Transition Metals Occupy the d-block of periodic table Have d-electrons in valence shell Some...
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Transcript of Transition Metals Occupy the d-block of periodic table Have d-electrons in valence shell Some...
Transition Metals
Occupy the d-block of periodic tableHave d-electrons in valence shell
Some characteristics of Transition Metals and their compounds
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 coordination compounds.
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
ELECTRON CONFIGURATIONS
3d 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 lost before 3d.
Ti [Ar]3d24s2
Ti2+ [Ar]3d24s0
Ti3+ [Ar]3d14s0
Ti4+ [Ar]3d04s0
Ti5+ does not exist!
TRANSITION METALS: ScMn
Oxidation States:Highest oxidation states of Sc, Ti, V, Cr, Mn = number of valence (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
Magnetic Properties
Diamagnetic:unaffected by a magnetic fieldno unpaired electrons
Paramagnetic: influenced by a magnetic fieldunpaired electrons
Transition metals and their compounds are often paramagneticHave 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 # = 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
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
N C H
2
C H
2
N
: :
C H2
C O H
C H2
C O H
O
O
H O C C H2
H O C C H
2
O
O
Porphine
EDTA
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+
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
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
= crystal field splitting energy Spectrochemical series: CN > NO2
> en > NH3 > H2O > OH- > F > Cl
decreasing
d-electronenergy
SPECTROCHEMICAL SERIES
CN-
CONO2
-
enNH3
H2OOxalateOH-
F-
SCN-
Cl-
Br-
I- Color seen is complementary to absorbed color
Absorbed light
Strong fieldligands
Weak field ligands
UV
IR
COLOR WHEEL
RED
GREEN
VIOLETORANGE
YELLOWBLUE
CRYSTAL FIELD SPLITTING ENERGY
depends on1. Metal2. Oxidation state3. Ligands
P = spin pairing energyP does not depend on the ligands
P < Low Spin ComplexP > High Spin Complex
SPIN PAIRINGOCTAHEDRAL COMPLEXES
E
CoF63-
Co(CN)63-High spin
Paramagnetic Low spin (spin paired)diamagnetic
USES OF TRANSITION METALS
TiLighter 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.
VVanadium steel (Fe/V alloy) is the toughest steel known. It is used in 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 and abrasion – used in bulldozer blades and armor plates on warships.
CHROMIUM OXIDES
Cr(III) Oxide, Cr2O3
Abrasive, RefractorySemiconductor, Green pigmentAmphoteric
Cr(IV) Oxide, CrO2
Recording tape (magnetic material)
Cr(VI) Oxide, CrO3
RedChrome plating, corrosion inhibitor
Na2Cr2O7
Tanning, metal corrosion inhibitor