Transcript SOLUTIONS AND THEIR BEHAVIOR

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CHAPTER 22
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Chapter 22 Overview
• A brief overview of producing Iron and
Copper metal
• The bulk of our time will be spent
dealing with one of the more interesting
features of transition metals in
particular why do transition metals
produce the vibrant colors we normally
see but don’t think about
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Transition Metals and Color
• Main Group metals are All Color-Less i.e.
Sodium, Magnesium, Aluminum, Lead, etc…
are ALL white solids (sulfur compounds
excluded)
• So why is it that Transition Metal
compounds have color
• We need to examine the key difference
between Main Group and TM and that has
to do with the TM’s unique d-orbitals only
to understand how color is possible
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Uranium glass is
the only kind of
glass which can
be bound directly
to metal once the
glass is heated; it
is useful for
making glassmetal objects
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Now for some ground work
• Our focus is mainly on the 3d metals, these tend to be the most reactive the
therefore the most commonly encountered and studied
• General Properties of TM
– Electron Configurations
– Oxidation Numbers
– Radii
– Density
– Mp
– Magnetism
• How to make Fe and Cu
PROPERTIES OF THE TRANSITION
ELEMENTS
Electron Configurations
• The most significant factor in the
behavior of these elements is the
electronic configuration.
• The d-group elements have an ns (n1)d configuration. The number of delectrons is the most important.
• As ions form, the s-electrons are lost
first giving a "d" configuration for the
ion, ie. d5, d8, etc.
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PROPERTIES OF THE TRANSITION
ELEMENTS
Sulfides phosphates and oxides are most
common.
• The 5f elements are generally not naturally
occurring since they are unstable
• The densest elements are Os and Ir due to
the Lanthanide contraction (shielding effect
of f-block elements not effective).
• Some of these elements are quite toxic and
are called "heavy-metals".
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Lanthanide Contraction
• Z* applies the same for successive elements
across the f-block as it does in any other
period.
• Shielding effects diminish across the period
due to an increase in the number of protons.
• This special name, though not a new
phenomena, applies to the Lanthanides and
actinides probably in part due to the fairly
resent discovery of these elements by Seaborg
in the early 1940’s
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PROPERTIES OF THE TRANSITION
ELEMENTS
Oxidation Numbers
• The most common oxidation numbers are +2
and +3 for the free ions.
• The higher states are usually only seen in
combination with oxygen; +7, MnO4-.
Common Oxidation Numbers
We’ll find out latter why this is so
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PROPERTIES OF THE TRANSITION ELEMENTS
Metal Atom Radii
• Atom radii decrease across a period due to Z*
(effective nuclear) increases across a period
because of the effectiveness of electrons in the
same subshell to shield the nucleus’s increasing
number of protons
• The 5th and 6th period metals are almost the same
size due to the lanthanide contraction.
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TRANSITION ELEMENTS
Density
• With similar sizes and increasing masses, the
densities of the 6th period increase dramatically
due to the LC
Melting Point
• The highest melting point occurs in the middle
of each series.
• Higher melting points mean higher attractive
forces.
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Density
Periods
4-6
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PROPERTIES OF THE TRANSITION ELEMENTS
Melting Point
• These higher forces occur with higher numbers
of unpaired electrons.
• The maximum number of unpaired d-electrons
is 5, and the maximum number of f-electrons is
7, with each of these occurring when the orbital
set is half-filled
Melting Points
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TRANSITION ELEMENTS
Magnetism
• One or more unpaired electron give rise to a
property called paramagnetism which is a
strong attraction in a magnetic field.
• A d-orbital set has 0 to 5 unpaired electrons
and an f-orbital set has 0 to 7 unpaired
electrons.
• Atoms or ions with no unpaired electrons
are called diamagnetic.
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PROPERTIES OF THE TRANSITION ELEMENTS
Magnetism
• Ferromagnetism is the ability of the magnetic
domains to be permanently aligned by an
external magnetic field.
• These fields can be eliminated by heating or
strong mechanical vibrations.
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COMMERCIAL PRODUCTION OF TRANSITION
METALS
• The metallic elements are found as ores and are
mixed with impurities called gangue.
• Often, due to size and density, the platinum group
(Ru, Os, Rh, Ir, Pd, and Pt) are found in the earths
crust together and are difficult to seperate
• Once separated, the ore is refined by pyrometallurgy
or hydrometallurgy.
• The first involves heat and the second involves
treatment with aqueous chemicals.
Common Occurrence in Nature
No 5f elements, to unstable
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Iron Production
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• The iron ore is reduced to iron using heat
and coke.
• The coke is primarily carbon and is burned
to produce carbon monoxide. Both these
chemicals are used in the reduction process.
• The silicate impurities are converted to
calcium silicate by the reaction of calcium
oxide and the SiO2.
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Iron Production
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Fe2O3 (s) (hermite) + 3C(s) (coke)  2Fe(l ) + 3CO(g)
Fe2O3 (s) + 3CO(g)  2Fe(l ) + 3CO2 (g)
CO2 (g) + C(s)  2CO(g)
Here CO2 is reduced further in the presence of C(s) to
produce more reducing agent CO(g). Typically limestone,
calcium carbonate is added to initiate this process
Iron Production
• The molten CaSiO3(l) and the impurities that
collect in it are called slag.
SiO2(s) + CaO(s)  CaSiO3(l)
• Phosphorus, sulfur and most of the carbon
are removed from the pig iron using a basic
oxygen furnace (BOF).
• These elements are converted to the
corresponding oxides.
• Special alloys of steel are prepared by adding
other metals like Cr, Ni, and Cu.
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Copper Production
• Both pyrometallurgy or hydrometallurgy are
used to isolate impure copper
• The impure copper can be further refined by
electrolysis, plating pure copper from
solutions of Cu+1. Often iron is involved in
this process (reducing any Cu+2 in solution to
Cu), but since Fe has a higher potential it
will not electroplate out.
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COORDINATION COMPOUNDS
•
•
•
Our current understanding of complex like
NiCl2 explains the electrostatic interaction
between atoms in the complex, primarily
speaking, as we find them in the solid state
However, in the solution phase we find TM
complexes employ a different type of
bonding
Due to TM electron poor nature and their
sheer size with five d-orbitals and low energy
s-orbital, TM employ bonding not typically
seen in main group metals
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Simple Main Group metals
• Sodium cations
bind to water in a
ratio to satisfy the
cation to dipole
charge, often 6
waters attach to a
main group metals
in solution
H H
H
O
H
O
HH
H
O
H
Na+
O
HH
O
O
H
H
Transition Metal Complex
• Instead TM
compounds form
coordination
compounds
• TM bind “Ligands”
to Specific dorbitals so have
very predictable
structures
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COORDINATION COMPOUNDS
•Coordination complexes have ions or molecules
bonded to the metal or metal ion in a region
called the coordination sphere.
•These ions or molecules are called ligands
•These ligands are Lewis bases (available lone
pair for bonding) or have a charge
•Ligands coordinate to empty orbitals on the TM
COORDINATION COMPOUNDS
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• The general formula, NiCl2.6NH3, is actually
[Ni(NH3)6]Cl2, with six ammonia molecules in
the inner coordination sphere and two ionic
Cl in the outer coordination sphere.
• The number of monodentate ligands attached
to the metal is called the coordination
number.
COORDINATION COMPOUNDS
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NiCl2.6NH3, is
actually
[Ni(NH3)6]Cl2
monodentate ligands
Dentate is Latin for
teeth; so
monodentate means
“one bit”
Coordination Number of 6
COORDINATION COMPOUNDS
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• Ligands with two active sights are called
bidentate ligands.
• A single ligand that could coordinate to six
bonding sights on a single metal would be called
a hexadentate ligand
• Ligands that bind more then one site are called
chelating ligands, because of their claw like
structure.
• The general class for these ligands is called
polydentate ligands.
Bidentate Ligands
a.
b.
c.
d.
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Ethylene diamine
Oxalate
Acetyl acetone
Phenanthroline
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Bidentate Ligands
EDTA is a common food preservative
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Bidentate Ligands
COORDINATION COMPOUNDS
Deduce the structures for:
[Fe(en)(NH3)4]Cl3 and [Co(phen)(NO)3Cl]Cl2
• Calculate the oxidation number for the metal
• How many moles of ions per mole of
compound are produced when Ag+ is added?
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[Fe(en)(NH3)4]Cl3
• Fe is +3
• 3 moles of AgCl would form
+3
NH3
H
NH3
N
H2C
Fe
H2C
NH3
N
H
NH3
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[Co(phen)(NO)3Cl]Cl2
• Co+3 and 2 moles of AgCl
+2
O
O
N
Cl
N
Co
O
N
N
O
N
O
O
[Co(phen)(NO)3Cl]+2
Naming Coordination Compounds
1.Standard (Chem 200) Cation, Anion
2.***Complex ion or molecule (Chem 202):
ligand first in alpha order, followed by name of
metal (Ox#), then outer sphere ion.
Ligands:
»anions with ite or ate change the final
“e” to “o” as in nitrate to nitrato.
»anions with ide change to “o” as in
cyanide to cyano.
»molecules uses common name except
for water changes to aqua; ammonia to
ammine; and CO to carbonyl.
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Naming Coordination Compounds
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Ligands: (Cont.)
»multiple simple ligands are prefixed with
di, tri, tetra, penta, or hexa. Complex
ligands are prefixed with bis, tris,
tetrakis, pentakis, or hexakis.
3.If the complex is an anion, the suffix “ate” is added
to the metal name [Fe(CO)2-] = dicarbonylironate(0).
4.The name of the metal is followed by the oxidation
number of the metal in Roman numerals.
PRACTICE THESE RULES !!!!!!!
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Naming Coordination Compounds
Name
K2[Ni(CN)4]
Na[Cr(C2O4)2(H2O)2]
Tetracyanonickle(II) potassium
Diaquabis(oxylato)chromium(III) sodium
[Ru(phen)4]Cl3
Tetrakis(phenanthroline)ruthunium(III) chloride
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Formula
aquachlorobis(ethylenediamine)
cobalt(III) chloride
[Co(H2O)(Cl)(en)2]Cl2
Pentacarbonyliron(0)
Fe(CO2)5
Triaminechloroetheylenediamenecobalt(III)
[Co(NH3)3(Cl)(en)]2+
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STRUCTURES OF COORDINATION COMPOUNDS
AND ISOMERS
Common Geometries
• Linear, ML2
• Tetrahedral ( not d8), ML4
• Square planar (d8), ML4
• Octahedral, ML6.
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Isomerism
• Structural isomers have different
arrangements of the atoms.
• Geometric isomers have the same atom
attachments but different geometrical
arrangements.
• Stereoisomers that have a special difference
based on chirality are called optical isomers,
which have mirror image forms that cannot
be superimposed.
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Structural Isomerism of C4H10
H2
C
CH3
C
H2
H3C
CH3
CH
H3C
CH3
Geometric Isomerism
• Tetrahedral, none
• Square planar and octahedral, cis
and trans
• Octahedral, fac and mer.
• See various Figures.
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Geometric Isomerism
Cis
Trans
Square Planar
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Geometric Isomerism
Cis
Trans
Pt(en)2Cl2
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Geometric Isomerism
Fac= facial
Mer = meridianal
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Linkage Isomerism
Optical Isomerism
• If two mirror image isomers are
nonsuperimposable they have chirality and
they are known as enantiomers.
• Optical isomers frequently rotate planepolarized light.
• One isomer rotates left, levero (l), and the
other rotates right, dextero (d).
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Optical Isomerism
– The molecule is rotated to put the lowest priority group
back
» If the groups descend in priority (a,b then c) in clockwise
direction the enantiomer is R
» If the groups descend in priority in counterclockwise
direction the enantiomer is S
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–The Polarimeter
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Optical Isomerism
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nonsuperimposable
nonsuperimposable
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BONDING IN COORDINATION COMPOUNDS
• There are two major theories to explain the
bonding in coordination compounds:
–Molecular orbital theory (valence
bond).
–Crystal field theory.
• The first is a covalent bonding theory and the
second is an electrostatic bonding theory.
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CRYSTAL FIELD THEORY
• In the crystal field theory, the ligand is
responsible for altering or splitting the d
orbital energy levels of the metal ion.
d-orbitals in a Ligand “Free”
complex
d-orbitals where a
metal has Ligands
attached
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CRYSTAL FIELD THEORY
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CRYSTAL FIELD THEORY
Splitting seen in all octahedral complexes
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CRYSTAL FIELD THEORY
• The tetrahedral and square planar,
different splitting of the d energy
levels.
• Tetrahedral: dxy, dxz and dyz orbitals
point toward ligands
• Square planar: dx2-y2 point right at
ligands, dxy and dz2 do as well.
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CRYSTAL FIELD THEORY
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CRYSTAL FIELD THEORY
Cr2+ [Ar] 3d44s0, an octahedral complex
Spin pair energy determines which (Hund’s)
CRYSTAL FIELD THEORY
• The ligand fields may be strong or weak.
• Strong field ligands cause a large splitting
resulting in low-spin complexes
• Weak field ligands cause only a small energy
difference between the d orbital energy levels
and results in high-spin complexes
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CRYSTAL FIELD THEORY
Magnetically it is easy to tell that the cyano complex
is low spin
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CRYSTAL
FIELD
THEORY
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CRYSTAL FIELD THEORY
Octahedral
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• High spin has Do< P and low spin has Do> P,
where P is the pairing energy.
• Do is always Do> P for metal atoms using
4d and 5d electrons.
• For 3d metals the relationship between Do and P
is determined by the nature of the ligand.
Tetrahedral
• The tetrahedral splitting is the
opposite of the octahedral splitting.
•All tetrahedral complexes have
Dt< P and are thus high spin.
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Square Planar
• The square planar splitting is different from
the others is several ways.
• There are 3 D's with the largest being Dsp.
• Square planar only exists for d8 and
coordination numbers of four.
• These complexes are always low spin
since Dsp > P for all square planar
complexes.
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THE COLORS OF COORDINATION
COMPOUNDS
• The colors of complexes give us an indication
of the splitting energies involved.
• This often allows us to correctly predict the
high and low spin cases for octahedral
complexes.
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COLORS
• Color addition and subtraction is an important
concept in understanding ligand field strength.
• An absorption spectrum tells us what wavelength
is absorbed.
• The complimentary color is the observed color and
represents white light minus the absorbed light.
• Visible light has wavelength from 700 nm for red
to 400 nm for violet.
• Color discs can be helpful in understanding
perceived colors.
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It absorbs green and
blue
If solution is red
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COLORS
• The following spectrum for the
hexamminecobalt(III) complex.
• The absorbed color is blue(indigo) which
results in a yellow complex ion.
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[Co(NH3)6]3+
Complex is yellow, absorbs blue
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COLORS
[Co(NH3)6]3+
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CRYSTAL FIELD THEORY
Spectrochemical Series
Halides < C2 O4 -2 < H 2 O < NH3 = en < phen < CNweak field
low D
  donor
strong field
high D
  acceptor
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The Spectrochemical Series of Ligands
• The higher the energy absorbed by the
complex ion, the larger the splitting energy,
and the stronger the ligand field.
• Field strength decreases with increasing
numbers of these interactions and with
increasing size: I-, Br-, Cl-, F-, OH-, H2O.
• Those ligands with neither type interactions
are intermediate in strength: NH3, en, phen.
The Spectrochemical Series of Ligands
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• Weak field ligands have L -L-->M
>M(p) interactions due to lone
pairs on the ligand.
• Strong field ligands have M -Ligands donates electrons through electron occupied
> L()* interaction due to
 overlap example would be F's 2p orbital
empty * molecular orbitals:
CN-, CO.
L<--M
O
C
Lignads with empty  orbitals take electrons
from the metal to form a bond