) H a l ogens Gr oup 18 (8A) N obl e Ga ses Si l i con: Pr ototypi ca l M eta l l oi d Shi ny meta l l i c l ustr e Br i ttl e D i a mond Cr ysta l Str uctur e Pur e Si i s a n i nsul a tor The conducti vi ty of Si can be i ncr eased and contr ol l ed by addi ng i mpur i ti es. M ol ecul a r Substa nces I n a mol ecul ar substance the atoms shar e val ence el ectr ons to for m str ong coval ent bonds that hol d the mol ecul es together . The attr acti on between mol ecul es ar e often weak, expl ai ni ng why gases and l i qui ds ar e common among mol ecul ar substances. Cova l ent Substa nces wi thout M ol ecul es M eta l l i c Substa nces I n a metal a sea of negati vel y char ged val ence el ectr ons move fr eel y about the posi ti vel y char ged metal i on cor es. I oni c Substa nces I n an i oni c compound the metal atoms gi ve up some el ectr ons to for m posi ti vel y char ged cati ons, those el ectr ons go to the non-metal s that for m negati vel y char ged ani ons. The attr acti on between cati ons and ani ons hol ds the i oni c compound together . Pr edi cti ng I oni c Cha r ges Zn 2+ Ag+ Wi thi n l i mi ts el ements tend to gai n (non-metal s) or l ose (metal s) enough el ectr ons to attai n the same el ectr on count as the near est nobl e gas. Thi s becomes i ncr easi ngl y di ffi cul t as you move towar d the center of the per i odi c tabl e. Pol ya tomi c I ons ...
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