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Transition Metals
Occupy the d-block of periodic tableHave d-electrons in valence shell
Some characteristics of Transition Metals and theircompounds
1. Exhibit more than one oxidation state2. Many of their compounds are colored3. They exhibit interesting magnetic properties.4. They form an extensive series of compounds
known as metal complexes or coordinationcompounds.
e.g., Reduction of V5+ by metallic Zn
VO2(H2O)4+ yellow-orange
VO(H2O)52+ blue
V(H2O)63+ green
V(H2O)62+ violet
Exhibit more than one oxidation state
Many of their compounds are colored
Transition Metals
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ELECTRON CONFIGURATIONS3d elements: Sc → Zn
Ar 3s23p6 Sc [Ar]3d14s2
K [Ar]4s1 Ti [Ar]3d24s2
Ca [Ar]4s2 . . . . . .Zn [Ar]3d104s2
Note: 4s is filled before 3d, but when oxidized, 4s electrons are lostbefore 3d.
Ti [Ar]3d24s2
Ti2+ [Ar]3d24s0
Ti3+ [Ar]3d14s0
Ti4+ [Ar]3d04s0
Ti5+ does not exist!
TRANSITION METALS: Sc→Mn
Oxidation States:Highest oxidation states of Sc, Ti, V, Cr, Mn = number ofvalence (4s + 3d) electrons.
Sc [Ar]3d14s2 Sc3+ [Ar] maximumMn [Ar]3d54s2 Mn7+[Ar] maximum
Trend from Sc → Mn:The max. oxidation state becomes increasingly unstable.Sc3+, Ti4+ are stable (maximum oxidation states).Sc2O3 Stable oxide.Mn7+ Exists but is easily reduced.MnO4
- Strong oxidizing agent.
Transition Metals
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Magnetic Properties
Diamagnetic:unaffected by a magnetic fieldno unpaired electrons
Paramagnetic:influenced by a magnetic fieldunpaired electrons
Transition metals and their compounds are oftenparamagnetic⇒Have unpaired d-electrons
Eg. Ti2+
Mn2+
TRANSITION METAL IONSTransition metal ions are Lewis acids ⇒ they acceptelectron pairs.
Ligands are Lewis bases ⇒ molecules or ions whichdonate electron pairs.
Ligands bonded to metal ions ⇒ metal complexes orcoordination compounds.
Coordination number:number of electron donor atoms attached to the metal.
Chelates are ligands possessing two or more donoratoms.
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COORDINATION COMPOUNDS• Metals-Lewis acids• Ligands -Lewis bases.
Ligand molecules have lone pair electrons.– Anions -
F−, Cl−, Br−, CN−, SCN−, NO2−, etc.
– Neutral ligands: NH3, H2O, CO• mono-dentate -(single claw to hold onto metal d orbital)
Ex. :NH3, H-:O:-H , CH3-:O:-H• Bi-dentate -(has 2 claws to hold onto metal d orbitals). Has 2
or more functional groups on ligands that have lone pairsExample :NH2-CH2-CH2-H2N:(= en or ethylenediammine)
Coordination # = 4
Tetrahedral, e.g. [Zn(NH3)4]2+
Square Planar, e.g. [Ni(CN)4]2−
Square Planar,e.g. [PtCl3(C2H4)]−
Pt
Cl
Cl
Cl
C
H H
C
H H
COORDINATION COMPOUNDS
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Coordination # = 6
Octahedral, e.g. [CoF6]3-
Octahedral, e.g. [Co(en)3]3+
Co
F
F F
F F
F
Co
N
N N
N N
N
COORDINATION COMPOUNDS
IMPORTANT CHELATING LIGANDS
NCH2CH
2N
: :
CH2COH
CH2COH
O
O
HOCCH2
HOCCH2
O
O
Porphine
EDTA
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CHELATE EFFECTChelating ligands form more stable compounds.
[Ni(H2O)6]2+ + 6NH3 ↔ [Ni(NH3)6]2+ + 6H2O Kf = 4x108
[Ni(H2O)6]2+ + 3en ↔ [Ni(en)3]2+ + 6H2O Kf = 2x1018
CHELATE EFFECT IS AN ENTROPY EFFECT
Cd2+ + 4CH3NH2 ↔ [Cd(CH3NH2)4]2+
ΔG° = −37.2kJ ΔH° = −57.3kJ ΔS° = −67.3J/K
Cd2+ + 2en ↔ [Cd(en)2]2+
ΔG° = −60.7kJ ΔH° = −56.5kJ ΔS° = +14.1J/K
PROPERTIES OF TRANSITION METALS
Transition Metal Complexes have different properties –• color (all except Zn or Sc3+ white compounds)• solubility-depends on complex reduction potential
– lower than free ions
Ag+(aq) + e− → Ag(s) E°1/2= +0.80V
[Ag(CN)2]−(aq) + e− →Ag(s)+ 2CN−(aq) E°1/2 = −0.31V
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Co
F
F F
F F
F
Co3+ Co3+
F- F-
F-
F-F-
F-
(3d6)
CRYSTAL FIELD SPLITTING
dx2-y2 dz2
dxy dyz dxz
Δ
Δ = crystal field splitting energySpectrochemical series: CN− > NO2
− > en > NH3 > H2O > OH- > F− > Cl−
decreasing Δ
d-electronenergy
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SPECTROCHEMICAL SERIES
CN-
CONO2
-
enNH3H2OOxalateOH-
F-
SCN-
Cl-
Br-
I- Color seen is complementary toabsorbed colorAbsorbed light
Strong fieldligands
Weak field ligands
UV
IR
COLOR WHEEL
RED
GREEN
VIOLETORANGE
YELLOWBLUE
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CRYSTAL FIELD SPLITTING ENERGY
Δ depends on1. Metal2. Oxidation state3. Ligands
P = spin pairing energyP does not depend on the ligands
P < Δ ⇒ Low Spin ComplexP > Δ ⇒ High Spin Complex
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SPIN PAIRINGOCTAHEDRAL COMPLEXES
E
CoF63-
Co(CN)63-High spin
Paramagnetic Low spin (spin paired)diamagnetic
USES OF TRANSITION METALSTiLighter and stronger than steel.Ti and its alloys are used in jet engines, planes, and in special hightemp applications, e.g. in the reentry shield on the Apollo capsules.TiO2 is a white pigment in all white paints.
VVanadium steel (Fe/V alloy) is the toughest steel known. It is usedin car springs.V2O5 is a catalyst used in sulfuric acid production.
CrStainless Steel = 73% Fe,18% Cr, 8% Ni, 1% CChromium is electroplated to make shiny metal parts.
MnMn steel (Fe/Mn alloy) is very tough and can withstand shock andabrasion – used in bulldozer blades and armor plates on warships.
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CHROMIUM OXIDES
Cr(III) Oxide, Cr2O3Abrasive, RefractorySemiconductor, Green pigmentAmphoteric
Cr(IV) Oxide, CrO2Recording tape (magnetic material)
Cr(VI) Oxide, CrO3RedChrome plating, corrosion inhibitor
Na2Cr2O7Tanning, metal corrosion inhibitor