MolecularThermodynamics Quantum Part Atkins9e

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    7Quantum theory: introduction and principle

    Postulates of quantum mechanics:

    The wavefunction

    ψ   has all the information.

    ψ   can be obtained from the Schrodinger equation, ^ H ψ = Eψ  .

    The Born interpretation

    ⌈ ψ ⌉2  is the probability density for finding a particle.

    Acceptable wavefunctions

    ψ   must be continuous, a continuous first derivative, be single-valued, and be square-

    integrable.

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    Observables

    Ω → Ω̂   built from the position and momentum operators of the form

      ^ x= x ×   ̂p x=ℏid

    dx

    The eisenberg uncertainty principle

    [Ω̂1 , Ω̂2 ]=Ω̂1 Ω̂2−Ω̂2 Ω̂1≠0   ! ∆ Ω1 ∆ Ω2 ≥1

    2|⟨ [Ω̂1 , Ω̂2 ] ⟩|

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    8Quantum theory: techniques and applications

    Translational motion

    Free motion in one dimension

    −ℏ2

    2m

    d2

    ψ 

    d x2= Eψ 

    The solutions of this equation have the form

    ψ = A eikx +B e−ikx    E=k 

    2ℏ

    2

    2 m  where A and B  are constants.

    ! all values of "  are possible

    ! the translational energy of a free particle is not quanti#ed

    $n either case of eikx  or e−i kx , |ψ |2  is independent of % 

    ! the position of the particle is completely unpredictable

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    A particle in a box

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    (a) The acceptable solutions

    The Schrodinger equation for the region where &  ' ( is the same as for a free

    particle, so the general solutions are given as)

    ψ k = A eikx +B e−ikx= A (cos kx+isin kx )+B (coskx+isin kx )=( A+B ) coskx+ ( A−B ) isin kx

    Then, with new coefficients

    ψ k =C  coskx+ D sin kx E k =k 

    2ℏ

    2

    2 m

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    oundary conditions

    The wavefunction must be #ero where &  is infinite.

    ψ k  ( x )=0  for the regions of  x ≤ 0  and  x ≥ L

    ! by the requirement of wavefunction continuity 

    ψ k  (0)=0  and ψ k ( L)=0

    ! C =0  andkL=¿0

    ψ k  ( L )= Dsin¿

    !kL=nπ n=1,2,…

    ! ψ n ( x )= D sin(nπx/ L)n=1,2, …

    !  En=n2h2/8 m L2

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    !onclusion:

    The need to satisfy boundary conditions implies that only certain

    "a#efunctions are acceptable$ and hence restricts obser#ables to discrete

    #alues%

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    (b) &ormali'ation

    The normali#ation condition)

    ∫0

     L

    ψ ¿ψ d x=C 2∫0

     L

    sin2 nπx L

      d x=C 2 × L2=1 , so C =(

    2 L )

    1 /2

    The complete solution is

     En=  n

    2h

    2

    8m L2 n=1,2,…

    ψ n ( x )=(2

     L )1/2

    sin( nπx L  )

    The energies and wavefunctions are labeled with the *quantum number+ n .

    A quantum number is an integer in some cases, as we shall see, a half-integer

    that labels the state of the system.

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    c The properties of the solutions

    n   ↑  ! the number of nodes ↑  

    ψ n  has n  - nodes

    the number of nodes ↑  ! the average curvature of the wavefunction

    ! "inetic energy of the particle ↑

    /ach wavefunction is a superposition of momentum eigenfunctions)

    ψ n ( x )=( 2 L )1/2

    sin(nπx

     L  )=( 2 L )

    1

    2 ( eikx−e−i kx ) k =nπ  L

    ! equal probability of travel to both directions

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    Because n  cannot be #ero, the possible lowest energy is

     E1=  h

    2

    8 m L2

    This lowest, irremovable energy is called the 'eropoint enery.

    The physical origin of the #ero-point energy can be e%plained)

    . The uncertainty principle

    ! a confined particle some information for the position

    ! the momentum cannot be #ero precise value

    0. Acceptable wavefunctions

    ! must be #ero at both ends and need to be survived

    ! must have curvature

    ! non#ero "inetic energy 

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    The separation between ad1acent energy levels

     En+1− En=(n+1)2 h2

    8 m L2  −

      n2

    h2

    8 m L2=(2 n+1)

      h2

    8 m L2

    Separation ↓  as  L↑

    Separation → 0  as  L→ ∞  ! not quanti#ed li"e a free particle

    Separation ↓  as m↑

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    !orrespondin principle

    2lassical mechanics emerges from quantum mechanics as high quantum

    numbers are reached.

    (d) *rthoonality

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    3avefunctions corresponding to different energies are orthogonal)

    Suppose for two different energies of  En  and  Em

    ^

     H ψ n= En ψ n  ^

     H ψ m= Em ψ m

    Then ∫ψ m¿ ^ H ψ n d x= En∫ψ m

    ¿ψ n d x   ∫ψ n

    ¿ ^ H ψ m d x= Em∫ψ n¿

    ψ m d x

    4ow consider noting that energies are real

    ∫ψ m¿ ^ H ψ n d x−{∫ψ n¿ ^ H ψ md x }¿= En∫ψ m¿ ψ nd x− Em∫ψ nψ m¿ d x

    5sing hermiticity, the sum on the left is #ero, E

    (¿¿n− Em)∫ψ m¿ ψ n d x0=¿

    owever, the two energies are different6 therefore the integral on the right

    must be #ero)

    ∫ψ m¿ ψ n d x=0

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    +otion in t"o and more dimensions

    Schrodinger equation for a particle in a bo% in two dimensions)

    −ℏ2

    2 m (∂2ψ 

    ∂ x2 +

    ∂2ψ 

    ∂ 2 )= Eψ 

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    (a) ,eparation of #ariables

    ,eparation of #ariables technique

    7ivides the equation into two or more ordinary differential equations, one for

    each variable

    3rite the wavefunction as a product of functions)ψ ( x , )= ! ( x )" ( )

    3ith this substitution to the equation)

    −ℏ2

    2m

    d2 ! 

    d x2 = E !  !   

    −ℏ2

    2 m

    d2

    d 2 = E" "     E= E  ! + E" 

    ψ n1 ,n2 ( x , )=2

    ( L1 L2 )1 /2 sin(

    n1 πx

     L1)sin(

    n2 π

     L2)

     En1

    ,n2=( n1

    2

     L12+

    n22

     L22 )   h

    2

    8 m

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    $n same way, the solutions for a particle in a bo% in three dimensions)

    ψ n1 ,n2 ,n3 ( x , , # )=(8

     L1 L2 L3 )1/2

    sin(n1 πx

     L1)sin(

    n2 π

     L2)sin (

    n3 π#

     L3)

     En1

    ,n2

    , n3=( n1

    2

     L12+

    n22

     L22+

    n32

     L32 )   h

    2

    8 m

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    (b) -eeneracy

    3hen  L1= L2= L  in two-dimensional case6

    ψ n1 ,n2 ( x )=2 L sin (n

    1πx

     L   )sin (n

     L   )

     En1 ,n2=(n12+n2

    2)   h2

    8 m L2

    2onsider the cases n1=1,n2=2  and n1=2,n2=1 )

    ψ 1,2 ( x )=2

     Lsin(

    πx

     L  )sin(

    2 π

     L  )    E1,2=

      5h2

    8m L2

    ψ 2,1 ( x )= 2 Lsin (2 πx

     L  )sin( π

     L )    E2,1=   5h

    2

    8m L2

    ! Although the wavefunctions are different, they are deenerate.

    ! The occurrence of degeneracy is related to the symmetry of the system.

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    .ibrational motion

    armonic oscillation if the potential function is

    $ =1

    2 kx2

     with restoring force  % =−kx  from  % =−d$ /dx

    ! The Schrodinger equation becomes

    −ℏ2

    2 m

    d2

    ψ 

    d x2+

    1

    2kx

    2ψ = Eψ 

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    The enery le#els

    The permitted energy levels are

     E&=(&+ 12 )ℏ' '=( k m )1 /2

    &=0,1,2, …

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    armonic oscillator has #ero-point energy6

     E0=1

    2ℏ '

    ! Because the particle is confined, its position is not completely uncertain.

    ! Therefore, its momentum cannot be e%actly #ero.

    ! The particle fluctuates incessantly around its equilibrium position6 though

    classical mechanics would allow the particle to be perfectly still.

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    The "a#efunctions

    (a) The form of the "a#efunctions

    The wavefunctions for a harmonic oscillator,ψ ( x )= ( × (polynomial in x ) ×(bell-shaped Gaussian function )

    .   ψ → 0as x →) ∞

    0.   *heexp+nen 2 is proportional to x2× (mk )1 /2 , so it decays more rapidly for large masses

    and stiff springs.

    8.$t spread over wider range as& increases .

    ! 2orresponding principle wor"s at high & .

    ψ & ( x )= ( & H & (  )e− 2 /2

     = x- 

     - =( ℏ2

    mk  )1/4

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    /otational motion

    /otation in three dimensions: the particle on a sphere

    A particle of mass m  that is free to move anywhere on the surface of a sphere of

    radius r .

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    a The Schrodinger equation

    The Schrodinger equation is

    −ℏ

    2

    2 m   ∇2 ψ = Eψ 

    9rom :ustification ;.< on p8(

    1

    .2 /

    2ψ =

    −2mEℏ

    2  ψ /

    2=  1

    sin20

    ∂2

    ∂ϕ2+

      1

    sin0

    ∂0 sin 0

      ∂

    ∂ 0

     /2

    ψ =−   ψ ϵ ϵ=2 1E

    ℏ2

     2e3456e 1 =m. 2

    *7+854n5mn5m2e.6,9∧m9

    9=0,1,2, … m9=9 , 9-1,…, - 9 +1,- 9

    Angular momentum quantum number 9

    =agnetic quantum number m9

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    The normali#ed wavefunctions and energies are

    " 9, m9 (0 ,ϕ ) :spherical harmonics !able "#3 on p302$

     E=9 (9+1 ) :2

    2 1  9=0,1,2, …

    ! 854ni#ed∧independen +; m9

    ! (29+1 ) -foldde%enerate

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    (b) Anular momentum

    2omparing with the classical rotational energy,  E=ni5de +; 4n>594. m+men5m={9 (9+1 ) }1/2 : 9=0,1,2,…

    &-co mp+nen +; 4n>594.m+men5m=m9 : m9=9 ,9 -1,… , - 9

    The number of nodes in " 9, m9 (0 ,ϕ )  increases with 9

    ! higher angular momentum implies higher "inetic energy 

    ! a high "inetic energy arises from the motion parallel to the equator

    because curvature is greatest in that direction

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    (c) ,pace quanti'ation

    9or each 9 , there are only 29+1  possible m9  values)

    The orientation of a rotating body is quanti#ed) space quanti'ation

    The plane of rotation of a particle can ta"e only a discrete range of

    orientations.

    *tto ,tern and 0alther 1elach (in 2342)

    5xperiment: Shot a beam of silver atoms through an inhomogeneous

    magnetic field

    6dea: A rotating, charged body behaves li"e a magnet and interacts with the

    applied field

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    5xpectation:

    2lassical mechanics)

    Angular momentum can have all orientations)

    ! the associated magnet can ta"e any orientation

    ! a broad band of atoms is e%pected

    >uantum mechanics)

    The angular momentum is quanti#ed)

    ! the associated magnet lies in a number of discrete orientations

    ! several sharp bands of atoms are e%pected

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    /esults:

    *bser#ed discrete band$ and so confirmed the quantum mechanics%

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    (d) The #ector model

    9 x ,9   , and 9 #  are complementary observables)

    [ ̂9 x ,

    ^9  ]=i :

     ^9 #   [

     ^9  ,

    ^9 # ]=i :

     ^9 x   [

     ^9 # ,

    ^9 x ]=i :

     ^9 

    And

    [ 9̂2 ,9̂8 ]=0 8= x , , and #

    ! Although we can specify the magnitude of the angular momentum and any

    of its component, if 9 #  is "nown, then it is impossible to ascribe values to

    the other two components.

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    8%2 ,pin

    Stern and ?elach observed two bands of Ag atoms in e%periment)2onflict with the fact that 9  must be an integer.

    ! from spin , not due to orbital angular momentum

    ,pin:

    ,pin quantum number: 6

    +anitude: { 6 (6+1 ) }1/2ℏ

    ,pin manetic quantum number: m6=6 , 6 -1,… , -6

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    5lectrons ha#e spin:

    6=1

    2

    +anitude: {12 (

    12+1)}1 /2

    : =(34 )

    1/2

    :

    m6=+12

      (denoted as - or ↑ )

    m6=−12

      (denoted as ? or ↓ )

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    The ground state configuration of Ag atom)

    [ @. ] 4 d10 5 61 , a single unpaired electron outside a closed shell

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    Particles:

    Fermions: with half-integer spin

    /lectron, proton, neutron,@osons: with integer spin including (

    photon

    +atter is an assembly of fermions held toether by forces con#eyed by bosons%

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    3Atomic structure and atomic spectra

    The structure of hydroenic atoms

    amiltonian for hydrogenic atom

    ^ H =−ℏ2

    2 me∇e

    2−  ℏ

    2

    2m ( ∇ ( 

    2 −   e2

    4 π 0.

    (a) The separation of #ariables

    7ivide Schrodinger equation into two parts)

    .The motion of the atom as a whole

    0.The motion of electron relative to the nucleus

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    Schrodinger equation becomes)

    −ℏ2

    2 C  ∇2 ψ −

      A e2

    4 π 0 . ψ = E ψ 

     1

     C=

      1

    me+  1

    m (  C :.ed53edm466

    Because potential energy is centrosymmetric independent of angle,

    we can write

    ψ (. , 0 ,ϕ )= D (. ) " (0 ,ϕ)

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    The equation does separate, we have to solve

     /2

    " =−9 (9+1 ) " 

    spherical harmonics: 'uantum number 9 , m9  

    −ℏ2

    2 C

    d2

    5

    d .2+$ e;; 5= E55=.D

    7he.e $ e;; = − e2

    4 π 0. +

    9 (9+1 ) ℏ2

    2 .2

    ! a particle of mass    in one-dimensional region where the potential

    energy is &eff  ) radial "a#e equation

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    b The radial solutions

    $ e;; =− e2

    4 π B0 .+

    9 (9+1 )ℏ2

    2 .2

    The st term)

    2oulomb potential energy 

    The 0nd term)

    stems from centrifugal force from the angular momentum of electron

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    $ e;; = − e2

    4 π 0 .+

    9 (9+1 ) ℏ2

    2 .2

    0hen 9=0

    /lectron has no angular momentum

    ure 2oulombic and attractive at all radii

    0hen 9 ≠ 0

    The centrifugal term is positive repulsive

    As . →0 , this repulsive term dominates the 2oulombic term.

    ! $ e;;   is repulsive

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    The allowed energies

     En=  − 2  e4

    32 π 2

    B 02ℏ

    2n

    2 n=1,2,…

    adial wavefunctions have the form D ( . )=( polynomial in . ) ×(decayin% e(ponential in . )

    adial wavefunctions depend on both n  and 9

     Dn, 9 (. )= ( n, 9 9 Ln+1

    2 9+1 (  ) e−  /2

    7he.e =2 A.

    n 4040=

    4 π 0ℏ2

    me e2  =52#" pm(B+h. .4di56)

     L (  ):466+3i4ed L4>5e..e p+9n+mi49

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    6nterpretation of the radial "a#efunction$  D (. ) :

    ./%ponential factor ensures that  D (. )→0  as . →∞ .

    0.The factor 

    9

     ensures that provided9>0

     D ( . )=0

     at the nucleus.8.   L (  )  oscillates and accounts for the presence of radial nodes.

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    3%2 Atomic orbitals and their eneries

    Atomic orbital:A one-electron wavefunction for an electron in an atom

    7efined by three quantum numbers) n , 9 , m9

      ψ n , 9 , m9 F|n , 9 , m9 ⟩

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    >uantum numbers)

    rincipal quantum number) n

    n=1,2,3, …

     Dee.minehe ene.> +; 4 hd.+>eni34+m

     En=  − 2  e4

    32π 2

    02

    ℏ2

    n2

    Angular momentum quantum number) 9

    9=0,1,2,… , n−1

     =4>ni5de +; 4n>594. m+men5m={9 (9+1 ) }1/2ℏ  

    =agnetic quantum number) m9

    m9=−9 ,−9+1,… ,9−1, 9

    &-co mp+nen +; 4n>594. m+men5m=m9 ℏ

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    The value of the principal quantum number, n ,

    controls the ma%imum value of 9  

      9

     controls the range of values ofm

    9

    /lectron has its own spin) 6=1

    2m6=)

    1

    2

    ! 4eed four quantum numbers (n , 9 , m9 , m6)  to specify

    the state of an electron in a hydro)enic atom 

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    (a) The enery le#els

    /nergy levels of hydrogenic atoms) En=

      − 2  e4

    32 π 2

    B 02ℏ

    2n

    2

    2+5nd 64e6 : E0 → n+854ni#ed )

     E ∝  2

    ydberg constant)

    h3 D H =

       H  e4

    32 π 2 02 ℏ2  H i6 he .ed53ed m466 ;+. hd.+>enG

     D H =−  H 

    me D D=

      me e4

    8 π 2

    02

    h3

    3

    ! The only discrepancies arise from the neglect of relativistic corrections

    the increase of mass with speed.

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    (b) Atomic orbitals

    The ground state) ψ 1,0,0 F|1,0,0 ⟩

    ψ =1

    (π 403 )1 /2 e−. /40(;+.  =1)

    1 6 +.2i49 i6 6phe.i3499 6mme.i349G

    m4xim5m495e+; ψ =1

    (π 403 )1/2

    (4 .=0)∧exp+neni499 de346

    2ontributions of the potential and "inetic energy 

    otential energy prefers to sit on the top of the nucleus.

    Cinetic energy li"es to be spread out uniformly.

    ! A compromise between the two e%tremes)

    ! The wavefunction spread away from the nucleus and has a reasonably

    low average curvature.

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    3%4 ,pectroscopic transitions and selection rules

    Transition

    ψ i → ψ  I ∆ E=h J

    ,election rule) a statement about which transitions are allowed

    *allowed+ or *forbidden+

     !onser#ation of anular momentum:

    A photon has an intrinsic spin angular momentum) 6=1 .

    ! ∆ 9=) 1 ;+.he .4n6ii+n +; ψ i → ψ  I

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     Quantum mechanical #ie": (ustification 2%9 on p;)

      #, ;i=∫ψ ; ¿  # ψ i d x=⟨ ; |  #|i ⟩;+. +ne - e9e3.+n4+m

     =−e . )ith components:     x=−e x , =−e ,  #=−e#

    After calculating  ;i  for all three components

    !  ;i ≠ 0 )hen∆ 9=) 1∧∆ m9=0,) 1

    ! 4o restrictions for n , because it does not relate directly to angular

    momentum

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    1rotrian diaram:

    Summari#es the energies of the states and the transitions between them

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    The structures of manyelectron atoms

    The Schrodinger equation for a many-electron atom is highly complicated and no

    analytical e%pression for the orbitals and energies can be given.

    ! 3e are forced to ma"e appro%imations.

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    Pauli principle:

    3hen the labels of any two identical fermions are e%changed, the total

    wavefunction changes sign6 when the labels of any two identical bosons are

    e%changed, the total wavefunction retains the same sign.

    auli principle for two-electron total wavefunction) K  (1,2 )

    K  (2,1 )=−K  (1,2 )

    9or two electrons, there are four possible spin states)

    - (1 ) - (2)- (1) ?(2) ? (1)- (2) ? (1) ? (2)

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    Because we cannot tell which electron is which or there must be symmetry

    −¿(1,2) ? (1) ? (2)+¿(1,2) ¿

    - (1 )- (2) ¿

    3here  ) (1,2)=(1/2)1 /2 {- (1 ) ? (2)) ?(1)- (2)}

    −¿(1,2)−¿ (2,1)=− ¿+¿ (1,2 )  ¿+¿ (2,1 )= ¿

     ¿

    9our possible total wavefunctions for the same special function ψ  )

    ψ (1 ) ψ (2)-  (1 ) - (2)

    ψ (1 ) ψ (2) ? (1) ? (2)

    +¿ψ (1 ) ψ (2) ¿

    −¿ψ (1 ) ψ (2) ¿

    ! Only the last one satisfies the auli principle.

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    Any acceptable wavefunction for closedshell species)

    ,later determinant form:

    K  (1,2,… , ( )= 1( ( M )1/2

    [ψ 4 (1) - (1 )   ⋯   ψ 4 ( ( ) - ( ( )

    ⋮ ⋱ ⋮

    ψ  # (1) - (1 )   ⋯   ψ  # ( ( ) - ( ( ) ]! Antisymmetric under any e%change of any pair of electrons

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    (a) Penetration and shieldin

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    5ffecti#e nuclear chare:

     e;; = − 

    7he.e i6he 6hie9din>3+n64n 

    The shielding constant is different for 6  and  p  electrons.6  electron has a greater penetration than a  p  electron.9ig (.0( on

    p8D(

    6  electron has less shielding than a  p  electron.

    ! The energies of subshells depend on 9 , but not on m9  

    6

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    .alence electrons:

    /lectrons in the outermost shell of an atom in its ground state

    ! esponsible for the chemical bonds that the atom forms

    (b) The buildinup principle

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    Building-up principle or Aufbau principle )

    9or an atom with atom number   )

    9eed into the orbitals the    electrons in succession.

    The order of occupation is)

    1 62 6 2 p 3 63 p 4 63 d 4 p 5 6 4 d * 6

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    und+s ma%imum multiplicity rule)

    An atom in its ground state adopts a configuration with the greatest number

    of unpaired electrons

    Spin correlation)

    /lectrons with parallel spins behave as if they have a tendency to stay well

    apart, and hence repel each other less.

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    2onsider to satisfy the auli principle

    +¿(1,2) 4(1,2)−¿(1,2)  p(1,2)K 2(1,2)=ψ ¿

    K 1(1,2)=ψ ¿

    7he.e ψ ) (1,2 )=(1/2 )1/2 {ψ 4 (1) ψ 2(2))ψ 2 (1 ) ψ 4(2) }

      p (1,2 )   is parallel spin state

     4 (1,2)  is paired spin state

    3hen two electrons occupy at the same position, .1=.2 :

    −¿ψ ¿

     vanishes while +¿ψ ¿  survives

    −¿ (1,2)=(1/2 )1 /2

    {ψ 4 (1 )ψ 2 (2 )−ψ 2 (1 )ψ 4(2)}ψ ¿

    ! spin correlation

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    5lectron confiurations:

    On average, 3 d  electrons are closer to nucleus than 4 6  electrons.

    ! 3 d  electrons repel each other more strongly than the two 4 6  

    electrons.

    ! Sc has [ A. ] 3 d1 4 62

    2r and 2u have [ A. ] 3 d5 4 61  and [ A. ] 3 d10 4 61 , respectively.

    The subtle shades of energy differences and electron-electron repulsion

    ! The rich-comple%ity of inorganic d- me49  chemistry 

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    2alculations show that the energy difference between [ A. ] 3 d3  and

    [ A. ] 3 d1 4 62  depends on  e;; 

    ! As A e;;   increases, transfer of a 4 6  electron to a 3 d  orbital becomes

    more favorable because electron-electron repulsions are compensated

    by attractive interactions.

    !2+¿ : [ A. ] 3d3

    $ ¿ , the observed [ A. ] 4 60 3 dn  configurations for

    2+¿ = 

    ¿  cations of

    Sc through En

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    The spectra of complex atoms

    The actual energy levels are not given solely by the energies of the orbitals,

    because the electrons interact with one another in various ways.

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    3% ,inlet and triplet states

    ,inlet:

    −¿ (1,2)=(1/2 )1 /2 {- (1 ) ? (2 )− ?(1)- (2)} ¿

    Triplet:

    - (1 ) - (2 )

    +¿ (1,2)=(1

    2 )1

    2 {- (1 ) ? (2 )+ ? (1 )-  (2 ) } ¿

     ? (1) ? (2)

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    9or states arising from the same configuration, the triplet state is generally lies

    lower than the singlet state. The two states of 1 61 2 61 He  differ by FD0 cm- 

    corresponding to (.G e&.

    T"o simple features in the spectrum of atomic

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    3%9 ,pinorbit couplin

    ,pinorbit couplin:

    $nteraction of the spin magnet moment with the magnetic field arising from the

    orbital angular momentum

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    (a) The total anular momentum

    The energies of the levels with quantum numbers 6 , 9 , I )

     E9 , 6 , I=1

    2

    h3A { I ( I+1 )−9 (9+1 )−6 ( 6+1 ) }

    The strength of the spin-orbit coupling depends on the nuclear charge.

    ! The greater the nuclear charge, the stronger the spin-orbit interaction.

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    (b) Fine structure

    Fine structure:

    The structure in a spectrum due to spin-orbit coupling

    $n 4a, the spin-orbit coupling affects the energies by about < cm-

     

    3%;Term symbols and selection rules

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    a The total orbital angular momentum

    b The multiplicity 

    c The total angular momentum

    Term symbol:

     L❑2 N+1

    594. m+men5m854n5mn5m2e. , L

    m4>ni5de: { L ( L+1 ) }1 /2ℏ

    495e : L=91 +92 ,9 1 +92−1,… ,∨91−92∨¿ L=012345* …

     L=N OD %P H 1 …

    4 39+6ed 6he99h46 4 #e.+ +.2i49 4n>594. m+men5mG

    +496pin 854n5m n5m2e. , N

    495e : N=61+62, 61+62−1,… ,∨61−62∨¿

    m59ip9i3i=2 N+1

    +494n>594. m+men5m 854n5mn5m2e. , 63heme :

    f the spin-orbit couplin% is )ea, then it is effectie

    only )hen all the orbital momenta are operatin% cooperatiely

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    495e :

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     == couplin

    ussell-Saunders coupling fails when the spin-orbit coupling is large in

    heavy atoms. $n that case, the individual spin and orbital momenta of the

    electrons are coupled into individual 1 values6 then these momenta are

    combined into a grand total : .

    !orrelation diaram )

    The labels derived by using the ussell-Saunders scheme can be used to

    label the states of the 11 -coupling scheme.

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    (d) ,election rules

    ,election rules:

    ∆ N=0 ∆ L=0,) 1 ∆9=)1 ∆ 2e3+me6 m+.e4pp.+p.i4e

    ! .4n6ii+n62e7een 6in>9e ∧.ip9e 64e6 (;+. 7hi3h∆ N=)1 ) ,

    7hi9e;+.2idden∈9i>h 4+m6, 4.e499+7ed∈he4 4+m6G

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