Transition metal

TRANSITION ELEMENTS
Dr. T. Geetha
Assistant Professor
Department of Chemistry
St. Mary’s College, Thrissur

Transition Elements
❖Partially filled d orbital in its atom in the ground state or in any
one of its oxidation state
❖General Electronic configuration (n-1) d1-10ns1-2
❖Zn , Cd & Hg – Group 12 - pseudo transition elements – filled d
orbital (n-1) d10ns2 / (n-1) d10
Transition Metal – Dr. T. Geetha, St. Mary’s College, Thrissur

What is a transition metal?
“an element with valance d- or f-electrons”
ie. a d-block or f-block metal
d-block: transition elements
f-block:
inner transition elements
3d
4d
5d
6d
4f
5f

What’s interesting about Transition
Metal Complexes??
color
geometry
coordination
number
magnetic behavior
oxidation states
biological
activity
medical
applications

The 3d series
➢Starts from Scandium & ends in Zinc
➢Atomic no. - (21-30)
➢ Electronic configuration: [Ar]3d14s2 to [Ar]3d104s2

Orbital Occupancy of the Period 4 Transition Metals
The number of unpaired electrons increases in the first half of the
series and decreases in the second half, when pairing begins.
Extra stability of
half filled &
completely filled
orbital

The 4d series
➢ Starts from Yttrium & ends in Cadmium – (39-48)
➢ Electronic configuration: [Kr]4d15s2 to[Kr]4d105s2
➢ Mo - stability of half filled shell
➢ Ag - stability of completely filled shell
➢ Other anomalies explained by
▪ nuclear electron attraction
▪ Shielding of electron
▪ Inter electronic repulsion etc.

The 4d series
Element Atomic Number Symbol
Electronic
configuration
Yttrium 39 Y [Kr] 4d15s2
Zirconium 40 Zr [Kr] 4d2 5s2
Niobium 41 Nb [Kr] 4d4 5s1
Molybdenum 42 Mo [Kr] 4d5 5s1
Technetium 43 Tc [Kr] 4d5 5s2
Ruthenium 44 Ru [Kr] 4d7 5s1
Rhodium 45 Rh [Kr] 4d85s1
Palladium 46 Pd [Kr] 4d105s0
Silver 46 Ag [Kr] 4d105s1
Cadmium 48 Cd [Kr] 4d105s2

The 5d series
➢Starts from Lanthanum & ends in Mercury (57-80)
➢ Electronic configuration: [Xe]5d16s2 to [Xe]4f145d106s2
➢Lanthanide elements (4f series) lies between La & Hf
➢Au - stability of completely filled shell
➢Pt - 5d96s1 – no simple explanation

The 5d series
Element Atomic Number Symbol
Electronic
configuration
Lanthanum 57 La [Xe] 5d16s2
Hafnium 72 Hf [Xe] 4f145d26s2
Tantalum 73 Ta [Xe] 4f145d36s2
Tungstun 74 W [Xe] 4f145d46s2
Rhenium 75 Re [Xe] 4f145d56s2
Osmium 76 Os [Xe] 4f145d66s2
Iridium 77 Ir [Xe] 4f145d76s2
Platinum 78 Pt [Xe] 4f145d96s1
Gold 79 Au [Xe] 4f145d106s1
Mercury 80 Hg [Xe] 4f145d106s2

The 6d series
➢Starts from Actinium & ends in Copernicium (89-112)
➢Electronic configuration: [Rn]6d17s2 to [Rn] 5f146d107s2
➢Actinides elements (5f series) lies between Ac & Rf
➢Rg - stability of completely filled shell 6d107s1

The 6d series
Element Symbol At. No. Electronic configuration
Actinium Ac 89
6d–orbitals
are filled up
[Rn] 6d17s2
Rutherfordium Rf 104 [Rn] 5f146d27s2
Hahnium Ha 105 [Rn] 5f146d37s2
Seaborgium Sg 106 [Rn] 5f146d47s2
Bohrium Bh 107 [Rn] 5f146d57s2
Hassium Hs 108 [Rn] 5f146d67s2
Meitnerium Mt 109 [Rn] 5f146d77s2
Ununnilium Uun 110 [Rn] 5f146d87s2
Unununium Uuu 111 [Rn] 5f146d97s2
Unubium Uub 112 [Rn] 5f146d107

Properties of the Transition Metals
All transition metals are metals, whereas main-group elements in
each period change from metal to nonmetal
Many transition metal compounds are colored and paramagnetic,
whereas most main-group ionic compounds are colorless and
diamagnetic
The properties of transition metal compounds are related to the
electron configuration of the metal ion
.

Metallic character
➢All transition elements are metallic in nature
➢Metallic & covalant bonding
➢Valence S electron – metallic bond
➢ (n-1) d electron- covalent bond
➢Lustre & ductility,
➢ malleability, high tensile strength
➢ thermal & electrical conductivity
➢Hard & brittle – partially filled d orbital - covalent bonding between metal atom through
orbital overlap
➢Zn, Cd & Hg – completely filled (9n-1)d orbital – lack covalent bonding through orbital
overlap - lower hardness & brittleness

Melting & Boiling Point
➢Melting & Boiling point higher than S Block element
➢Reason - valence & covalent Bond
➢Expected trend – increases with increasing no. of unpaired d electron
➢Anomalies – Mn – low M. Pt. - inherent stability of 3d54s2 - lowers
participation of these electrons in interatomic metallic & covalent bond
➢Zn, Cd & Hg –– no partially filled d orbital for covalent bonding – low M. P &
B. P

➢4d & 5d - larger, more diffuse, more penetrating than 3d orbital
➢Reduced mutual repulsion between electron – stronger bond
➢Extensive metal Metal- metal covalent bond
➢M.P. & B.P. increases as we move down a group in transition metal

Relative size of d orbitals
3d, 4d, 5d

Atomic & Ionic radii
➢Atomic & ionic radii decreases on moving from left to right
➢Atomic no. increases - Addition of new electrons in d subshell
- effective nuclear charge increases
- shielding of d electron ineffective
➢electrostatic attraction between nucleus & outermost electron
increases
➢Towards end of series – slight increase in radii
➢Atomic radii increases down a group
➢radii of 4d & 5d series nearly identical – lanthanide contraction

Atomic radii

Ionic radii

Lanthanide Contraction
As the atomic number increases, each succeeding element adds
❑one electron in the 4f orbital
❑one proton in the nucleus
❑4f electrons are ineffective in screening the outer electrons from
the nucleus causing imperfect shielding
❑gradual increase in the nucleus attraction for the outer electrons
❑gradual decrease in size occur

Density
➢Increase in density across a series
➢Dec. in atomic radii – dec. in volume – inc. in atomic mass
➢Density higher than s & p block element
➢Density of 5d series > 4d series
➢Atomic mass increases considerably on moving from second to third row but
atomic size is nearly the same – lanthanide contraction – increase in density

Density

Ionization energy
➢Ease with which an electron can be removed from an isolated gaseous
atom
➢ Ionization energy fairly high
➢Intermediate between S & P block element
➢Ionization energy increases along a series
➢increase in the nuclear charge - shielding effect of the added
electrons increases - decrease the attraction due to the nuclear
charge-opposing factors - gradual increase in the ionisation energies

Ist ionization energy

Ist ionization energy
➢energy needed to remove 4s electron - 4s electrons the
outermost electrons – higher energy - removed first
➢5d-series much higher than 3d and 4d series -5d-series elements after
lanthanum (La) - electrons go inner 4f orbital - poor shielding effect -
outermost electrons experience greater nuclear attraction - higher
ionization energies for the 5d- series
➢Values for Zn, Cd & Hg – sudden increase – additional stability due to
complete filling of d sub shell

IInd & IIIrd Ionization energy

IInd & IIIrd ionization energy
• IInd ionization energy – Cr & Cu higher – outer electronic
configuration of singly charged Cr & Cu Ion - d5& d10 - extra stability
of half filled & fully filled orbital
• IIIrd ionization energy – markedly higher - energy required to remove
a 3d electron (both 4s electrons have been removed - greater
difficulty for the removal of an electron form Mn2+ (d5) and Zn2+ (d10)
ions - marked difference between third ionization enthalpies of Fe
and Mn

Oxidation state
➢Variable oxidation state
➢(n-1)d & ns electron – comparable energy – participate in bonding
➢Varying no. of (n-1)d electron participate in bonding
➢Highest oxidation state observed in combination with F & O – Mn2O7
➢Lower oxidation state - ns electron participate in bonding
– ionic bond
➢Higher oxidation state – ns & (n-1)d electron take part in bonding
– covalent bond - charge on cation increases
– size decreases – polarizing power increases
– increases tendency of cation to share electron
➢VCl2 , MnCl2 - Ionic; VCl4 ,MnCl4– Covalent

Oxidation state
+2

Oxidation state
➢+2 - Most common oxidation state
➢+3 - oxidation state shown by all elements except Cu & Zn
➢+1 - oxidation state shown by Cu
– unstable in aq. solution – disproportionation
- stability of Cu2+ in aq. solution- higher hydration enthalpy of
Cu2+

Oxidation state
➢For the first Five elements
➢ minimum oxidation state = no. of electron in the outer s subshell
➢Maximum oxidation state= sum of outer s & d electron
➢For the rest
➢minimum oxidation state = no. of electron in the outer s subshell
➢Maximum oxidation state – rarely higher than +2 or +3
➢Elements with greatest no. of oxidation state – middle of series
➢Elements with highest oxidation state – middle of series
➢Mn – maximum oxidation state & highest in 1st series (+2 to +7)

Oxidation state
➢Elements in the beginning of series - fewer oxidation state – fewer
d electron – Sc (+3), Sc(+2)- rare; Ti(+2), Ti (+3), Ti(+4) – more stable
➢Elements towards end of series - fewer oxidation state – Too many d electron
- fewer d orbital with unpaired electron – Zn (+2), Cu(+2), Cu (+1) only
➢Oxidation state of elements differ by unity – V(+2), V(+3), V(+4), V(+5)
➢Highest oxidation state in 3d series – (+7) - Mn
4d series – (+8) - Ru
5d series – (+8) – Os
➢Oxidation state of metal - Zero – Ni(CO)4 , Fe(CO)5 & Cr(CO)6

Oxidation state
➢ Among Group 4 to 10 – higher oxidation state favoured by heavier members –
Group 6 – Cr, Mo & W - , Mo (+6) & W (+6) more stable than Cr(+6) – Cr2O7
2- -
strong oxidizing agent in acidic medium – MoO3 & WO3 are not
➢P block elements - Lower oxidation state favoured by heavier members – inert
pair effect
➢Higher oxidation state – covalent character – increase in acidity of oxides &
halides
MnO Mn2O3 MnO2 Mn2O6 Mn2O7
(+2) (+3) (+4) (+6) (+7)
Oxidation state
Covalent character
Acidic character

Reducing property & Electrode potential
➢ more negative the reduction potential for Mn+/M couple – greater reducing
potential – greater tendency of metal M to undergo oxidation
➢E0
M
2+
/M values for all 3d transition metals except Cu are negative
➢All 3d metals except Cu will reduce H+ & displace H2 from dil.acid
➢Some react too slowly
➢Some coated with adherent protective layer of oxides – protect from attack by acids
➢Less negative E0 , lower reducing character – across series

Reducing property & Electrode potential

Factors determining E0 Values & reducing character
➢ Value of E0
M2+/M determined by
➢Enthalpy of sublimation – ΔsubH0
➢First ionization energy – IE1
➢Second ionization energy- IE2
➢Enthalpy of Hydration - ΔhydH0
M(s) M(g) M+(g) + e-
M2+(aq) M2+(g) + e-
ΔsubH0
ΔhydH0
IE1
IE2
ΔsubH0 - positive – energy consuming
IE1 - positive – energy consuming
IE2 - positive – energy consuming
ΔhydH0 - negative – energy releasing
Lower the value of ΔsubH0, IE1 , IE2; More negative value of ΔhydH0
- More negative the value of E0
M2+/M - More reducing the metal

E0 Values & reducing character
• In general across a series –
➢First & second ionization enthalpy increases
➢Less negative E0
M2+/M values – lower reducing character
Anomalies
➢Mn higher reducing property than Cr – higher stability of half filled d5 configuration of
Mn2+
➢Zn higher reducing property than expected – higher stability of half filled d10
configuration of Zn2+
➢Ni higher reducing property than expected – most negative value for the ΔhydH0 forNi2+
in the first transition series
➢Cu – only positive value for E0
M2+/M in Ist transition series – tendency to oxidize to M2+
least - [ΔsubH0+ IE1+IE2] > ΔhydH0

Magnetic property
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+

Magnetic property
Greater the no.of unpaired e- –
more paramagnetic the ion

Magnetic property
➢Unpaired electron -
➢ magnetic moment = spin angular momentum + orbital angular momentum
➢For 3d series - magnetic moment = spin angular momentum
- Contibution of orbital angular momentum quenched by fields
associated with surrounding ligands
➢ Magnetic momentum μ = √n(n+2) (spin only formula)
➢ n = no. of unpaired electron
➢ Unit - Bohr Magneton (BM)
➢ A single 1s electron has a magnetic moment of 1.73 BM (1 BM = 9.2732 × 10-24
A m2 ).

Magnetic property
Ion Configuration Unpaired
electron
Calculated Observed
Sc3+ 3d0 0 0 0
Ti3+ 3d1 1 1.73 1.75
Ti2+ 3d2 2 2.84 2.76
V2+ 3d3 3 3.87 3.86
Cr2+ 3d4 4 4.90 4.80
Mn2+ 3d5 5 5.92 5.96
Fe2+ 3d6 4 4.90 5.3-5.5
Co2+ 3d7 3 3.87 4.4-5.2
Ni2+ 3d8 2 2.84 2.9-3, 4
Cu2+ 3d9 1 1.73 1.8-2.2
Zn2+ 3d10 0 0 0

Formation of coloured ion
➢transition metal ions are coloured due to d-d transitions
➢energy absorbed in excitation of an electron from a lower energy d orbital to a
higher energy d orbital corresponds to the frequency which generally lies in the
visible region
➢ The colour observed corresponds to the complementary colour of the light
absorbed
➢ The frequency of light absorbed is determined by the nature of ligand

➢In the presence of ligand – degeneracy of d orbital lost
➢d orbital split into different levels
➢Electron from lower energy d orbital exited to higher energy orbital
➢Absorbtion of light correspond to visible region
➢Coloure observed – complementary colour of light absorbed
➢d-d transition in symmetrical octahedral environment – not allowed –
forbidden – colour not intense
➢ Laporte rule - applies to centrosymmetric molecules (those with an
inversion centre - those that only involve a redistribution of
electrons within a given subshell are forbidden (Δl = 0)
➢ tetrahedral - lacks centre of symmetry - d-d transition allowed –
intensely coloured

Relation Between Absorbed and Observed Colour

Splitting of d-orbital energies by an octahedral field of ligands
D is the splitting energy

Colour of aquated first row ion
Ion Configuration Unpaired electron Colour
Sc3+ Ti4+ 3d0 0 Colourless
Ti3+ V4+ 3d1 1 Blue /purple
V3+ 3d2 2 green
V2+ Cr3+ 3d3 3 violet
Mn3+ 3d4 4 violet
Mn2+ /Fe3+ 3d5 5 Pink/ yellow
Fe2+ /Co3+ 3d6 4 Green/ Pink
Co2+ 3d7 3 pink
Ni2+ 3d8 2 Green
Cu2+ 3d9 1 Blue
Zn2+ Cu+ 3d10 0 Colourless

Complex formation
➢Large no. of complexes
➢Capacity to accept electron pair from ligand
➢Small size of transition metal
➢High ionic charge – high charge density – easier to accept electron
➢d orbital available for bonding
➢[Fe(CN)6]3- [Fe(CN)6]4- [Cu(NH3)4]2+ [Cu(H2O)6]2+

Catalytic properties
➢show catalytic activity
➢ability to exhibit multiple oxidation states
➢to form complexes,
➢alloys and interstitial compounds
➢Chemisorb reactant molecule
Reactant + Catalyst Activated surface complex
Products + Catalyst
➢Pathway causes
➢Increase in conc of reactant at catalyst surface
➢Lowers activation energy – weakening of bonds in reactant

Catalytic properties
➢heterogeneous catalyst used in car exhausts- Pt/Rh alloy supported
on a ceramic matrix and converts the mixture of O2, CO, NOx and
hydrocarbons in the exhaust gases to H2O, CO2, and N2
➢V2O5 - Contact process - manufacture of sulphuric acid,
➢ finely divided iron - Haber’s process - manufacture of NH3
➢Ni - hydrogenation of oils

Non stoichiometric compound
• Form Bertholides
➢do not correspond to ideal chemical formula
➢ different elements are in non integral atomic ratio- VH0.56, TaH0.76,
➢Do not correspond to normal oxidation state of component element
➢Due to defect in crystal lattice & variable valency of metal
➢Small atoms like H, N etc trapped in voids
➢Hard, inert, high M.Pt. than metal
➢Most have formula – WO3-x, Co1-xO x- positive smaller than 1

Non stoichiometric compound
• Fe1-x O - Fe0.95O
➢Metal deficiency defect – FeO crystal – Fe2+ ion lost – electrical
neutrality maintained by converting Fe2+ to Fe3+
Zn1+δO -
➢Metal excess defect – Excess Zn 2+ ion trapped in interstitial site–
electrically neutral - free electron in neighboring site – absorb
light – yellow colour

Alloy formation
➢Homogenous substitutional solid solution
➢ distribution – random or ordered
➢Alloy formation favoured between
➢ Comparable metallic radii
➢ Comparable electronegetivity
➢ Cu/Au, Ag/Au, Cu/Ni
➢Alloys -hard – high mp - useful

Difference Ist & other row elements
➢Atomic size – Ist row lower – IInd & IIIrd row similar
➢Reactivity - Ist row – more reactive
➢Stability of oxidation state - Ist row - +2 & +3 more important
• - IInd & IIIrd row - higher oxidation state
➢Coordination no. - Ist row - rarely greater than 6
• - IInd & IIIrd row - many complexes with coordination
no. greater than 6
➢Type of complex - Ist row - high spin complexes more
• - IInd & IIIrd row - high spin complexes few, more low
spin complxes

Reference
• B.R. Puri, L.R. Sharma and K.C. Kalia, Principles of Inorganic Chemistry, 31 st
Edition, Milestone Publishers and Distributors, New Delhi, 2013
• P.L. Soni and Mohan Katyal, Textbook of Inorganic Chemistry, 20th Edition, S.
Chand and Sons, New Delhi, 2013
• Wahid U. Malik, G.D. Tuli and R.D. Madan, Selected Topics in Inorganic Chemistry,
S. Chand and Co., New Delhi, 2010 (Reprint)
• J.E. Huheey, E.A. Keitler and R.L. Keitler, Inorganic Chemistry – Principles of
Structure and Reactivity, 4 th Edition, Pearson Education, New Delhi, 2013

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