Atomic Structure

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Transcript of Atomic Structure
Chemistry 285Advanced Inorganic
Chemistry
Lecture Notes
Assoc. Prof. Joel R. Salazar
Chapter 1
Atomic Structure
Common Applications of Inorganic Chemistry
How about many electron system?
Polyelectronic Atom
Semiempirical Method and Ab –initio Approximations : Hartree Fock Method (SCF) Assumptions1.) one reasonable φ for each electron2.) shielding or screeningNote: these assumptions are used to explain periodic
properties:a.) radius b.) electron affinity c.) ionization energy d.) electronegativity
Hartree – Fock SCF Orbitals Iterative method for solving the manyelectron
Schrödinger equation
developed by D.R. Hartree (1928)
Effective Nuclear Charge
Sample Problem
What is the Zeff for P15
Ans: Zeff = 4.8
Sample Problem
2.) Calculate the Ionization energy for 13 Al.
13Al =1s2 (2s2p)8 3s23p1
Ans. 10.73 Kj
Solution
Alo = 1s2 (2s2p)8 (3s2 3po) = 2(0.35) + 8 (0.85) +2 (1.0) = 9.5
Al+ = 1s2 (2s2p)8 (3s1 ) = 1(0.35) + 8 (0.85) + 2(1.0) = 9.15
B.E. = 13.6 (Z –δ/n)2
B.E.Al (o) = 3 (13.6) (13 – 9.5/3)2 = 55.53
B.E.Al(+) = 2 (13.6) (13 – 9.15/3)2 = 44.80
I.E. = B.E. (Alo)  B.E.(Al+) = 10.73 Kj
What is the Zeff for Nickel
3d and 4s
3d = 7.55
4s = 4.05
Atomic Energy States
Term symbols: a shorthand notation that describes the electron distribution in atoms or ions, i.e. the ml and ms quantum numbers. Spectroscopists most frequently use these.
Microstate = defined as the different ways of putting the electrons in orbitals while taking into account the electron –electron repulsion
The result of calculation is called Russell –Saunders coupling and presented as an atomic term symbol
Spin orbit Coupling = the spin and orbital angular momenta of individual electrons are strongly coupled together
The possible term symbols for various electron configurationElectron Configuration Term Symbol
s1 2S (2)
p1 2P (6)
p2 and p4 1S,1D,3P (15)
p3 2P,2D, 4S (20)
p1 and p5 2P (6)
d1 andd9 2D (10)
d2 and d8 1S,1D,1G,3P,3F (45)
d3 and d7 2P,2D,2F,2G,2H,4P,4F
d4 and d6
d5
Terms for Equivalent electrons
Terms for configuration
P6n is the same as pn (p4 and p2; p1 and p5; p3
and p6)
D10n is the same as dn ( d1 and d9, d2 and d8 etc.)
Term Symbols for nd2
Term Number of State
1G 9x1 =9
3F 7x3 =21
1D 5x1 =5
3P 3x3 =9
1S 1x1 =1
Total =45 (microstates)
Multiplicity
s1 l = 0 and s = ½
Term Symbol : 2S
2S +1 = 2(1/2) + 1 =2
p1 l =1 and s = ½
2S + 1 = 2 (1/2) + 1 = 2
Term Symbol : 2P
s1p1 parallel (3P)and antiparallel (1P)
Microstates (d2)
1.) ‖ _ _ _ _ L = 4 1G
2.) I I _ _ _ L = 3 3F
3.) _ ‖ _ _ _ L = 2 1D
4.) _ I I _ _ L = 1 3P
5.) _ _ ‖ _ _ L = 0 1S
What is the ground term of the configurations 3d5 of Mn2+ and 3d3 of Cr3+
Ans. 6S and 4F
The ML and Ms are tabulated in array
2 11 1 2 1
ML 0 1 3 11 1 2 12 1
1 0 +1MS
Highest ML = 2 (the array ML = 2,1,0,1,2 exists
corresponding to L = 2)These values occur for Ms = 0A term with L = 2; S = 0 or1D
Term Symbols
The array after subtracting the microstate 1D2
1 1 1 1
Ml 0 0 1 2 11 1 1 12
1 0 1
Ms
From the highest remaining ML = 1
The array ML = 1, 0, +1+ exists corresponding to L =1
These values occur for Ms = 1, 0 ,1L = 1; and S = 1 or 3P
Term Symbols
The array after subtracting the microstate 3P
2
1
Ml 0 1
1
2
1 0 1
Ms
Ml =0 and MS = 0 and 1S
Sample Problem
Use Hund’s rules to deduce the lowest energy state of an excited state of a Be atom whose electron configuration is 1s2 2s1 3s1 and of the ground state of a carbon atom 1s22s22p2
Ans: 3S1
3Po
Sample Problem
Identifying Ground State
3d2 Ans. 3F2
3d5 Ans. 6S5/2
3d8 Ans. 3F4
Sample problem
Show that the term symbol corresponding to an nd10
electron configuration is 1So
Note : Same as ns2 and np6
Sample Problem
Deduce the values of J associated with the term symbols 2S, 3D and 4F.
Problem Set 1
1.) a.) Determine the number of microstates associated with electron configuration p1d1
b.) Find out all the term symbols for this electron configuration
The Periodic Table
Lanthanide contraction
Note that although there is a significant increase in radius in going from the 3d to the 4d metals, the 4d and 5d metals are remarkably similar in size – a result of Lanthanide contraction
Electron Affinity = the energy change associated with the process in which the electron is added to a gaseous atom.
A(g) + e ==== A(g)
Measuring Electronegativity
1.) Mulliken ElectronegativityAssumption:
if the atoms I and EA are both low, then the atom will tend to lose electrons than gain them
χM = 1/2 (I + EA)Conversion between Pauling and Mulliken electronegativity
χP = 1.35 (χM)1/2 – 1.372.) Allred –Rochow DefinitionAssumption: Elements with high electronegativity are those with high
effective nuclear charge and with smaller covalent radius
χAR = 0.744 + 35.90 Zeff/ (r/pm)2
Polarizability (α)
Polarizability of an atom is its ability to be distorted by an electric field( such as that of the neighboring ion)
A polarizable atom or ion is one with orbitals that lie close in energy
Polarizability is likely to be high if the separation of the frontier orbitals is small
Large, heavy atoms and ions tend to be highly polarizable (closely separated frontier orbital)
Sample Problem
Which would be the more polarizable: an F an I ion?
Which would be more polarizing, Na+ or Cs+?Species that effectively distort the electron distribution of a neighboring atom or anion are described as having polarizing ability.
Fajans Rule (factors that affect polarization)1.) Small, highly charged cations have polarizing ability2.) Large, highly charged anions are easily polarized3.) Cations that do not have a noble –gas electron configuration are
easily polarized (important for d –block element)