2. Transition Metals

8/13/2019 2. Transition Metals

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TRANSITION ELEMENTS


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Write valence electron configurations for transition-metal atoms andions.

Identif the li ands and their donor atoms. Determine coordinationnumber and oxidation state of the metal, and the charge on anycomplex ion.

Write formulas of coordination com lexes and Name coordination

compounds. Identify types of isomers, and draw structures of isomers

show the number of unpaired electrons and the hybrid orbitals used bythe metal ion.

show the number of unpaired electrons.


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e use many o trans t on e ements n every ay e

Wiring: copper (Cu)

,

Jewelry: Gold (Au), Silver (Ag), Platinum (Pt),

Light bulb: Tungsten (W)

Compounds of the transition elements are also used in many applications

Silver iodide (AgI) is a component of photographic film

Zirconium silicate (ZrSiO4) is used in artificial gemstones

Chromium (IV) oxide (CrO2) is used in magnetic recording tape

omp ex o ron e s oun n emog o n n your oo


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Ruby

Corundum

Al2O3 with Cr3+ impurities app re

Corundum

Al2O3 with Fe2+ and Ti4+

Emerald

Beryl

AlSiO3 containing Be with Cr3+

impurities


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Lanthanide series

Actinide series


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Metallic elements that have an incompletely filled

d subshells or easil become ions with incom letel

filled d subshells.

[ ] 6 226Iron Fe Ar 3d 4s

78Platinum Pt Xe 4f 5d 6s


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Metallic elements that have partially filled f

subshells.

Examples1 1 2

58

2 1 2

91

Protactinium Pa Rn 5f 6d 7s

inner transition elements are called f-block elements

The first row of f-block elements are called Lanthanide series

The second row of f-block elements are called Actinide series


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Main group elements Transition elements

Metal and non metal

Low melting and

All metal

High melting and

boiling points boiling points

Colourless Colourful

amagne c

Single oxidation state

aramagne c

Several oxidation states


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Properties of the First transition

elements


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or rans on e emen s, e ec ron eg ns o e or a

[ ] 2 1Sc Ar 4s 3d

[ ] 2 2Ti Ar 4s 3d

[ ] 2 3V Ar 4s 3d

Valence

electrons


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Sc Ti V Cr Mn Fe Co Ni Cu Zn

1 2 3 5 5 6 7 8 10 10

4s2 4s2 4s2 4s1 4s2 4s2 4s2 4s2 4s1 4s2

M3+ [Ar] 3d1 3d2 3d3 3d4 3d5 3d6

. -

filled and completely-filled 3d orbital

When the metal forms cation electrons from 4s orbital are removed first and

then from 3d orbital.


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n

When d-block elements form ions, the 4s electrons

are lost first. The number of electrons left in d subshell will be

used to refer to the t e of ion.

2 2 1 5

[ ] [ ]

2 2 2

Ti Ar 3d not Ar 4s

+ [ ]2 4 4

Cr Ar 3d referred to as d ion+

2 2Ti is referred to as d ion+

[ ]6 0r r re erre to as on

Cr Ar referred to as d ion+


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Exercise: Write the electron configuration of the

following ions:

5 3 2 3 2 3 4V ,Cr ,Mn ,Fe ,Cu ,Sc ,Ti+ + + + + + +


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As you read across a row of transition elements,

,

reaching a maximum at the group VB or VIB

, , .

These properties depend on the strength of metal

on ng, w c n urn epen s roug y on e num er

of unpaired electrons.


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Across the period

Atomic size decreases at first but then remains fairl

constant.

to an increase in effective nuclear charge

The effective nuclear char es of transition elements

change very slightly across the period, therefore the

atomic sizes are very similar


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Within the group

Atomic size increases as expected from period 4 to 5because of the adding outer shell orbital.

There is no size increase from period 5 to 6 because

of the lanthanide contraction Lanthanide contraction is the extra shrinkage that

results from the nuclear charge of the additional 14

elements. This decrease is cancel out the normalincrease between periods.


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First ionization ener

Across the period

The first ionization energies increase only slightlyacross the period

shield outer electrons from the increasing


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Within the group

Th fir t i niz ti n n r r f r l m nt

from 4th period to 5th period but then increases for

l m nt fr m th ri t th ri

The first ionization energy for elements increases

because the atomic size chan es onl sli htl but the

nuclear charge changes much more


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One o the most characteristic chemical properties

of the transition metals is the occurrence of multipleoxidation states

This multiplicity of oxidation states is due to the

varying involvement of d electrons in bonding Since ns and n-1 d electrons are so close in ener

transition metals can involve all or most of these

electrons in bonding


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The elements at the beginning (up to Mn) exhibit a highest oxidation state that

corres onds to the loss of all of the electrons in both the s and d orbitals of their

valence shell.


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Transition elements usually exhibit their highest oxidation states

in compounds with very electronegative elements such as

oxygen and fluorine

xoan ons:

3 5

4Vanadium vanadate ion VO V +

( )2 64Chromium chromate ion CrO Cr +

2 7

7 dichromate ion Cr O Cr Man anese erman anate ion MnO Mn

+

Be ond Mn the elements are stable with oxidation state of +1+2 and +3.

The +2 oxidation state is common because ns2 electrons areeasily lost.


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rans on e emen s can orm o on c on ng an

covalent bonding Ionic bonding is more common in the lower oxidation

state

Covalent bonding is more common in the higheroxidation state

2

2

4

TiCl Ti ionic solid +

+

4


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Colour and ma netic ro erties

Meta ons t at conta n parta y e or ta usua yform coloured complex ions and also show

paramagnetic property Ions with empty d orbital (d0) or filled d orbital (d10) form

colourless complexes and show diamagnetic property

3

0

Sc + 3

3

Cr + 2

7

Co + 2

8

Ni + 2

9

Cu + 2

10

Zn +

( )n

2 6solution of M H O ; M is metal

+


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o now t e terms associate wit coor ination compoun s.

To be able to obtain the oxidation state of the central metal.

To determine coordination number of a central metal atom

To name a complex ion or coordination compound given itsformula.

To write a formula of a coordination compound or complex

ion given its name.


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Coordination compounds are important for three

reasons:1. Most of the elements in the periodic table are metals,

and almost all metals form complexes

. ,

catalysts are important as a way to control reactivity

3. Transition-metal com lexes are essential in biochemistr

a. Hemoglobin, an iron complex that transports oxygen in blood

b. Cytochromes, iron complexes that transfer electrons in cells

c. omp exes t at are components o enzymes, t e cata ysts or

all biological reactions


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Coordination compound : substance that typically

contain at least one complex ion or neutral complexspecies

Examples of complex ion [Co(NH ) ]3+

Examples of neutral complex : Pt(NH3)2Cl2 and Fe(CO)5

Complex ion

CCo lNH


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Complex ion consists of a central metal cation

bonded to ligands by coordinate covalent bond Ligands : molecules or ions that have electrons to

ive to metal cation

3 6ligand


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Within a ligand the atom attached directly to the

metal through the coordinate covalent bond iscalled the donor atom.

Donor atom

H O

H H


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In 1893, Alfred Werner

explained the difference

compounds above by

re resentin their

dissociation in water.


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3+2

3 3 3 (aq)6 6 (aq)Co NH C Co NH 3C +

36 NH are gan s

en isso ve t e ye ow compoun in water, t e

total number of ions is 4 i.e. one complex ion and

t ree counter ions.

If we add an excess amount of silver nitrate(AgNO3) solution to this solution, we will obtain 3

moles of silver chloride (AgCl) as precipitate.


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2H O + 3 2 3 (aq)5 5 (aq)

o o

35 NH and 1 Cl are ligands

When dissolve the pink compound in water, the

total number of ions is 3 i.e. one complex ion and

two counter ions.

If we add an excess amount of silver nitrate(AgNO3) solution to this solution, we will obtain 2

moles of silver chloride (AgCl) as precipitate.


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The number of bonds formed by metal ions to

ligands in complex ions The coordination number of the central metal varies

,

configuration of the transition metal ion.

any me a ons s ow more an one coor na on

number, and there is no simple way to predict what

t e coor nat on num er w e n a part cu ar case.

The typical coordination number are 2, 4 and 6.

See table 2.4


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Monodentate or unidentate ligand can form one

bond to a metal ion Bidentate ligand can form two bonds to a metal ion

a metal ion


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Exam les of monodentate li ands


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Exam les of bidentate li an s


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Exam le of ol dentate li an


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A complex formed by polydentate ligands is frequently quite

stable and is called a chelate.

po y en a e gan s are o en ca e c e a ng agen s

[Co(en)3]3+ [Co(EDTA)]


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Exam les:


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The cation is written before the anion

charge of the anion(s)

,

and the whole ion is placed in brackets.

[ ]2 3 2 4K Co(NH ) Cl

[ ]3 4 2Co(NH ) Cl Cl

[ ][ ]3 4 4Pt(NH PdCl)


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. e cat on s name e ore t e an on.

3 4 2

chloride

o

tetraamminedichlorocobalt(III)the name is

anicati noon

K Fe CNpotassium hexacyanoferrate(II)the name is

ca aniontion


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. e name o comp ex cons sts o two parts wr tten

together as one word. Ligands are named first

an t e meta on s name secon .

[ ]3 4 2Co(NH ) Clthe name is tetraamminedichlorocobalt III ion

+

ligand name metal name

[ ]4

6Fe(CN)



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. e comp ete gan name cons sts o a ree

prefix denoting the number of ligands, followed

y t e spec c name o gan .

[ ]4

6Fe(CN)

Greekprefix ligand

ligand name

e gan name s exa cyano


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Li ands name

Anionic igan s en s an -o w ere t ere was an -i e

or an -ato where there was an -ate. Look:

Bromide, Br: Bromo

Carbonate, CO32: Carbonato

Cyanide, CN

: CyanoThiocyanate, SCN: Thiocyanato

Oxide, O2: Oxo

The neutral ligands keep their original names, with a few

exceptions:

Ammonia, NH3: Ammine

Carbon monoxide, CO: Carbonyl

Water, H2O: Aqua

d


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Li ands name

The prefixes mono-, di-, tri-, tetra-, penta-, and hexa- are used to

denote the number of simple ligands

Greek

[ ]

-

4

6

pre x

Fe(CN) the ligand name is hexa cyano

When the name of ligand already has a number prefix, the number

gan

of ligands is denoted with bis (2), tris (3), tetrakis (4) and so forth.

The name of the ligand is followed in parentheses.

[ ]3 3Co(en) Cl

the name is tris eth lenediamine cobalt III chloride

3ligand name

Li d


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Li ands name

When there are two or more types of ligands, the ligands are

written in alphabetical order (disregarding Greek prefixes).

3 4 2

Co NH ) C

the name is tetraamminedichlorocobalt III ion


gan amm ne s wr en e ore gan c oro

M l


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Metals name

4. The complete metal name consists of the name of

metal, followed by the oxidation number of metal asa Roman numeral in parentheses.

Co NH Cl +

cation

the name is tetraamminedichlorocobalt III ionoxidationnumber 3

M t l


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Metals name

In order to identify whether the complex ion is cation

or anion, the name of metal is ended with ate for

+

the anion.

cationthe name is tetraamminedichlorocobalt III ion

oxidationnumber 3

( )2 5anion

Co(H O) CN

the name is aquapentacyanocobaltate(III) ion

M t l


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Metals name

Where there is a Latin name for the metal, it is

usually used to name the anion.Copper (cuprum): Cuprate

[ ]4

6Fe(CN)

o aurum : ura e

Iron (ferrum): Ferrate anionthe name is hexacyano ferrate (II) ion

Lead (plumbum): Plumbate[ ]

2

2 5Fe(H O) (OH) +

Tin (stannatum): Stannate

catione name s pen aaqua y roxo ron on

Metals name


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Metals name

Oxidation number of metal ion is calculated from

the total charge of the complex minus the totalcharge of the ligands in the complex as follows;

[ ]46Fe(CN) the name is hexacyano ferrate (II) ion anion

total charge of the complex = 4

o a c arge o e gan s =

oxidation number of metal ion = ( 4) ( 6) 2 =

= +

Exercise Some Coordination Com lexes


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Exercise: Some Coordination Com lexes

molecularformula

Metal ion Liganddonoratom

coordinationnumber

[ ]3 2Ag(NH ) +

[ ]24Zn(CN)

[ ]2

6PtCl

[ ]2

3 6Ni(NH ) +


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1. What is the systematic name of [Co(NH3)3Cl3]?

2.

What is the systematic name of [Co(en)2Cl2]NO3?3. What is the formula of

tetraamminebromochloroplatinum(IV) chloride?

4. What is the formula ofhexaamminecobalt III tetrachloroferrate III ?


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ruc ures an somer sm n

coordination com ounds


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Coordination number

2 4 4 6


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Isomers are two or more

species which have the Two isomers of Co NH Cl +same formula but exhibit

different properties

The different propertiesare the result of different

arrangements of atoms.


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In order to be isomers, the two compounds

must: contain the same number and types of atoms, and

- .


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Structural isomerism: the isomers contain at least one

different connection or bonding.

in the isomers are the same but the spatial. .

different 3D-structure)


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Linkage isomerism:

The composition of the complex ion is the same but the pointof attachment of at least one of the ligands differ

Ligands that can attach to metal ions in different ways are

thiocyanate (SCN), cyanide (CN), and nitrite ion (NO2).

( ) ( )3 24 Co NH NO Cl Cl

tetraamminechloro cobalt(III) chloride (yellow)nitrito-N

4

tetraamminechloro cobalt(III) chloride (red)nitrito-O


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Ligands That Can Form Linkage Isomers

CN cyanide ion C or N

SCN thiocyanate

ion S or N

NO nitrite ion N or O


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eometr ca somer sm or c s-trans somer sm:

Atoms or groups have different positions around the

metal atom


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Optical isomerism :

Optical isomers are isomers that are non-superimposable

mirror images of one another.

O tical isomers3+


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[Co(en)3]

3+


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Optical isomerism :

Isomers which rotate plane-polarized light inopposite directions with the same angle.


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the object and its mirror image are identical, it is

called achiral.

object whose mirror image is not identical with itself

is said to be chiral


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trans-isomer is achiral : diastereomers

cis-isomers are chiral : enantiomers


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Bonding in Coordination compounds


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e orma on o coor na on cova en on n a

complex,

a ligand orbital containing two electrons overlaps an

unoccupied (empty) orbital on the metal ion.


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or coor nat on num er

2 ligands need 2 hybrid orbitals to share electrons with the

3


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or coor na on num er


For d10 ion, the complex form tetrahedral geometry


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2 3


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For coordination number 6


meta atom

Consider octahedral complex of Fe2+ ion


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3 44 4d ps d

2

ionFe

+

4 4d3 4 4p

d s d

sp

3 4 4

d s d

2 3d sp

4p 4d3d 4s 4d


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2

sp

+

2 6

4p3d3d 4s 4d

4

sp

6


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-


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Octahedral complexes

The two of the orbitals, dz

2 and dx

2

-

2 , point their lobes

directly at the point-charge ligands.

The other three orbitals, dxy, dyz, and dxz , point their lobes

between the point charges.


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s s sp ng o e or a energ es(symbolized by ) that explains the colour and

ions.

-


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The splitting of d orbitals determine the

arrangement of electrons in these orbitals.

Electrons occupy orbitals singly as long as empty

The repulsive pairing energy (Epairing) must be

orbital.


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d4

dz dx - y2 22

dz dx - y2 22 small

large

xy xz yz dxy dxz dyz

high sp in com p lex lo w sp in co m p lex


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e e 6- on s nown to ave one unpa re

electron. Does the CN- ligand produce a low-spin or

ig -spin case


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From studies of many octahedral complexes, The

ligands are arranged in order of decreasing values toward a given metal as follows:

2 3 2O> CN > NO >en > NH > H O> OH > F > Cl > Br >Istrong fiel dlarge

wea

k fi el ds mall


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Predict the number of unpaired electrons in the

[Cr(CN)6]4-


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e -or a sp ng s oppos e o a oroctahedral arrangement

None of 3d orbitals point

their lobes directl at the

point-charge ligands. Thus the

splitting of d-orbitals in

tetrahedral arrangement is

smaller than in octahedral

Only high spin complexes

.

are observed


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2z

d 2 2x yd

d d doct

e

xz yz xy 2z2 2x y

Octahedral case Tetrahedral case


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Give the crystal field diagram for the tetrahedral

complex ion of CoCl42-


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Square Planar complex Linear complex

Only low spin complex have

been found


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Use crystal field theory to describe the d-electron

distributions of the complexes

( ) ( )2 2

3 4 4Ni NH and Ni CN

+

The tetraamminenickel(II) ion is paramagnetic, ande e racyanon c e a e on s amagne c.


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The complex ion shows colour because it absorbs certain wavelengths of light

in the visible region, the colour of that substance is determined by the

wavelengths of visible light that remain.


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Relation between absorbed and observed colours

The reason that the ion absorbs specific wavelengths of visible light


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( )3

3 1

2 6Ti H O is violet, Ti d ion

+ +

2

z

d 2 2x y

d

2zd 2 2x yd

h

xz yz xy xz yz xy

3

Ground state+ 3

Excited state+

2 6Ti H O

2 6

Visible s ectrum of Ti H O 3+


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The or E ener s acin in the molecule relates to thewavelength of light by

1


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If the chan es the of li ht to be absorbed chan es

, =

therefore the colour changes.

Since the li ands coordinated to a iven metal ion determine

the size of d-orbital splitting (), the colour changes as the

ligands are changed.

2 3Cr H O Cl Violet

Observed colour

( )2 25Cr H O Cl Cl Blue-green

( )2 24Cr H O Cl Cl Green

2 3 2

st r ong fi el dC O > C N > N O > en > N H > H O >

weO H > F >

ak fCl > Br > I

i e l dt r on g fi el dlarge

we

ak f

ie lds ma ll


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i ht b b d b l ith diff t li dight absorbed by complexes with different ligands


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Colour of Complexes with different ligands


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Documents

2. Transition Metals