Title: Transition Metals
1Transition Metals
- Be familiar with the electron configurations,
properties and common oxidation states of
transition metals (Table 21.2), and know that
aqueous solutions of their ions are highly
colored (photos on p 989, 993, 997, 1002, 1015) - Know that transition metals form complex ions,
i.e. cations that are surrounded by neutral
molecules with nonbonding electron pairs (called
ligands, denoted L) (p988) know that
coordination number is number of ligands
surrounding the cation (Fig 21.5, Table 21.12)
know the most common ligands (Table 21.14) - Remember what the d orbitals look like (Fig
21.20). Appreciate that the crystal field model
accounts for the colors of transition metal ions
the d orbital energies are split into two sets
separated by an energy ? (Fig 21.21) the
occupation of the orbitals by electrons (and the
paramagnetism of a complex) depends on how big ?
is (strong field or weak field, Fig 21.22) the
ligands determine the strength of the field
(learn about the spectrochemical serioes on p
1013) the color of a complex ion solution also
depends upon D (Fig 21.23, Table 21.16, Table
21.17). - Monday focus reading on sections 21.1, 21.3 and
21.6. Wednesday organic chemistry, sections
22.1-22.4. Don't worry about naming or
reactions. Friday Natural and Artificial
Polymers, sections 22.5 22.6. Chapter 22 - Homework problems from Ch 21 19, 21, 43, 45,
47, 51. Ch 22 23, 39, 51, 71, 75, 83, 85, 99.
2Transition Metals
3Electron Configurations, Properties and Common
Oxidation States of Transition Metals
4Transition Metal Ion Salts Are Often Highly
Colored
5Transition Metal Cations Form Complex Ions (also
called coordination complexes)
- Complex Ion transition metal cation surrounded
by LIGANDS - Ligand molecule or ions that have nonbonding
electron pairs - Bonding is called coordination
6Coordination Number
- Coordination number the number of ligands
surrounding a central cation in a transition
metal complex. - Common coordination numbers are 2, 4 and 6
- The geometries of the ligands about the central
atom are as shown
7Common Ligands
- Ligands have nonbonding electron pairs to donate
to the transition metal cation - Dentate number of electron pairs that
coordinate to the central metal cation - Unidentate, bidentate
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9Heme
10Metalloprotein Complex Hemoglobin
11Remember the d Orbitals?
12Transition Metals Use Their Valence d Orbitals
and Orbital Hybridization for Coordination
- d2sp3 hybrids on Co2 interact with ammonia
ligands in this complex ion
13The Ligands Create a Ligand Field
- The symmetry of the electric field around an
isolated metal cation is spherical the same no
matter what direction you are looking - When you arrange ligands around the central metal
cation, the symmetry of the electric field about
it has the geometry determined by the arrangement
of the ligands (e.g. Octahedral, tetrahedral,
linear, etc.)
14Three of the d orbitals have a different spatial
relationship with crystal field than the other two
15Two Classes of d Orbitals in an octahedral ligand
field
- The lobes of two d orbitals point ALONG the axes
of the octahedron - The lobes of three d orbitals point BETWEEN the
axes of the octahedron - The environment of the orbitals along the axes is
different from that of those that point between
the axes - Because the orbitals are in different
environments, they have different energies - The five d orbitals are split into two groups a
group of two denoted eg and a group of three
denoted t2g
16Crystal Field Splitting
17Where are the metal ion electrons, then?
- Depends upon how big D is!
- Consider case of d6 metal ion metal ion with 6
d electrons (e.g. Co2) - Big D electrons don't have enough energy to
occupy the eg orbitals - Note that the paramagnetism (number of unpaired
electrons) is different in the two cases. - High spin, low spin
18Why Are Some Transition Metal Ions Colored?
19Why are Some Transition Metal Ions
Colored?...because they absorb light in the
visible region of the electromagnetic spectrum
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21Why Do Some Transition Metal Ions Absorb Light in
the Visible Region of the Electromagnetic
Spectrum?
- ...because they have electrons that are able to
undergo transitions between the eg and t2g
orbitals, and - ...because D is in the visible region of the
electromagnetic spectrum
22What Determines if Electrons Can Undergo
Transitions Within the d Shell?
- Consider the case of the silver ion, Ag
- Ag is d10 has 10 electrons in its d orbitals.
- Regardless of the value of D, the electrons can't
undergo transitions because the d orbitals are
fully occupied. There's nowhere to go!
23What Determines How Big D Is?
- Ligands are one very important influence!
- Ligands that interact much more strongly with the
metal cation will increase the splitting between
the d orbitals. - Spectrochemical series (p 1013) determined by
experiment - Strong, big D Weak, small D
- CN- gt NO2- gt NH3 gt H2O gt OH- gt F- gt Cl- gt Br- gt I-
24Different Ligands Make the Same Cation Different
Colors