Download Topics • Introduction to Transition Metals • Molecular Structure and

Topics
• Introduction to Transition Metals
– Chapters 1 and 19
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Molecular Structure and Bonding
Molecular Symmetry
Molecular Orbital Theory
Coordination Complexes
Electronic Spectra of Complexes
Reactions of Metal Complexes
Organometallic Chemistry
Introduction
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Transition Metals
Discovery of the Transition Metals
Atomic Structure
Periodicity
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Transition Metals
• Defined as:
– strictly: those elements having partly filled d or f
shells
– more broadly: those elements having partly filled d
or f shells in any of their common oxidation states
• allows us to include Cu, Ag, Au
– eg. Cu2+: 3d9
Characteristics
• Physical
– metals
• ductile, malleable, conducting
– hard, strong, high-melting, high-boiling, thermally conductive
– form alloys
• Chemical
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largely electropositive
variable oxidation states
typically highly coloured ions or complexes
paramagnetic compounds
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The Sub Groups
• There are three main groups of transition
metals
– d-block (aka main transition group)
• 21-29
• 39-47
• (57) 72-79
• (89)104-111
– lanthanides
• (57) 58-71
– actinides
• (89)90-103
Actually that is a little too neat:
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Sc and Y are very similar to the lanthanides
lanthanides are all very similar to each other
third row starting with Hf are mostly d like
actinides are a mess
– 6d and 5f are very similar in energy
– actinides may contain a mixture of 6d and 5f
electrons
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However, we are going with it
• in general
Group
Frontier Orbitals
d block
3d, 4d, 5d
lanthanides
4f
actinides
5f
History of the Transition Metals
• Transition metals were some of the first recognized
as elements:
– Au, Ag, Cu, Fe
• Alchemists (1000 BC-1700 AD)
– Pt, Zn
• Chemical Extraction (1700-1900 AD)
– Co, Ni, Mn, Mo, W, Zr, U, Ti, Y, Cr, Nb, Ta, Pd, Os, Rh, Ir
lanthanides
• Instrumental Identification (1860-1925)
– Cs, Rb, Tl, In, Ga, Ho, Pr, Nd, Ac, Pa, Hf
• Synthetic Elements (1937-1961)
– Tc, Np, Pu, Pm, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr
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Our Focus
• We will focus on the d transition metals, their
electronic structure, bonding and complexes
• Primarily looking at on the 3d with
investigations of how 4d and 5d metals differ
• But first we need some tools:
– Quantum review
– Symmetry
– Bonding – valence bond, molecular orbital theory
Quantum Review
• Chemistry is dominated by behaviour of electrons
• Cannot understand electrons without quantum
theory
• Essentials:
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Bohr Model: quantized energy levels
De Broglie: wavenature of electrons
Heisenberg: uncertainty and probability -> orbitals
Schrodinger: wave equation -> quantum numbers
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Quantum Review: Bohr
• energy of a free electron can be of any value
• Bohr proposed a quantized solution to the
line spectra of gaseous H atoms
• energy of an electron bounded by its
attraction to a nucleus is limited to certain
values, aka quantized
– i.e. values of E that solve the equation are
dependent on n, the principal quantum number
2π 2 me 4
En = −
n2h
Quantum review: de Broglie and Heisenberg
• Enter the waves and the uncertainty….
• Wave-particle duality of electrons proposed
– Relates momentum and velocity to a wavelength
– Causes problems for knowing exact location and
velocity of the electron
• Solution: don’t care about the exact position
and velocity but only the volume it is likely to
be found in
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Quantum Review: Schrödinger
Hˆ ψ = Eψ
• The Schrödinger equation gives us the
necessary relation between the boundary
conditions and the energy levels for an
electron
• Solving the Schrödinger equation means
finding the permissible energy levels and
identifying the wavefunction (ψ) which
describes the electron
Bonding and Wavefunctions
• when two wavefunctions
share space (aka overlap)
they can interfere
– constructive interference
• increases the probability
of an electron being found
in the overlapping area
– destructive interference
• decreases the probability
of an electron being found
in the overlapping area
– Will return to this idea for
forming bonds
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Polar Coordinates and Probability
• electrons are described by a wavefunction (ψ)
– This is the function which provides a solution to
the Schrodinger Equation
– In 3-dimensions this becomes unwieldy
– Use polar coordinates to express wavefunction in
terms of radial and angular components
– Wavefunctions are dependent on certain
incremental integers aka quantum numbers
• typically interested in the probability (ψ2) of an
electron being found within a certain region in
space
Quantum Review: the Numbers
Quantum
number
Label
Value
Designates
n
Principal
1,2,3…
Overall size
l
Azimuth
quantum
number
Magnetic
quantum
number
Spin
magnetic
number
0,1,2…n-1
a.k.a. s,p,d,f
Orbitals, also
nodal
surfaces
Multiplicity of
orbitals
ml
ms
l,l-1,l-2…-l
2l+1
+½, -½
Capacity of
orbital
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Radial Distribution Functions
• using polar coordinates allows for simple
representation of ψ
– R = radial wavefunction
– A = angular wavefunction
• the radial distribution function is most useful
to us
– allows us to graphical display the probability of
finding an electron within a certain radius from the
nucleus
– allows us to draw the orbitals that we know and
love
s and p Orbitals
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d Orbitals
f Orbitals
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Aufbau Principle
• 1s, 2s, 2p, 3s, 3p, 4s .....
• 3d, 4p, 5s, 4d, 5p, 6s ....
• 5d1 , 4f , 5d2-10
• Energy level of electrons quickly becomes
more than just dependent on n
• why?
Nuclear Shielding
• energies of the electron levels in multielectron atoms
are dependent on the populations of all the other
levels
• shielding of the nuclear charge by inner electrons
reduces the nuclear attraction experienced by a
valence electron
• result is a reduced effective nuclear charge (Zeff)
• degree to which the nuclear charge is shielded
depends on shape (penetration) of the particular
orbital
– s is highly penetrating (large volume near the nucleus)
– p less penetrating (smaller volume near the nucleus)
– Highly penetrating orbital means less shielding, higher
attraction, lower Energy (I.e. energy of 2s is lower than 2p)
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Half Shells
• an additional complication
• energy levels can be subtly altered by
forming half filled shells
– i.e. s2d9 configuration is higher energy than s1d10
– see Cu, Ag, Au
• what is the electron configuration of Mo?
Periodicity of the Elements
• atomic and ionic radii
– lanthanide contraction
• ionization energy
• electron affinity
• electronegativity
– Pauling, Mulliken, Allred-Rochow
• Polarizability
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