Chapter 8: Electron Configurations and Periodicity

Transcription

1 Elctron Spin & th Pauli Exclusion Principl Chaptr 8: Elctron Configurations and Priodicity 3 quantum numbrs (n, l, ml) dfin th nrgy, siz, shap, and spatial orintation of ach atomic orbital. To xplain how lctrons populat atomic orbitals in an atom, w nd a 4th quantum numbr. 4. spin quantum numbr, ms lctrons bhav lik thy ar spinning around an axis spinning of a chargd particl crats a magntic fild magntic fild cratd has a dirction if spins clockwis, magntic fild is on dirction (ms = +!) if spins countr-clockwis, magntic fild is opposit dirction (ms =!) Exprimntal Evidnc of Elctron Spin: Strn & Grlach (1921)

2 How Do Elctrons Populat Atomic Orbitals? Pauli Exclusion Principl (1925) No 2 lctrons in an atom can hav th sam st of 4 quantum numbrs. n, l, ml dfin th atomic orbital ms will dfin th lctrons in th orbital If thr ar only 2 possibl ms valus, thn ach atomic orbital can hold no mor than 2 lctrons; spcifically, on must hav ms = +! and th othr must hav ms =! Ths 2 s in an atomic orbital ar said to b spin-paird. Effctiv Nuclar Charg (Zff) What is th charg flt by an lctron in an atom? dpnd on n and l of th orbital whr th livs th farthr th lctron is from th nuclus: th lss th forc of attraction to th nuclus th gratr th - rpulsion an outr shll lctron is shildd by innr shll s Effctiv Nuclar Charg (Zff) Zff = Zactual shilding factor Zff and Atomic Orbitals rlationship btwn Zff and n probability of an bing clos to th nuclus: n = 1 > n = 2 > n = 3 Zff flt by an in an orbital: n = 1 > n = 2 > n = 3 nrgy of orbital: n = 1 < n = 2 < n = 3

3 Zff and Atomic Orbitals rlationship btwn Zff and l (within a sam shll) probability of an bing clos to th nuclus: l = 0 > l = 1 > l = 2 or: s > p > d Zff flt by an in an orbital: l = 0 > l = 1 > l = 2 or: s > p > d nrgy of orbital: s < p < d Elctron Configurations giv complt lctronic dscription for vry lmnt prdict orbitals occupid by lctrons writ lctron configurations draw orbital diagrams follow st of 3 ruls: Aufbau ( building up ) Principl ach succssiv lctron will go into th lowst nrgy orbital availabl this rsults in th lowst nrgy, ground stat configuration Th Aufbau Principl 1. Lowr nrgy orbitals fill bfor highr nrgy orbitals. us th Rlativ Enrgis of Atomic Orbitals diagram In What Ordr Do Atomic Orbitals Populat? Lowr Enrgy to Highr Enrgy 2. An orbital can accommodat a maximum of 2 s which must b spin-paird. Pauli Exclusion Principl 3. Hund s Rul: If 2 or mor dgnrat orbitals ar availabl, on will go into ach orbital until all ar half-full. th s in th singularly populatd orbitals must hav th sam ms Aftr all dgnrat orbitals ar half-full, thn a 2nd may b addd to fill th orbitals.

4 xampls: Writ th ground stat lctron configurations, and complt an orbital diagram for nutral atoms of th following lmnts. N (7 ) : 1s 2 2s 2 2p 3 1s 2s 2p Al (13 ) : 1s 2 2s 2 2p 6 3s 2 3p 1 1s 2s 2p 3s 3p Closd Shlls and Subshlls & Using Nobl Gas Cor Symbolism in Elctron Configurations Sc (21 lctrons): 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 1s 2s 2p 3s 3p 4s 3d Ga (31 lctrons): [Ar] 4s 2 3d 10 4p 1 4s 3d 4p Som Trminology: innr shll lctrons outr shll lctrons cor lctrons valnc lctrons paramagntic diamagntic

5 Som Anomalis in Elctron Configurations: rsult from unusual stability of half-filld or compltly filld shlls or subshlls x: Cr prdict: [Ar] 4s2 3d4 4s 3d x: Cu prdict: 4s! 3d actual: [Ar] 4s1 3d5 4s [Ar] 4s2 3d9! 4s 3d actual: [Ar] 4s1 3d10 3d havy lmnts (abov atomic # 40) E btwn orbitals is smallr, so anomalis ar common Elctron Configurations and th Priodic Tabl

6 Priodic Trnds Th goal is to us our undrstanding of lctron configurations and Zff to undrstand trnds in: atomic radius ionization nrgy lctron affinity How dos a givn proprty chang from lft to right across priodic tabl? How dos a givn proprty chang from top to bottom of priodic tabl? configuration d c r a s Priodic Trnd in Zff incras Effctiv Nuclar Charg, Zff Na Mg Al Si P S Cl Ar [N]3s 1 [N]3s 2 [N]3s 2 3p 1 [N]3s 2 3p 2 [N]3s 2 3p 3 [N]3s 2 3p 4 [N]3s 2 3p 5 [N]3s 2 3p 6 actual nuclar charg # cor s # valnc s Zff Atomic Radius radius (typically in pm or Å) of nutral atoms of lmnts Priodic Trnd in Atomic Radius trnd: atomic radius dcrass lft to right across th priodic tabl atomic radius incrass top to bottom of th priodic tabl i n c r a s dcras Atomic Radius

7 Ionization Enrgy Priodic Trnd in Atomic Radius ionization nrgy th nrgy rquird to rmov an lctron from a gas phas atom or ion in its ground stat X (g) " X+ (g) + ; d c r a s Priodic Trnd in Ionization Enrgy ndothrmic incras Ionization Enrgy Priodic Trnd in Ionization Enrgy considr succssiv ionization nrgis: M (g)! M+ (g) + M+ (g)! M2+ (g) + M2+ (g)! M3+ (g) + Not th unxpctd changs btwn groups IIA & IIIA, and groups VA & VIA. Why? Think about configurations. 1st ionization nrgy 2nd ionization nrgy 3rd ionization nrgy It bcoms succssivly hardr to rmov an from a positivly chargd spcis bcaus of forcs of lctrostatic attraction.

8 Priodic Trnd in Ionization Enrgy rmoving a cor costs MUCH mor nrgy than rmoving a valnc Elctron Affinity lctron affinity chang in nrgy that occurs whn an lctron is addd to an isolatd gas phas atom. X (g) +! X (g) * d c r a s * incras Elctron Affinity Valnc lctrons ar most asily lost during ionization, and ar gaind, lost, or shard during chmical ractions. * incras mans bcoms largr, ngativ valu mor favorabl for anion formation; dcras mans bcoms smallr, ngativ valu lss nrgy rlasd and lss favorabl for anion formation Priodic Trnd in Elctron Affinity not: whr lctron affinity valus ar > 0, anion formation is vry unfavorabl; alkalin arth mtals & th nobl gass

9 Priodic Trnd in Elctron Affinity