Noble gas configuration. Atoms of other elements seek to attain a noble gas electron configuration. Electron configuration of ions

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1 Valnc lctron configuration dtrmins th charactristics of lmnts in a group Nobl gas configuration Th nobl gass (last column in th priodic tabl) ar charactrizd by compltly filld s and p orbitals this is a vry stabl valnc lctron configuration nobl gass typically xist as singl atoms and do not radily form compounds with othr lmnts 1s N 1s s p 6 Th chmical bhavior and proprtis of lmnts in a group ar associatd with th valnc lctron configuration of its lmnts 1s s p 6 s p 6 Etc. Atoms of othr lmnts sk to attain a nobl gas lctron configuration For most lmnts, attaining a nobl gas configuration mans having 8 valnc lctrons (two s lctrons and six p lctrons) -- this is calld a full valnc shll (also rfrrd to as an octt ) Nobl gass ar highly unractiv and do not radily form compounds Th rst of th lmnts in th priodic tabl tnd to combin with othr lmnts to form compounds Whn forming compounds, th atoms of ths lmnts los, gain, or shar lctrons to attain a stabl valnc lctron configuration (i.., idntical to nobl gass) Atoms that attain a nobl gas configuration by losing or gaining lctrons (i.., forming ions) form ionic bonds Atoms that attain a nobl gas configuration by sharing lctrons form covalnt bonds 10 N X 86 1s 1s s p 6 1s s p 6 s p 6 5s 4d 10 5p 6 For th lmnts in Priod 1 (hydrogn and hlium), a full valnc shll consists of valnc lctrons (two s lctrons) this is bcaus th first principal nrgy lvl () dos not hav a p sublvl (i.., no p orbitals) 5s 4d 10 5p 6 6s 4f 14 5d 10 6p 6 Alkali mtals ar highly ractiv bcaus thy can obtain a stabl nobl gas configuration by losing on lctron Elctron configuration of ions Cs 87 Fr 1s s 1 1s s p 6 s 1 1s s p 6 s p 6 4s 1 5s 1 5s 4d 10 5p 6 6s 1 5s 4d 10 5p 6 6s 4f 14 5d 10 6p 6 7s 1 10 N X 86 1s 1s s p 6 1s s p 6 s p 6 5s 4d 10 5p 6 5s 4d 10 5p 6 6s 4f 14 5d 10 6p 6 Anions (ngativ ions): Formd by adding lctrons to nutral atoms lctrons ar addd to th mpty or partially mpty orbital with th lowst valu of n Exampl: Oxygn (O) Numbr of lctrons: 8 Oxid (O - ) Numbr of lctrons: 10 1s s p 4 1s s p 6 [N]

2 Elctron configuration of ions Cations (positiv ions): Formd by rmoving lctrons from nutral atoms Elctron configuration of ions Cations (positiv ions): Formd by rmoving lctrons from nutral atoms lctrons ar rmovd first from occupid orbitals with th highst principal quantum numbr n if thr is mor than on occupid subshll for a givn valu of n, lctrons ar first rmovd from th orbital with th highst valu of l For atoms containing occupid d subshlls: lctrons ar rmovd from th ns and np subshlls bfor thy ar rmovd from th (n-1)d subshll Exampl: thium () Numbr of lctrons: thium ion ( ) Numbr of lctrons: 1s s 1 1s [] Elctron configuration of ions Cations (positiv ions): Formd by rmoving lctrons from nutral atoms Exampl: Elctron configuration of ions Iron (F) Numbr of lctrons: 6 Exampl: Aluminum (Al) Numbr of lctrons: 1 1s 4s d 4p [] 4s d 6 1s s p 6 s p 1 Aluminum ion (Al ) Numbr of lctrons: 10 1s s p 6 [N] Iron (II) (F ) Numbr of lctrons: 4 1s 4s d 4p Iron (III) (F ) Numbr of lctrons: 1s 4s d 4p [] d 6 [] d 5 Elctron configuration of ions Elctron configuration of ions Exampl: Tin (Sn) Numbr of lctrons: 50 1s 5s 4d 5p Tin (II) (Sn ) Numbr of lctrons: 48 [] 5s 4d 10 5p Exampl: Strontium (Sn) Numbr of lctrons: 8 [] 5s 4s d 4p 5s 4d 1s 5s 4d 5p [] 5s 4d 10 Strontium ion (Sn ) Numbr of lctrons: 6 [] Tin (IV) (Sn 4 ) Numbr of lctrons: 46 1s 5s 4d 5p [] 4d 10 4s d 4p 5s 4d

3 Priodic proprtis of th lmnts Crtain physical/chmical proprtis of atoms follow prdictabl trnds in th priodic tabl as you mov: down a column (group) from lft to right across a row (priod) Ths ar calld priodic proprtis bcaus thy follow a pattrn that rpats itslf for ach row of lmnts (priod) in th priodic tabl priodicity -- charactrizd by a rpating or rcurrnt cycl ( priod ) Priodic proprtis includ: ionic radius ionization nrgy lctron affinity Ths proprtis dpnd on how strongly thir outr lctrons ar attractd to th nuclus Concpt of ffctiv nuclar charg Many proprtis of atoms dpnd on how strongly thir outr lctrons ar attractd to th nuclus Exampl: thium Elctrons fl an attractiv forc to th positivly chargd protons in th nuclus (lctrostatic forc) From Coulomb s law: Th forc is proportional to th magnitud of th charg in th nuclus mor protons = strongr forc At th sam tim, lctrons fl rpulsiv forcs from th othr ngativly chargd lctrons in th atom Concpt of ffctiv nuclar charg Many proprtis of atoms dpnd on how strongly thir outr lctrons ar attractd to th nuclus Cor lctrons scrn nuclar charg mor ffctivly than lctrons in th sam shll Exampl: thium Th nt rsult is that lctrons ar attractd to th nuclus, but not as strongly as thy would b if thr wr no othr lctrons prsnt th outr lctrons ar partially shildd from th nuclar charg by th innr lctrons outr lctrons fl an an ffctiv positiv charg from th nuclus that is lss than th actual charg For an lctron in th s orbital of a lithium atom, th ffctiv nuclar charg is 1. (actual nuclar charg is ) Exampl: Bryllium Cor lctrons ar vry ffctiv at shilding outr lctrons from th charg containd in th nuclus cor lctrons ar innr lctrons -- i.., lctrons in lowr-nrgy lctron shlls Elctrons in th sam valnc shll do not shild ach othr vry ffctivly from nuclar charg th valnc shll is th outrmost shll -- i.., highst-nrgy lctron shll (highst valu of n) Calculating ffctiv nuclar charg Th ffctiv nuclar charg (Zff) flt by an lctron in an atom can b calculatd as follows: Zff = Z S Calculating ffctiv nuclar charg Exampl: What is Zff flt by a valnc lctron in a lithium atom? Atomic numbr: Z = Elctron configuration: 1s s 1 No. of protons in nuclus (atomic numbr) Scrning constant Mthod 1: S = numbr of cor lctrons = Th scrning constant (S) is a positiv numbr that rprsnts th amount of nuclar charg scrnd by othr lctrons in th atom Th valu of S can b dtrmind by th following mthods: 1) Assum that it is qual to th numbr of cor lctrons in th atom ) Us Slatr s ruls -- othr lctrons in th sam shll contribut 0.5 to S -- lctrons in th nxt lowr shll (n-1) contribut 0.85 to S -- lctrons in lowr shlls (n-, n-, tc.) contribut 1.00 to S Zff = Z S = = 1 Mthod : Valnc lctron is in th shll Numbr of othr lctrons in th sam shll = 0 Numbr of lctrons in th nxt lowr shll () = Numbr of lctrons lowr shlls = 0 S = (0 x 0.5) ( x 0.85) (0 x 1.00) = 1.7 Zff = Z S = = 1.

4 Calculating ffctiv nuclar charg Exampl: What is Zff flt by a valnc lctron in a chlorin atom? Atomic numbr: Z = 17 Elctron configuration: 1s s p 6 s p 5 Priodicity: Atomic radius Atomic radius -- th distanc btwn th nuclus of an atom and its outrmost (i.., valnc) lctrons Mthod 1: S = numbr of cor lctrons = 10 Zff = Z S = = 7 Mthod : Valnc lctron is in th n = shll Numbr of othr lctrons in th sam shll = 6 Numbr of lctrons in th nxt lowr shll () = 8 Numbr of lctrons lowr shlls () = S = (6 x 0.5) (8 x 0.85) ( x 1.00) = 10.9 Zff = Z S = = 6.1 Atomic radius incrass Atomic radius dcrass Going down a group, atomic radius incrass Going across a priod, atomic radius dcrass s 1 atom s 1 atom 4s 1 atom Atomic radius -- th distanc btwn th nuclus of an atom and its outrmost (i.., valnc) lctrons Distanc btwn nuclus and valnc lctron Atomic radius incrass going down a group in th priodic tabl as th principal nrgy lvl (n) incrass, lctrons ar found on avrag farthr away from th nuclus Priods A (1) A () Groups A (1) 4A (14) 5A (15) DECREASING RADIUS 6A (16) 7A (17) B B C N O F Mg Ca Sr Al Si P S Cl Ga G As S Br In Sn Sb T I 8A (18) N X ow can th siz of th atom dcras as mor lctrons ar addd? Rmmbr that for all of th lmnts in a givn priod, th valnc lctrons occupy th sam principal nrgy lvl ffctiv nuclar charg incrass from lft to right across a priod thium 1 valnc lctron in principal nrgy lvl protons in nuclus ffctiv nuclar charg = 1. R Bryllium valnc lctrons in principal nrgy lvl 4 protons in nuclus ffctiv nuclar charg = 1.95 RB Priod 1 Priod Priodicity: Atomic radius Priod Priod 4 Priod 5 Cs Priod 6 X N Th ffctiv nuclar charg flt by valnc lctrons in B is gratr than th ffctiv nuclar charg flt by valnc lctrons in th valnc lctrons of B ar pulld in closr ( RB < R )

5 Ionization nrgy Ionization nrgy -- th nrgy rquird to rmov th last tightly bound lctron (i.., a valnc lctron) from th ground stat of an atom in th gasous stat Exampl: thium (g) 50 kj / mol Ionization nrgy (g) - Ionization nrgy masurs th as with which an atom loss an lctron Th lowr th valu, th mor radily th atom loss an lctron Ionization nrgy trnds Ionization nrgy gnrally incrass moving lft to right across a row of lmnts (priod) in th priodic tabl ffctiv nuclar charg incrass from lft to right across a priod valnc lctrons ar mor strongly bound to th atom, rquiring highr nrgy to pull thm away Ionization nrgy dcrass moving down a column (group) in th priodic tabl valnc lctrons ar situatd farthr away from th nuclus (this ovrcoms th slight incras in ffctiv nuclar charg moving down a column) th forc binding valnc lctrons to th atom is wakr, rquiring lss nrgy to pull thm away Ionization nrgy Priodicity: Ionization nrgy Priod 1 Priod Priod Priod 4 Priod 5 Priod 6 Ionization nrgy incrass Ionization nrgy dcrass N X Cs In gnral: Ionization nrgy is low for mtals and high for non-mtals Succssiv ionization nrgis Succssiv ionization nrgis First ionization nrgy (I1): Th nrgy rquird to rmov th first lctron from a nutral atom Mg(g) Mg (g) - I1 = 78 kj / mol Scond ionization nrgy (I): Th nrgy rquird to rmov th scond lctron from a nutral atom Mg (g) Mg (g) - I = 1450 kj / mol Third ionization nrgy (I): Th nrgy rquird to rmov th third lctron from a nutral atom Mg (g) Mg (g) - I = 770 kj / mol I = 770 kj / mol n = Magnsium ( Z = 1 ) I1 = 78 kj / mol For any givn lmnt, ionization nrgis incras as succssiv lctrons ar rmovd: I1 < I < I... As lctrons ar rmovd, th rmaining lctrons ar lss shildd from th nuclus I = 1450 kj / mol ffctiv nuclar charg incrass lctrons ar mor tightly bound to nuclus ionization nrgy incrass

6 Succssiv ionization nrgis I = 770 kj / mol n = Magnsium ( Z = 1 ) I1 = 78 kj / mol But why is I so much largr than I1 and I for th Mg atom? Th first two lctrons ar rmovd from th outr (valnc) shll But th third lctron is rmovd from an innr (cor) shll cor lctrons ar closr to th nuclus cor lctrons ar mor tightly bound to nuclus much mor nrgy rquird to rmov cor lctrons That is why Mg ion is not obsrvd I = 1450 kj / mol Elctron affinity -- th nrgy chang associatd with adding an lctron to an atom in th gasous stat Elctron affinity Exampl: Fluorin F(g) - Elctron affinity = F (g) 8 kj / mol E = 8 kj / mol sign is ngativ bcaus nrgy is rlasd (xothrmic procss) Elctron affinity masurs th as with which an atom gains an lctron Th mor ngativ th valu, th mor radily th atom gains an lctron Elctron affinitis (kj/mol) for th s- and p-block lmnts in th first fiv priods B Mg Ca - Sr -5 B -7 Al -4 Ga -0 In -0 C -1 Si -14 G -119 Sn -107 N P -7 As -78 Sb -10 O -141 S -00 S -195 T -190 F -8 Cl -49 Br -5 I -95 N X Priodic trnds for lctron affinity ar not as clar as thy ar for atomic radius and ionization nrgy. In gnral: Non-mtals hav high lctron affinity, mtals hav low lctron affinity