Periodicity & Many-Electron Atoms

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1 Chap. 8 ELECTRON CONFIGURAT N & CEMICAL PERIODICITY Periodicity & Many-Electron Atoms Understand the correlation of electron configuration and the periodic character of atomic properties such as size, ionization energy, and electron affinity Recognize the periodicity of the classification of metals, metalloids, and nonmetals Use electron configuration to predict common chemical and physical properties of the maingroup or representative elements [D. I. Mendeleev] Similar chemical and physical properties recur periodically when elements arranged by atomic mass (now, atomic number) [G. N. Lewis] Chemical behavior is related to electron configuration Electrons generate magnetic fields characteristic of spinning charges: there is a fourth quantum number (spin, m s = +½ or ½) e - e - Many-Electron Atoms: Characteristics [W. Pauli] No 2 electrons can have the same set of 4 quantum numbers (EXCLUSION PRINCIPLE) n = 3 4s 3p Electrostatic and spin interactions cause sublevels to have different energies PENETRATION: Within a level, near-nuclear electron densities affect relative energies of orbitals (s < p < d < f) Energy n = 2 NUCLEAR CARGE (): higher nuclear charge lowers orbital energies n = 1 SIELDING: Inner-orbit electrons shield outer-orbit electrons from nucleus ( = eff ) Penetration: Nuclear charge and shielding: n = 1 n = 2 n = 3 Outer-electron shells expand with increasing innerelectron screening electrons penetrate closer to nucleus than electrons Penetration decreases shielding by electrons, lowering electrons energy relative to that of electrons = 2 = 10 = 18 Inner-electron shells contract with increasing nuclear charge Page 8-1

2 8.3 Quantum-Mechanical Model & Periodicity AUFBAU (Construction) PRINCIPLE: The process of adding electrons to build up an atom s electron configuration [Bohr, Pauli, et al.] = ground-state configuration Orbitals are filled with pairs of electrons having anti-parallel spins ( = different m s ) Energy n = 3 n = 2 4s 3p UNDS RULE: Filling orbitals of equal energy, maximize the number of electrons with parallel spins (same m s ) = unpaired electrons n = 1 Electron configurations relate to to the patterns of of chemical behavior for the elements 2 3 Be 4 B 5 C 6 N 7 O 8 F Orbital Diagram e [] p 6 4s p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 See Fig 8.4 p 243 s Within Groups Elements (especially main-group elements) have similar outer electron configurations Elements within a group have similar chemical properties Among main-group elements, the group number = the number of outer electrons O S 2 2 3p 3p 4 4 Se Se 4s 4s 2 2 4p 4p 4 4 Te Te 5s 5s 2 2 5p 5p 4 4 Po Po 6s 6s 2 2 6p 6p p 3p 6 6 r r 4s 4s 2 2 4p 4p 6 6 Xe 5s 5s 2 2 5p 5p 6 6 Rn Rn 6s 6s 2 2 6p 6p 6 6 Categories of Electrons INNER (Core) ELECTRONS: Electrons in filled lower energy levels, closest to nucleus OUTER ELECTRONS: Electrons in the highest energy level, farthest from nucleus Similar outer electron configurations within a group C Si Ge Core Valence [] 2 2 [] 2 3p 2 [] 4s p 2 VALENCE ELECTRONS: Electrons involved in the formation of chemical bonds Main-group elements = outer electrons Transition elements = includes (n 1)d electrons Chemical and physical behavior is is determined by by the number and type(s) of of valence electrons Page 8-2

3 1A 1A 1 2A 2 Main- Group 3 3B 4 5 s block 6 7 4B 5B 6B 7B 8B 1B Transition Metals dd block block 3A 4A 5A 7A Main-Group pp block block 1 2A 2 3 3B 4 4s 5 5s 6 7 6s 7s 7s 4B 5B 6B 7B 8B 1B 4d 5d 5d 6d 6d 3A 4A 5A 7A 3p 3p 4p 4p 5p 5p 6p 6p Lanthanides (Rare-Earth Metals) ff block block Actinides ff block block 4f 4f 5f 5f Fun exceptions to what Schloman just told you: V Cr Mn Ni Cu Core Valence [] 4s 2 3 [] 4s 1 5 [] 4s 2 5 [] 4s 2 8 [] 4s 1 10 n [] 4s Trends in Atomic Properties ATOMIC SIE r = ½d Cu-Cu r = ½d Cl-Cl IONIATION ENERGY M(g) M + (g) + e E = IE 1, IE 1 > 0 M + (g) M (g) + e E = IE 2, IE 2 >> IE 1 ELECTRON AFFINITY (EA) X(g) + e X (g) E = EA 1 L = r Cl-Cl + r C-C Atomic Size Within group: Atomic radius tends to increase from top to bottom ( ) 200 Within period: Atomic radius tends to decrease from left to right ( ) Function of outermost occupied n and eff (core electron shielding) r, pm r Be Ca B C N O F Al Si P S Cl Ga Ge As Se Br r Page 8-3

4 Ionization Energy Ionization Energy, kj/mol Energy required to remove an electron from ground-state atom Within a group, IE 1 tends to decrease from top to bottom ( ) Within a period, IE 1 tends to increase with eff ( ) IE inner-shell >> IE outer-shell I 1, kj/mol X X + + e - r IE 1 IE 2 IE 3 IE 4 IE Al Si An An atom s inner-shell (core) electrons are too tightly bound to to its its nucleus to to be be either lost or or shared with another atom Electron Affinities 8.5 Atomic Structure & Chemical Reactivity Energy change when an electron is added to an atom Reactive nonmetals (groups, 7A) readily form stable anions (EA << -100) Reactive metals (group 1A) preferentially form cations (-100 < EA 0) Elements with filled sublevels (group ) unreactive (EA 0) EA, kj/mol Be X + e - X - F Cl Be Ca Sc Rb Sr Y Cs Ba La Fr Ra Ac INCREASING NONMETALLIC CARACTER (tendency to GAIN electrons) Ti V Cr Mn r Nb Mo Tc f Ta W Re Ce Pr Nd Th Pa U Fe Co Ni Ru Rh Pd Os Ir Pt Pm Sm Eu Np Pu Am Gd Cm Cu Ag Au Tb Bk n Cd g B C N Al Si P Ga Ge As In Sn Sb Tl Pb Bi Dy o Er Cf Es Fm Tm Yb Lu Md No Lw O F S Cl Se Br r Te I Xe Po At Rn INCREASING METALLIC CARACTER (tendency to LOSE electrons) 1A METALS Form cations isoelectronic with nearest noble gas Form cations in 2 O Oxides: ionic, act as bases in water NONMETALS Form anions isoelectronic with nearest noble gas Form anions, oxyanions in 2 O Oxides: covalent, act as acids in water NOTE: Metalloids, weak metals (Al) form amphoteric oxides that can act as acids or bases O S 2 2 3p 3p 4 4 Se Se 4s 4s 2 2 4p 4p 4 4 7A F +2e e Cl Cl +2e +1e 2 2 3p 3p p 3p 6 6 Br Br +2e +1e 4s 4s 2 2 4p 4p 5 5 4s 4s 2 2 4p 4p 6 6 I 2 2 r r Xe +1e 5s 5s 2 2 5p 5p 5 5 5s 5s 2 2 5p 5p 6 6 2e 2A [] [] 1 1 [] [] 1 1 [] [] 2 2 []4s []4s 1 1 []4s []4s 2 2 Rb Rb [r]5s [r]5s 1 1 Cs Cs Ca Ca Sr Sr [r]5s [r]5s 2 2 Ba Ba [Xe]6s [Xe]6s 1 1 [Xe]6s [Xe]6s 2 2 Page 8-4

5 Monatomic Ions Main-group elements form ions isoelectronic with the nearest noble gas (±3 e ) Transition metal ions rarely have a noble gas configuration 1-1A 1 2A 2 3A 4A 5A A 1- Transition metal ions with unpaired electrons exhibit paramagnetism attraction to an external magnetic field (Cr 3+ ) Transition metal ions with paired electrons exhibit diamagnetism no attraction to (or slight repulsion by) an external magnetic field (La 3+ ) 3 3B B 5B 6B 7B 3+ 8B 3+ 1B Ion Size Cations are smaller than their parent atoms Anions are larger than their parent atoms For ISOELECTRONIC IONS (ions with equal numbers of electrons), size decreases with increasing nuclear charge M M + + Rb + + Rb + X X - F F - Cl Cl - Br Br - I I - Cs Cs + Page 8-5