transition metals ii

8/21/2019 Transition Metals II

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CHEM0902/C06K

INORGANIC CHEMISTRY

First row transition metals

Catalysts and coloured compounds(continued)

Ainka Brown

[email protected] 1



Transition metals

2

Electronicconfiguration

Catalytic ability Colouredcompoundsand complexes



Orbital shapes and energies

3

1

2 3 4

nucleus




• Filling electrons:

- minimise energy

- minimise repulsion

- when a shell is filled with electrons it raises

energy of shell above (HOW???)

4

What is meant by a low energy shell?

Assumption:

Sub-orbitals have same energy in all elements.

Generally true, but not always




5



Period 4: unexpected electron configurations

6

K [Ar] 3d0 4s1

Ca [Ar] 3d0 4s2

Sc [Ar] 3d1 4s2

Ti [Ar] 3d2 4s2

V [Ar] 3d3 4s2

Cr [Ar] 3d5 4s1

Mn [Ar] 3d5 4s2

Fe [Ar] 3d6 4s2

Co [Ar] 3d7 4s2

Ni [Ar] 3d8 4s2

Cu [Ar] 3d10 4s1

Zn [Ar] 3d10

4s2

*

*

4s orbitals have a

slightly lower energy

than 3d orbitals)

1s

2s

2p

3s3p4s3d

4p



Unexpected electron configurations

Predicted

Actual

2 out of 3 e-

are in lower Esub-orbital

Lower E outweighs

electronic replusion

All the e- are in higher E

sub-orbital

7

RE




Similar trend for Ti and V

Predicted Actual

8

ER




Predicted Actual

1 of the e- is in lower E sub-

orbital plus no repulsion

All e- are in higher E sub-orbital,

plus repulsion

OR

Four of the e- are in higher E sub-

orbital, plus repulsion

9

ER




Predicted Actual

2 of the e- are in lower E sub-

orbital plus less repulsion

All e- are in higher E sub-orbital,

plus repulsion

10

Similar trend for Fe and Co

ER




11

Predicted Actual

OR

All e- are in higher E sub-orbital,plus repulsion

2 of the e- is in lower E sub-orbital plus less repulsion

Lower energy arrangement

In both there is repulsion

and a half-filled orbital



Remembering configurations

• (Exceptions Cr and Cu)

12

4s

3d

Think “2 10”

What is configuration of Co3+ ?



Characteristics of transition metals

• Criteria:

variable oxidation state

ions with partially-filled d-orbitals

catalytic activity

formation of complex ions

coloured complexes/compounds

13



Oxidation states of transition metals

• Lose 4s electrons first (shielding by 3d)

• Can lose/share both 3d and 4s

• Readiness to be oxidised decreases left to right

(correlation with I.E and Zeff )

•

Oxidation potentials show will readily form +2 and +3cations in H+

(Except Cu. Needs something stronger)

14



Oxidation potentials

Eθ /V Oxidation ½ eqn. Eθ /V Oxidation ½ eqn. 0.45 Fe(s) → Fe2+ + 2é 2.08 Sc(s) Sc3+ + 3é 0.28 Co(s) → Co2+ + 2é 1.63 Ti(s) Ti2+ + 2é 0.26 Ni(s) → Ni2+ + 2é 1.18 V(s) V2+ + 2é

-0.34 Cu(s) → Cu2+

+ 2é 0.91 Cr(s) Cr2+

+ 2é 0.76 Zn(s) → Zn2+ + 2é 1.18 Mn(s) Mn2+ + 2é

H2(g) → H+ + 2é Eθ = 0.00 V 15



Oxidation states of transition metals

• High oxidation state = good oxidizing agents,

(e.g. Cr2O72-

, MnO4-)

• Low oxidation state in early part of series = goodreducing agent

(e.g. V2+, Cr2+)

• Later in series poor reducing agent (high Zeff )

• (e.g.Co2+, Ni2+, Cu2+ and Zn2+)

16



Catalytic activity

• A catalyst is a substance which speeds up a reaction, butis chemically unchanged at the end of the reaction

• Characteristics:

ability to change oxidation state.

ability to adsorb substances unto their surface(helps to activate them)

• Two types:

heterogenous

homogenous

17

HOW ?



Heterogenous vs. homogenous

18

Heterogenous Homogenous



Some heterogenous catalysts

Catalysts Reaction MnO2 Decomposition of H2O2 V2O5 Contact Process

Fe Haber Process Pt/Rh Ostwald Process

Ni/Pd/Pt Hydrogenation

19



Heterogenous catalysts

20



Heterogenous catalysts

Reading Assignment!!!!!!

How does V2

O5

catalyse the Contact Process?

21



Homogenous Catalysis

22

Peroxodisulfate + Iodide

What are the

changes in oxidation

state?



Formation of complex ions

• Trasition Metal ions can undergo dative covalentbonding

(Empty 3d, 4s, 4p and 4d orbitals can accommodate)

• Examples in nature

(hemoglobin, vitamin B12)

• Do not need to know how bonding

occurs in depth

23



Bonding in Complex ions

• Ligands – molecule or ions surrounding metal ion

(have lone pair or negative charge)

e.g. H2O, Cl-, NH3 etc.

• Donor atom – atom that does the actual bonding

• Coordination number – number of donor atoms aroundthe metal ion

24



Bonding in Complex ions

25Taken from: www.chemguide.co.uk

Note charge on

metal is not

quenched!!!

Just re-distributed!!



Coloured ions/compounds

• In complexes d-orbitals have different energies

• Ligands cause electron-electron repulsions

• d-orbital splitting occurs

26

∆ E ∆ E

Which +2

transition metal

cation does this

represent ?OR




• Can have d→ d transitions

• (absorb visible light)

• Colour is dependent on ∆ E

27

∆ E

600 nm

560 nm

490 nm430

400 nm

800 nm

650 nm




• ∆ E is affected by:

- oxidation state of ion

- ligands

28

CuSO4 Co(NO3)2

K2Cr2O7

K2CrO4

NiCl2

KMnO4

∆ E

There are

anomalies.

Colour not

due to

d→d



Coordination Chemistry

The colours of Chemistry and the

Chemistry of colours

Ainka Brown

[email protected] 29



Transition metal complexes

• Also known as coordination compounds

• Used as catalysts, medicines and pigments

• Objectives

applying the IUPAC rules for naming

determining and drawing isomers

geometric (cis, trans)

optical

30



Transition metal complexes

• May be neutral compounds, cations or anions

(Depends on the ligand)

• Terms to know:

- ligand

- donor atom

- coordination number

- chelate

31



Ligand Name Name Molecule Ammine Ammonia :NH3

Aqua Water H2O: Carbonyl Carbon monoxide :CO Nitrosyl Nitrogen oxide :NO

Phosphine Phosphine :PH3 ethylenediamine ethylenediamine en

Neutral ligands

What is the

structure of en? 32



Anionic ligands

33

Ligand Name Name Ion Chloro Chloride Cl- bromo bromide Br- Fluoro Fluoride F- Cyano Cyanide -CN

Hydroxo Hydroxide -OH Nitro Nitrite NO2

- Carbonato Carbonate CO3-

Oxalato Oxalate C2O42-

Oxo Oxide O2-

What is the structure of oxalate?



Nomenclature

• Please read the relevant section in McMurray

and Fay!!!!!

• We will discuss briefly

•

Practice, practice and practice some more

34



Nomenclature

•For salts name cation before the anion, with a spacebetween the names.

• Ligands are named in alphabetical order (prefixes

ignored)

Use di-, tri-, tetra-, etc if more than one monodentate

ligand.

For chelates use bis-, tris- etc. if more than one

35

6 ammonias? 2 waters and 4 chlorides ?

2 oxalates and 2 waters? 2 oxalates and 2 chlorides?



Nomenclature

• No space between ligand names, no space betweenlast ligand and metal

•

Roman numerals in brackets to show oxidation stateof metal

• If metal is part of anionic complex it has a “metallate

name”

36



“Metallate names”

Metal Anion name

Titanium titanate

Vanadium vanadate

Chromium chromateManganese manganate

Iron ferrate

Cobalt cobaltate

Nickel nickelate

Copper cuprate

Zinc zincate

37



Nomenclature

[Co(NH3)6]Cl3

[Fe(C2O4)3]3-

[Cu(NH3)4]SO4

Na[Cr(OH)4]

Hexaamminecobalt(III) chloride

Trisoxalatoferrate(III) ion

Tetraamminecopper(II) sulfate

Sodium tetrahydroxochromate(III)

38

transition metals ii

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