Transcript TRANSITION METALS - Pennsylvania State University

Transition Metals
Occupy the d-block of periodic table
Have d-electrons in valence shell
Some characteristics of Transition Metals and their
compounds
1.
2.
3.
4.
Exhibit more than one oxidation state
Many of their compounds are colored
They exhibit interesting magnetic properties.
They form an extensive series of compounds
known as metal complexes or coordination
compounds.
Transition Metals
Exhibit more than one oxidation state
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
Many of their compounds are colored
ELECTRON CONFIGURATIONS
3d elements: Sc  Zn
Ar 3s23p6
K [Ar]4s1
Ca [Ar]4s2
Sc [Ar]3d14s2
Ti [Ar]3d24s2
.
.
.
.
.
.
Zn [Ar]3d104s2
Note: 4s is filled before 3d, but when oxidized, 4s electrons are lost
before 3d.
Ti
Ti2+
Ti3+
Ti4+
Ti5+
[Ar]3d24s2
[Ar]3d24s0
[Ar]3d14s0
[Ar]3d04s0
does not exist!
Transition Metals
TRANSITION METALS: ScMn
Oxidation States:
Highest oxidation states of Sc, Ti, V, Cr, Mn = number of
valence (4s + 3d) electrons.
Sc [Ar]3d14s2
Mn [Ar]3d54s2
Sc3+ [Ar]
Mn7+[Ar]
maximum
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.
MnO4Strong oxidizing agent.
Magnetic Properties
Diamagnetic:
unaffected by a magnetic field
no unpaired electrons
Paramagnetic:
influenced by a magnetic field
unpaired electrons
Transition metals and their compounds are often
paramagnetic
Have unpaired d-electrons
Eg.
Ti2+
Mn2+
TRANSITION METAL IONS
Transition metal ions are Lewis acids  they accept
electron pairs.
Ligands are Lewis bases  molecules or ions which
donate electron pairs.
Ligands bonded to metal ions  metal complexes or
coordination compounds.
Coordination number:
number of electron donor atoms attached to the metal.
Chelates are ligands possessing two or more donor
atoms.
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 pairs
Example :NH2-CH2-CH2-H2N:
(= en or ethylenediammine)
COORDINATION COMPOUNDS
Coordination # = 4
Tetrahedral, e.g. [Zn(NH3)4]2+
Square Planar, e.g. [Ni(CN)4]2
Cl
Square Planar,
e.g. [PtCl3(C2H4)]
H
H
C
Cl
Pt
C
Cl H
H
COORDINATION COMPOUNDS
Coordination # = 6
F
Octahedral, e.g. [CoF6]3-
F
F
Co
F
F
F
Octahedral, e.g. [Co(en)3]3+
N
N
N
Co
N
N
N
IMPORTANT CHELATING LIGANDS
Porphine
O
HOCCH2
HOCCH2
O
:
NCH2CH2N
:
EDTA
O
CH2COH
CH2COH
O
CHELATE EFFECT
Chelating 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+
G° = 37.2kJ
H° = 57.3kJ S° = 67.3J/K
Cd2+ + 2en  [Cd(en)2]2+
G° = 60.7kJ
H° = 56.5kJ
S° = +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
FCo3+
(3d6)
Co3+
FF-
F
F-
Co
FF-
F
F
F
F
F
CRYSTAL FIELD SPLITTING
d-electron
energy
dz2
dx2-y2

dxy
dyz
dxz
 = crystal field splitting energy
Spectrochemical series:
CN > NO2 > en > NH3 > H2O > OH- > F > Cl
decreasing 
SPECTROCHEMICAL SERIES
UV
IR
Absorbed light
CNCO
Strong field
NO2ligands
en
NH3
H2O
Oxalate
OHFWeak field
SCN
ligands
ClBrIColor seen is complementary to
absorbed color
COLOR WHEEL
RED
VIOLET
ORANGE
BLUE
YELLOW
GREEN
CRYSTAL FIELD SPLITTING ENERGY
 depends on
1. Metal
2. Oxidation state
3. Ligands
P = spin pairing energy
P does not depend on the ligands
P <   Low Spin Complex
P >   High Spin Complex
SPIN PAIRING
OCTAHEDRAL COMPLEXES
E
CoF63High spin
Paramagnetic
Co(CN)63Low spin (spin paired)
diamagnetic
USES OF TRANSITION METALS
Ti
Lighter and stronger than steel.
Ti and its alloys are used in jet engines, planes, and in special high
temp applications, e.g. in the reentry shield on the Apollo capsules.
TiO2 is a white pigment in all white paints.
V
Vanadium steel (Fe/V alloy) is the toughest steel known. It is used
in car springs.
V2O5 is a catalyst used in sulfuric acid production.
Cr
Stainless Steel = 73% Fe,18% Cr, 8% Ni, 1% C
Chromium is electroplated to make shiny metal parts.
Mn
Mn steel (Fe/Mn alloy) is very tough and can withstand shock and
abrasion – used in bulldozer blades and armor plates on warships.
CHROMIUM OXIDES
Cr(III) Oxide, Cr2O3
Abrasive, Refractory
Semiconductor, Green pigment
Amphoteric
Cr(IV) Oxide, CrO2
Recording tape (magnetic material)
Cr(VI) Oxide, CrO3
Red
Chrome plating, corrosion inhibitor
Na2Cr2O7
Tanning, metal corrosion inhibitor