1 ATOMIC STRUCTURE Fudamtal Particls: Mai Fudamtal Particl : (a) Elctro: It is a fudamtal particl of a atom which carris a uit gativ charg. It was discovrd by J.J. Thomso (1897) from th studis carrid out o cathod rays i th discharg tub. Wh a high voltag currt (10, 000 volts) is passd btw two lctrods i a discharg tub cotaiig a gas (which is a poor coductor of lctricity) at a vry low prssur (0.01 mm Hg), a stram of gativly chargd particls flow from cathod (mtal rod) to aod. Ths rays wr calld cathod rays & cosistd of stram of gativly chargd particls calld lctros. Proprtis : It is th lightst particl also kow as - particls It carris 1.6 10 19 coulombs or 4.8 10 10 su charg. It s mass is about 1/1837 tims th mass of hydrog atom. Thus mass of lctro is 8 9.1 10 gm or 31 9.1 10 kg or 0.0005486 amu. Th /m ratio of lctro is costat irrspctiv of th atur of th gas & th mtal, usd i discharg tub xprimt. Ratio of /m, as stimatd by Thomso is 8 1.7610 coulombs / gm 0 It is rprstd by 1. 13 Radius of lctro is.8 10 cm. (b) Proto: A atom is lctrically utral ad lctro cotai gativ charg, it follows that a qual magitud of positiv lctricity must also b prst i a atom. Goldsti (1886), wh usd prforatd cathod i discharg tub xprimt foud that i additio to cathod rays, thr ar positiv rays, calld caal rays; movig i th opposit dirctio. By studyig th bhaviours of ths rays i lctro & magtic fild, ths rays wr foud to cosist of havy positivly chargd particls, calld protos. Proprtis: It cotai 1.6 10 19 coulombs or 10 4.8 10 su charg. Th mass of proto is arly qual to that of th hydrog. It is 1.67 10 kg or 4 1.67 10 gm or 1.0078 amu /m ratio for proto dpds o th gas tak i th discharg tub xprimt. /m of proto is 38 9.5810 coulomb/gm Volum of proto is 38 3 1.5 10 cm or uclar dsity is of th ordr of 10 gm/cm 3. (c) Nutro: Chadwick (193) discovrd that wh Bryllium was bombardd by particl, a subatomic particl of mass slightly gratr tha proto & utral i origi obtaid. It is calld utro. It is ot dflctd by lctric ad magtic fild. Proprtis: It has mass 4 1.675 10 gm or 7 1.675 10 kg or 1.00866 amu It is havist particl of a atom. Nutro ad proto rsids at th ctr of atom calld uclus. Nutro ad proto togthr calld as uclos. Nutro ca disitgrat ito proto ad utro. 7 14 H.O.: 8-A/11, Jia Sarai, Nar-IIT, Nw Dlhi-16, Ph : 011-6851008, 6861009 www.carrdavour.i B.O.: 48, First Floor, Mall Road, G.T.B. Nagar (Mtro Gat No. 3), Dlhi-09, Ph: 011-654644, 95409991
Som Ucommo Fudamtal particls: 0 (i) Positro : 1 - It is th positiv coutrpart of lctro, discovrd by Adrso (193). It is vry ustabl ad combis with lctro producig rays (ii) Nutrio: Ths ar discovrd by Paullig (1934) & hav small ( 0) mass ad zro charg. (iii) Atiutrio: Ths wr discovrd by Frmi (1934) & is idtical to utrio but havig opposit spi. (iv) Msos: Ths wr discovrd by Yukawa (1935). Thy may b positivly, gativly or utral. Thir mass is itrmdiat btw that of a lctro ad a proto. Msos Charg Mass / 86 m / / 0 70 m k / / 0 970 m (v) Atiproto: It mass is qual to a proto ad charg is qual to a lctro. (vi) Atutro: It s mass is qual to a utro ad charg is qual to zro. It is idtical to utro but opposit spi. Som Importat Dfiitios: (i) Isotops: Th atoms of a lmt which hav th sam atomic umbrs but diffrt atomic mass. Thy hav sam chmical proprtis but diffrt physical proprtis. Isotops hav diffrt umbr of utros. (i) 16 8 O, 17 8 O,18 8 O (ii) 1 1 H, 3 14 15 1 H, 1H (iii) 7 N, 7 N (ii) Isobars: Diffrt atoms which sam atomic masss but diffrt atomic umbrs. 40 40 40 18 Ar, 19K, 0Ca (iii) Isotos: Thos which cotai sam umbr of utro. 30 31 3 14 Si, 15P, 16S (iv) Isolctroic: Thos atoms or io which hav sam o. of lctros ar kow as isolctroic. 17 Cl, 18 Ar, 19 K, 0 Ca (vi) Isodiaphrs: Th lmt which hav th sam valu of (N P) is calld isodiaphrs. 7 9 11 13 3 Li, 4B, 5 B, 6 C H.O.: 8-A/11, Jia Sarai, Nar-IIT, Nw Dlhi-16, Ph : 011-6851008, 6861009 www.carrdavour.i B.O.: 48, First Floor, Mall Road, G.T.B. Nagar (Mtro Gat No. 3), Dlhi-09, Ph: 011-654644, 95409991
3 Bohr s thory of hydrog atom It dpds upo Max Plack s Quatum thory. Postulats: Nils Bohr (1913) (i) Th lctros travl i orbits that hav discrt quatizd spds & thrfor, quatizd rgis. That is, ot vry orbit is possibl but oly crtai spcific os, at crtai spcific distacs from uclus. (ii) Th lctros do ot cotiuously los rgy as thy travl. Thy ca oly gai & loos rgy by jumpig from o allowd orbit to aothr. (iii) Wh a lctro maks a jump from o orbit to aothr, th rgy diffrc is carrid away (or supplid) by a sigl quatum of light (calld a photo) which has a rgy qual to th rgy diffrc btw two orbit. (iv) Th frqucy of th mittd photo is o ovr th classical orbit priod, corrspodig to th classical missio frqucy. (v) Elctro ca mov oly i thos orbit i which thir agular momtum is a itgral multipl of h/. h i.. mvr Thus agular momtum is quatizd. Applicatio of Bohr s thory: 1. Radius of th orbit: For H ad H lik atoms Li, B h r 4 m whr h = Plack s costat, m = mass of lctro, = charg o lctro = atomic umbr, = orbit umbr O puttig valu of kow costat. r 0.59 Å z. Vlocity of a lctro i th shll: v ; h 8 v.18810 cm / sc 3. Ergy of lctro i th orbit: E 4 m h H.O.: 8-A/11, Jia Sarai, Nar-IIT, Nw Dlhi-16, Ph : 011-6851008, 6861009 www.carrdavour.i B.O.: 48, First Floor, Mall Road, G.T.B. Nagar (Mtro Gat No. 3), Dlhi-09, Ph: 011-654644, 95409991
Pottial rgy Total rgy kitic rgy 19 (i) Total rgy 13.6 V/atom 131 kj/mol.1810 J/atom Ioisatio Ergy: Durig ioisatio a lctro movs from lowst rgy stat to ifiity, whr thr is o forc of attractio ad thus E 0 E E E 1 0 13.6 V/atom ; E 13.6 V/atom Elctromagtic Radiatios: Th radiatios which do ot dviat from lctric ad magtic fild, ad travl i vacuum with spd of light. : Radio wavs, microwavs, X-rays, rays, I.R. UV, visibl ad Cosmic rays. Emissio Spctrum of hydrog: Durig th display of missio spctrum, matrial is radiatd with hat or lctricity, this causs xcitatio of lctro by absorptio of rgy. O rlaxatio this absorbd rgy is lost as light radiatio ad givs missio spctrum. I missio spctrum of hydrog atom, thr ar six typs of missio lis. It ca b xplaid by takig a sampl of hydrog which cotai millios of hydrog atom. Thus diffrt atoms absorb diffrt amout of rgy ad th rlaxs upto diffrt lvl. Thus givs various spctral li. Th wavlgth or wavumbr of light ca b obtaid by rgy diffrc btw two lvls. 4 4 hc m 1 1 ; h 1 Whr, 4 4 m m E.h 1 h 1 1 V R H cm 1 1 1 V = wavumbr; R H = Rydbrg costat (109677 cm 1 ) (E ) E= E - E 1 (E ) 1 1 1 1 V 109677 1 M = 8 = 7 = 6 = 5 = 4 = 3 Pasch Bracktt pfud Humphry I.R. rgio = M = 1 Lyma UV- rgio Balmr visibl rgio H.O.: 8-A/11, Jia Sarai, Nar-IIT, Nw Dlhi-16, Ph : 011-6851008, 6861009 www.carrdavour.i B.O.: 48, First Floor, Mall Road, G.T.B. Nagar (Mtro Gat No. 3), Dlhi-09, Ph: 011-654644, 95409991
(i) For Lyma sris : 1 1,,3,4,5... (ii) For Balmr Sris: 1 ; 3,4,5,6... (iii) For Pasch sris: 1 3 ; 4,5,6,7... ; (iv) For Bracktt sris: 1 4; 5,6,7,8... (v) For pfud Sris: 1 1 V R H 1 1 1 V R H 1 1 V R H 3 1 1 V R H 4 1 5 ; 6,7,8,9 ; 1 1 V R H 5 (vi) For Humphry Sris: 1 1 1 6 ; 7,8,... V R H 6 Not: If a lctro from th xcitd stat coms to various rgy stats, th maximum spctral lis obtaid 1 will b. Limitatios of Bohr s thory: (i) It fails to xplai spctra to atoms with mor tha o lctro. It ca oly xplai th spctra of hydrog ad sigl lctro spcis lik 3 H, Li, B tc. (ii) It dos ot xplai fi structur of spctral lis. (iii) It dos ot xplai ma ffct (Splittig up of spctra lis i prsc of a magtic fild) & stark ffct (splittig up of spctral lis i prsc of a lctric fild) (iv) Fails to rcogis wav proprty of lctro propod by d Brogli. Wav - Particl Duality of Mattr/d-brogli quatio: All th discrt particls of mattr i motio ( lctro, proto, utro, atoms ad molculs) possss particl as wll as wav charactristics, i.. dual charactr is ot oly possssd by radiatio but also by all th microscopic particls of mattr. It mas that a lctro or othr microscopic particl is ithr a particl or a wav. It is a tity which is capabl of dvlopig o of ths faturs dpdig upo th typ of th itractio with xtral world. d-brogli s quatio: From Plack quatio, E hv, c hc E... (1) 5 H.O.: 8-A/11, Jia Sarai, Nar-IIT, Nw Dlhi-16, Ph : 011-6851008, 6861009 www.carrdavour.i B.O.: 48, First Floor, Mall Road, G.T.B. Nagar (Mtro Gat No. 3), Dlhi-09, Ph: 011-654644, 95409991