Staff Site Universitas Negeri Yogyakarta

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Transition Metals

Similarities within a given period

and within a given group.

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20_431

Uno Une Uun Uuu

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20_432 d-block transition elements

*Lanthanides

†_Actinides

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0.2

Atom

ic ra

dii (n

m)

Atomic number

La 1st series (3d) 2nd series (4d)

3rd series (5d)

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Metallic Behavior/Reducing Strength

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Color and Magnetism

e- in partially filled d sublevel absorbs visible light moves to slightly higher energy d orbital

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Chromium

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Valence-State Electronegativity

Electronegativity, EN:

electron “pulling power”

Valence-state EN:

metal in higher oxidation state is more positive

has stronger pull on electrons is more electronegative

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Coordination Compound

Consist of a complex ion and necessary counter ions

[Co(NH₃)₅Cl]Cl₂

Complex ion: [Co(NH₃)₅Cl]2+

Co3+ + 5 NH₃ + Cl = 1(3+) + 5 (0) + 1(1-) = 2+

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-Complex ion remains intact upon dissolution in water

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Complex Ion

Species where transition metal ion is surrounded by a certain number of ligands.

Transition metal ion: Lewis acid

Ligands: Lewis bases

Co(NH₃)₆3+

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Ligands

Molecule or ion having a lone electron pair that can be used to form a bond to a metal ion

(Lewis base).

coordinate covalent bond: metal-ligand bond

monodentate: one bond to metal ion

bidentate: two bond to metal ion

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Formulas of Coordination Compounds

1. Cation then anion

2. Total charges must balance to zero

3. Complex ion in brackets

K₂[Co(NH₃)₂Cl₄]

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Names of Coordination Compounds

1. Cation then anion

2. Ligands

in alphabetical order before metal ion neutral: molecule name* anionic: -ide  -o

prefix indicates number of each

3. Oxidation state of metal ion in () only if more than one possible

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Examples

K₂[Co(NH₃)₂Cl₄]

potassium diamminetetrachlorocobaltate(II)

[Co(NH₃)₄Cl₂]Cl

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20_441

Isomers

(same formula but different properties)

Stereoisomers

(same bonds, different spatial arrangements) Structural

isomers

(different bonds)

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Structural Isomerism 1

Coordination isomerism:

Composition of the complex ion varies.

[Cr(NH₃)₅SO₄]Br

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Structural Isomerism 2

Ligand isomerism:

Same complex ion structure but point of

attachment of at least one of the ligands differs.

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Linkage Isomers

[Co(NH₃)₅(NO₂)]Cl₂

Pentaamminenitrocobalt(III) chloride

[Co(NH₃)₅(ONO)]Cl₂

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Stereoisomerism 1

Geometric isomerism (cis-trans):

Atoms or groups arranged differently spatially relative to metal ion

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Stereoisomerism 2

Optical isomerism:

Have opposite effects on plane-polarized light (no superimposable mirror images)

Unpolarized

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20_448

Left hand

Right hand

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20_449

Mirror image of Isomer I

Isomer I Isomer II

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Cl

Isomer II Isomer I

cis trans

Isomer II cannot be superimposed exactly on isomer I. They are not identical structures. The trans isomer and

its mirror image are identical. They are not isomers of each other.

Isomer II has the same structure as the mirror image of isomer I. (b)

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Crystal Field Theory

Focus: energies of the d orbitals

Assumptions

1. Ligands: negative point charges

2. Metal-ligand bonding: entirely ionic

strong-field (low-spin): large splitting of d orbitals

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20_454



e_g(d_z2, dx2 – y2)

t_2g(d_xz, d_yz, d_xy)

Free metal ion 3d orbital

energies E

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[V(H₂O)₆]2+ [V(H₂O)₆]3+

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– –

–

– –

– –_–– –

d_z2 d_x2 – y2

d_xy d_xz d_yz

(a) (b)

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E

Free metal ion Complex d_z2 Free metal ion Complex

d_x2_{- y}2

Square Planar & Linear Complexes

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