3d series Transition Elements for B.Sc. IV sem

3d series Transition Elements for B.Sc. IV sem

1. INORGANIC CHEMISTRY-IL BSCCH-201

UNIT 1: CHEMISTRY OF THE ELEMENTS OF
FIRST TRANSITION (3-d) SERIES

1.1 Objectives

12 Introduction
1.3 Characteristic Properties of d-Block Elements
1.4 Properties ofthe Elements of he First Transition series

1.5 Binary Compounds and

17 Coordination number and Geometry

1.8 Summary
19 Terminal Questions

1.10 Answers

11 OBJECTIVES

The objective of writing th text material of his uni sto acquaint the readers o the

characteristic properties of the block elements, in general, such as ihr general

electronic con

on and variable oxidation states, complex formation tendency

magnetic properties, formation of coloured ions/compounds, cat

activity, et

and periodic properties, vis, atomic rai,

mic volume, ionic adi, melting and

boiling points, ionization energies and reactivity, standard electrode potentials and
reducing properties ec. along with their periodi variation along the series. Ii also

aimed at throwing light on the above properties of the first transition series, in

particular, to illustrate the relative stability ofthe oxidation states of these elements
along with to discuss the coordination number and geometry oftheir complexes and

binary compounds of these elements

1.2 INTRODUCTION

“The d-biock cements have been defined as “the elements whose am

y
shell, The deblock elements are alo called the transition elements or metals. This ás

sive the lst électron in the d-subshell belonging to the penultimate or (

because they exhibit gradual transitional behaviour between hi

ly reactive s-block

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(lectropositive) and p-block (clectronegativ) elements, ic. their properties have
been found to be intermediate between those of the s-block and p-block elements
Thus these elements are located in the middle of the periodic table and are the
members of the Groups 3 to 12 (IIB 10 VII 19 I B) in the modem periodic table
According to IUPAC defiiton, “a transition element is an element which has an

incomplete dsubshell in ether neural atom or in ions in chemically significa (or

common) oxidation state". According to this definition zine (Zn), cadmium (Ci) and
mercury (Hg) are excluded from the list of transition elements as they nether have
party filled de

ubshell in their atoms or ions nor they show the u

al properties of

twanstion elements to an appreciable extent Still in order 10 rationalize the

classification of elements, they are studied along with oer «block elements

“There ae four series of elements which constitute the block elements. Each series

‘comprises ten elements as given below:

1. Elements of the First Transition series or 3d-Transition series: The elements

from scandium (Se, Z= 21) to Zine (Zn, Z = 30) form he series.

2. Elements of the Second Transition series or 4d-Transit

series: This series

consists ofthe elements from yttrium (Y.

39) to cadmium (CZ

=.

3. Elements ofthe Third Transition series or Sd-Transition ser
lanthanum (La, 2= 57) and haa

«The elements

m (Hf, Z= 72) 10 mercury (Hg. Z = 80) constitute

‘S4-Transton series,

4. Elements of the Fourth Transition series or 6d-Transtion series: The elements
89) and rtherfordvm (RF

actinium (Ae 104) 10 copericum (Ca, Z= 112)

are the members ofthis series. All these elements ae radipoaciv and do not occur

in nature, These have been artificially made inthe laboratory.

13 CHARACTERISTIC PROPERTIES OF D-BLOCK
ELEMENTS

Some of the important characteristics of the dblock elements are summarized as

follows:

e Oxidation States

13.1 Electronic Configuration and Va

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The d-block elements have a valence shell electronic configuration of (a-Dd" "ns"

‘where (01) stands for ier shell whose orbital may have one wo ten electrons and
the sorbials of the outermost shel () may have no electron or one or two eletrons.
‘The filling of d-orbital takes place after the s-orbital of next higher shell has already
filed as has been discussed in Aufbau principle in Unit 1 (BCH-101). This is because
Ins orbitals have lower energy than (n-Did orbitls. But during ionization of the
elements (oxidation), the electrons are first lost from as level followed by the

expulsion from (n-1J4 subshell (devi

Ion from the expected behaviour) because (n-
sell once

DA subshell becomes of the lower energy than ns

filing of

clectrons commences in (n-1» subshell

Most of the d:block elements show several oxidation states (variable) in their
‘compounds due othe availability of electrons in the valence shell which comprises

of the two subshells, » aber in

„(MD and ns whose orbitals are quite close to

energy and hence the electrons can be used from both the subshells for bonding and
ons can be used by them. The
m both

under different conditions diferent number of ele

variabiliy inthe oxidation states increases towards the middle of the series I
end, i. left —» middle — right. I has been observed thatthe dblock elements can
form ionic bonds in thet lower oxidation states and the ioc character of the Bond

decreases as well asthe covalent character increases wi

increasing oxidation state
‘As a result, with decreasing ionic character the acidic character of the oxides and

chloride increases

1.32 Complex Formation Tendency:

‘The cations of block elements are unique in their tendency to form complexes with
several molecules such as ammonia, water, et. or different ions such a eyanide, NO
>, halide ions, ete, These molecules or ions are calle ligands, The complex forming

tendency ofthese elements is atributed to the following factors:

(a) Small size and high positive charge density,
(®) Availability of vacant dorbital of right energy 10 accept the lone pairs of
electrons from the approaching ligands,

(6) Exhibition of variable oxidation state.

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The detailed account of this tendency will be given in the respective sections

mentioned ahead.

1.3.3 Magnetic Properties

Many compounds of d-block elements exhibit magnetic properties. Qualitaively
speaking, here are several kinds of magnetism. The substances which are weakly
repelled by the strong magnetic field are termed as diamagnetic whi
are weakly atracted by the strong magnetic Mel are called paramagnetic. Thes

substances lose their magnetism on removing the magnetic field. Diamagnetism is the

€ those which

property of the completly fille electronic subshlls and is shown by all substances
10 more or less extent. Paramagnetism is produced by the presence of unpaired
électrons and because most of the d-block metal atoms and ions have unpaired

clectrons, they are paramagnetic in behaviour

In some tan:

ton metals (eg. Fe, Co, Ni) unpaired electron spins are more
‘Pronounced and show much more paramagnetism than the ther «block metals. Such
‘metals are called ferromagnetic metals and magnetic property shown by them is
agnetized, The detailed

‘known as ferromagnetism, Such metals can be permanenily

account will be given inthe section LA ofthis unit and in subsequent unis

1.34 Formation of Coloured lons/ Compound:

‘The majority of compounds of deblock elements, whether onic or covalent, are

coloured in solid or solution state. This property of d-block elements is in marked

difference from those of sor p-block elements which are white or light coloured.

‘The colour ofa substance arises from the property of he substance o absorb light of
certain wavelength in the region of visible light (white light) when ho later interacts
‘with he substance, The colour of the substance is he colour of the transmitted light
component and is complementary to the colour of light component absorbed. The

colour of d-block metal ons is associated with

(a) an incomplete dsubshell in the metal ion

(the nature of surounding groups around the metal on,

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The whole act ol exhibition of colour by block ons/compounds can be explained as

follows. In a free gaseous or isolated ion the five d-oritls are degenerate, ie. of

same energy. Since five orbitals are oriented differently in space, the surrounding
groups affect the energy of some orbital more than others inthe compounds. This

destroys their degeneracy. For example, in

simplest case of an octahedral

‘comple, they form two groups of orbital of ifferer

CES

Maman nes fg

Fig. 11 Bars centre

‘Thus, in block metal ions with partially filed d-subshll, i is possible 1 promote

electron) from one set of d-obitals to another st (group) of higher energy by fairy

energy absorbed from the visible light. The colour of the compounds depends
on the energy difference (gap) between the two groups (sets) of d-orbitls. This in
turn depends on the nature of ligands and ther arrangement around the metal ion in

the compound / complex.
135 Catalytic Activity

‘The catalytic activity of block elements and their compounds is associated with
their variable oxidation states and ther capability of form

A number of d-block metals and their compounds are known to catalyse

d compounds.

reactions of industrial importance, e.g. vanadium (V) oxide in the manufacture of

sulphuric acid by contact process, etc. An important view of the mechanism of

catalysis is that at solid surface ofthe catalyst, bonds would be formed between
molecules of the reactants and atoms of the catalysts thereby increasing the
concentration ofthe reactants atthe surface. This weakens the bonds ofthe reactant

‘molecules due to lowering ofthe activation energy.

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13.6 Formation of Interstitial and Non-stoichiometric Compounds:

‘The d-block elements form inte such

à compounds with small non-metal at

as H, CN, B, Si et. due 10 the ability of metal lance 10 accommodate these non-

‘metal atoms between the metal atoms without distortion of struct

(One of the striking properties of these metals is ıhe formation of non-stoichiometric

compounds which often exhibit semicondu

ivi, Muorescence and behave as
heterogeneous catalysts. This non-stoichiomery is due to the defects in the solid

13.7 Metallic Character and Alloy Formation:

All the d-block elements are metals, good conductors of heat and electricity, are

malleable and ductile. All are solids except Hg (mercury) which exists as liquid at

ordinary temperature

‘These metals form alloys with each other due 1 almost similar sizes of the atoms,
Thus the atoms of one metal can easily take up positions in the crystal lace of the
other. The alloys are usually harder and have higher melting points than the parent

‘metals, are more resistant to corrosion than their constituent

38 Periodie Properties and Their Variation along the Series:

‘The atomic adi, stomic volumes, ionic ra

noting and boiling points, ionization
energies and reactivity, standard electrode potential and reducing properties, et. are
the important periodic properties of the d-block elements which vary and have a
<efinite trend, in general, along each series. These willbe discussed below

a) Atomic Radii, Atomic Volumes and Tonic Radi

‘The atomic radii generally decrease, with a few exceptions, on moving from left to

right in each series ofthe transition elements due to increased mueca

step and constant value of the azimuthal quantum number (ie. 1) rec

electron,

The d-block elements have low stomic volumes as compared 10 those of the

‘neighbouring s- and p block elements. This is due to the fact that in these element

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(0-1) d-subsbells are being filed and he increased nuclear charge pulls he electron
cloud inwards

The ionic radi ofthe deblock elements follow the same tend as the atomic radi, i.
the radi ofthe ons having the same charge decrease with increasing atomic number,

“These properties willbe discussed in detail for every series.
b) Melting and Boiling Points

“The melting and boiling points of these elements are generally very high showing that

they are held by strong forces. The melting and boiling points have the high
in the middle of the series because, perhaps these elements have the maximum

ber of unpaired d-clectrons available for bonding, detailed account of which will

be given ahead for every series.

© Tonization Energies and Reactivity

‘The ionization energy values of the diblock elements are fairly high and lie in
between those of s- and p-block elements, Le. these elements are les cletropositive
do

not form ionic compounds as readily as s-block elements and form covalent

than block elements and more so than p-block elements. Hence, these len

‘compounds as well. Because of the existence of covalent bonding, they have high
h

us of sublimation, Le a large amount of energy is required 10 convert them from

solid to vapour state The metal ions also do not get hydrated easily. Due to these

parameters, the metal ions have a small tendency to react. Examples will be given in

each series
4) Standard Electrode Potentials and Reducing Properties

The standard reduction potential values of transition elements are generally lower
(negative) than that of the standard hydrogen electrode (taken as zero). Thus they

evolve He gs from acids though most of them do that at low rate.

These metals are poor reducing agents which are contrary 10 the expected behaviour
because of the high heats of vaporisaion, high ionization energies and low heats of

Inydration. Example, ¡available will be given in each series

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1.4 PROPERTIES OF THE ELEMENTS OF FIRST
TRANSITION SERIES

‘As has already been mentioned inthe beginning that he first transition series is also
known as 3dseries because the last or the differentiating electron in the atoms of
these elements enters the 3dsushell. This series stars at scandium, he element of

Group 3 and ends at zine, the element of Group 12, containing a toa often elements.

Thus, his series of elements lies in between calcium (Ca, Z=20) and gallium (Ga,
2231) the elements of Group 2 and Group 13, The ten elements ofthe first transition
are scandium (Sc, 2221), 6 22), vanadium (V, 2223), chromium

7-24), manganese (Mn, Z=25), iron (Fe, Z= 26), cobalt (Co, Z= 27) nickel Ni

nium (Ti, Ze

2-28), copper (Cu, Z= 29) and vine (Zn,

7= 30). These elements are much more

important than those of second transition series. Al the characteristics properties of
the block elements are shown by the elements of first transition series which are

given below
1.4.1 Electronic Configuration and Variable Oxidation States.

‘The genera valence hell electronic configuration ofthese element is 30'4 where
=I t0 10 and y= 1 or 24. the 3d subshll has one to tn electrons from Se to Zn
and bah in general, has two electrons (ie. 4) except in
econ (ie ds). The ex
and Cu is atrbuted to the exchange energy effect and the extra stability of the
resukinghalf-filled and completly-filed subshells. “The siting of an electron
fiom one subhell 1 another of similar or slightly higher energy in order to achieve
the al

and Cu which

have only one 4s

onal valence shell configuration of Cr

ed or completely filed subshell is known as exchange energy effect”

“The state of affairs can be shown as follows:

cr

24): Sas? expected ba unstable) — 30 cual, mor stable)

Cu 2-29): 38/4 (expected but unstable) —» 34%! (actual, mor sable)

‘As evident, there i exchange of elctrons from 4s to 3d subshel thereby increasing
the stability of the valence shell configuration in Cr and Cu atoms. Thus, among 34

series elements, only Cr and Cu exhibit iegular‘anomalous electronic

configurations.
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The is transition serie elements generally show variable (many) oxidation states in
their compounds / nie forms. The cause of showing different oxidation stats is that

these elements have seve

34 electrons which are quite close to 4s ~ electrons in
energy. The minimum oxidation state shown by all dhe elements ofthis series is 42
except Cr and Cu which show +1 oxidation state as wel, The number of oxidation
states shown increases from Se to Mn and then decreases till Zn which shows the +2
oxidation state only. AS a resul, among these elements, Cr and Mn show the

‘maximum number of oxidation states from +1 to +6 and +2 1047, respectively. From

Se to Ma, the highest oxidation state shown by any element is equal to the group
‘number but the later elements do not follow this trend. This is evident from the

following able

Temen T Iv [er [Ma [re [co [Ni Tor [2
CN E E E CS 00 CO jo io TT jr
number
Lowest 112 [+2 pa = fe fu fe
oxidation
state
tip Ja Ja [os [oe ja js ja ja ja ja
oxidation

It has been observed that the lower (+2, +, et.) oxidation states generally dominate
the chemistry ofthe fist transition series. Foran element he relative stability of
‘various oxidation stats can be explained on ie basis ofthe stability of? d and a?
configurations e. Ti ion (34s) is more stable than Ti (34s) because ofthe
presence of 34” subshell, Similarly, Mn?" (34) ion is more stable than Mn’“

(Gal's ion since Mo? ion has 3 subshel

It has also been observed

hat first transition series elements form ion oxides and
chlorides inthe lower oxidation states which are basic in nature. As the oxidation
state of the elements increases, covalent character and acidic nature of these
compounds also increases, 0.8, MnO (+2) is Basic, Mn;O, (+3) and MnO; (+4) are
amphoteric and MnO, (+7) is acidic, Similarly, CrO (+2) is basi, CO) (+3) is
amphoteric and CrO, (+6) i acidic, Also VC: (42) is basic and VOCI, (45) is acid.

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142 Complex Formation Tendency:

‘The elements ol fist tran

es Fulfil al conditions of complex formation and

are thus, most suitable for this purpose. As à result the cations of these elements
have a strong tendency o form complexes with certain molecules (eg. CO, NO, NH
tc) or several ions (eg. E CI, CN ete). These molecules and ions are called
ligands (L) and have one or more lone pais of electrons on their donor atom (usually
central atom) which they donate to the metal jonatom (M) during the process of
‘complex formation via ML coordinate covalent bonds. This happens because the
‘metal fons are electron deficient in most of their oxidation states or even the atoms

are elect

1 acceptors. Small size and high charge density of the metal ions facilitate
basicity ofthe ligands, The

‘complex formation tendency increases asthe positive oxidation state of the metal ion

the formation of the complexes which also depends on

‘The nature of the complexes depends onthe orbitals available on the metal ion / atom
for bonding. These orbital ares, p and d type. The structures commonly found in the

complexes of the el
tetrahedral and
bonding with
on is tetrahedral (detail ofthe complexes have been given ahead in this section).

mens of fist transition series are linear, square plana

ahedral. This shows thatthe metal orbitals are hybridized before

e ligand orbitals, e. [Ni(CN)s]” ion is square planar while (NICL*

1.4.3 Magnetic Behaviour:

“As has been mentioned cari

there are several Kinds of magnetism observed in the
ons ‘compounds or complexes of transition metals. Among the transition metal
compounds paramagnetism is common though some metals in the elemental form

also show ferromagnetism
Origin of Paramagnetism

‘The electrons being charged particles act as tiny magnets (or micro magnets) by

themselves and determine the magnetic properties ofthe substances in two ways:

(a Spin motion or spinning of the electron on its axis produces spin magnetic

moment and
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(6) Orbital motion or the movement of the electron round the mucleus produces

‘orbital magnetic moment

The resultant of the above two moments gives the total moment produced by an
electron. The observed magnetic moment of the compounds is the sum of the
‘moments of all the electrons present in them. I the two electrons with opposite spins
are pared in the same orbital, the magnetic moment produced by one electron is

cancelled by that caused by the other electron because both the electrons wi

have
equal but opposite moment thercby giving zero resultant magnetic moment. Such
substances which have paired electrons will not show paramagnetism, rather they are

diamagnetic.

Bur if here are unpaired electrons in the ionsatoms of the substance it has the
moment produced by all the unpaired electrons. The resultant or foal moment in
them is sufficiently high to overcome the magnetic moment induced by an
approaching magnetic field. Hence, such substances instead of experiencing

ulsion, ae attracted in a magnetic field and are called paramagnetic substances.

‘The magnetic moments of atoms, ions and molecules are expressed in units called

Bohr Magneton (B.M) which is defined in terms ofthe fundamental constants as

1BM.=

‘where = Planck's constan, e = electronic charge, € = velocity of light and m = mass

of electron,
‘The magnetic moment ofa single electron is given by the expression
is (BM) = g/5 ETT) (According to wave mechanics)

‘Where S= resultant spin quantum number and g = gyromagnetic ratio (called y

factor). The quantity STE Dis the value ofthe spin angular momentum ofthe

electron and thus g

the ratio of magnetic moment tothe angular momentum, For a

is nearly 2 Ge, 200023).

In transition metal compounds/complexes, the unpaired electrons are present in the

‘outer shell of metal ions and in such cases the spin component is much more

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significant than the orbital contribution because the orbital motion of these electrons
is said 10 be quenched or suppressed, Therefore, the latter can be neglected in
‘comparison to the former. In such case, the total magnetic moment is, therefore,

considered entire due tothe spin ofthe unpaired electrons and pi given by

SCH D = JASCCHT) BM (By puting the value of g=2)

[Now S= nxs where n= number of unpaired electrons and s= spin quantum number

Ciespectv of sen)
saisi
Ping his vale ofS inthe above expression

en [nS om,

ou FD BM.

His also expressed as pur, he. effective magnetic moment which is dependent only
où the numt

of unpaired electron and thei spins. Hence, this fr

n only formal

ula of magnetic

moment is also called

Thus, the permanent magnetic moment of 34:ransiion elements gives important
information about the number of unpaired electrons present in them and it varies with
2. The calculated magnetic moments corresponding to 1, 2, 3, 4 and 5 unpaired
73 BM, VE =283 BM, VS =

90 BM. and VHB = 5.92 BM. respective

électrons will be (using above formula) Y"

387 BM, VA

The number of unpaired electrons evaluated from the magnetic moment value for a
compoundieomplex gives the valuable information regarding the type of orbitals that
are occupied as well as those available for hybridisation and also the structure of the

ecules or complexes provided we have the idea of strength of the ligands

(speerochemical series). For example, here we discuss the structure of [MB

‘complexion in which Mn is in 42 oxidation state and ts coordination number is 4
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Mn atom (2=25): [Ar] 3484s? 4p?

Gears TPT) CH

Excited stat of M in

Ibridization st
of Mat? i

. SP Hybridization
In the complex ion, Mn? on is linked with four Br ions as ligands which exert weak

ligand feld on the metal fon orbitals As a result the five unpaired d-orbitals remain
‘unaffected and one s and 3p empty orbitals of metal ion (only four hybrid orbitals are
required) hybridise before bond formation producing sp’ hybrid orbitals thus giving
tetrahedral structure to the complex ion. The calculated magnetic moment of this
‘comps is neatly 5.92 BLM. which indicates the presence of five unpaired electrons.

IF hat is the situation, the tetrahedral structure of the complex ion is confirmed.

involving only and p orbital

‘Similarly for the complexes with coordination number 6, ie. six ligands ae attached

Lo the central metal on, we can pre

whether he complex is oute or inner orbital
‘complex from the knowledge of weak and strong ligands, eg. [Co(H:O))* is an
‘outer orbital complex and [Co(NHs) san inner orbital complex having the central

‘metal ion, Co" involving sp’ and asp" hybrid

respectively.
144 Formation of Coloured Tons/Compounds

The cause of the exhibition of colour by the ¡oncompoundsicompleres of the d

lock elements hasbeen discussed earlier, The elements of first transition series form

coloured ionsicompoundscomplexes due to the presence of unpaired electrons in

them. For example, [Co(H;0)0* is pink, Cu (Al) ion adits salts are colourless but

Ca’ (Aion and its compounds ae coloured, CuSO, 51,0 is blu which actually is
send as (CUH-OMISOLHLO and (CueNH is dark blue (almost ice
Similarly, [NIONO.)]* is red and [Ni(NH}* is Be. Among the other compounds

VOS is pale yellow, CrO is strongly yellow, MO is purple in colour, and
[T(H,0),)" i green coloured,
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The colour of the complex ion depends on the nature of he ligands and type of
complex formed. The metal ions with completely empty or completely filled de
GE), TAM,

subshell (as well as thei compounds) are colourless, viz. S
Cura), za

Elements of the first transition (4) series and thir compounds have been used in

y industrial processes. Their availabilty in a variety of oxidation states makes

them capable of forming intermediate products with various reactants and their
tendency to form inter

‘compounds which can absorb and activate the reacting
species facilitate their application as catalyst, For example, finely divided Ni is used
as a catalyst in hydrogenation reactions: MnO catalyse the decomposition of H:Os
TiCl is used as a catalyst for polymerisation of ethene in the manufacture of
polythene; V0 is employed in the eat
process of manufacture of H:SOs: Fe is used in the manufacture of NH, by Haber’s

process; Cu act as a catalyst inthe manufacture of (CH Si

i oxidation of SO; to SO, in the contact

13 during he synthesis.
of silicones. CuV is used in the large scale production of Nylon-66. Fell) ions

catalyse the reaction between iodide and peroxodisulphate ions

14.6 Formation of Intersti

and Non-stoichiometric Compounds

Elements of the 3d-an

on seres are capable of forming interstitial compounds,

82 TiC, V¿C, SeN, TIN, FaN ete. These compounds have the propenies of alloys

being hard and good conductors te

These elements also form non-stichiometric compounds. For example, titanium
forms TiO, (X=0.65 - 125 and 1.998 - 2000); vanadium forms VO, (x= 0.79 =
1.29): manganese forms Mn, (x= 0.848 - 1.00) ion form Fe,O (x = 0833 - 0.957),
ete. These compounds have variable composition and are formed due o the

variability of oxidation states and solid defects. Sometimes the imerstial and non

stoichiometric compounds ate the same.

1.4.7 Metallic Character and Alloy Formation

The metals of fist transition seres are hard, malleable and ductile, These exhibit face
centered cubic (fc), body centered cubic (be) or hexagonal close packed (hep) type
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of lice structures. These metals are good conductors of heat and elecuricity. Copper

and metals of the ion rad are softer than other metal

The common alloys ofthese metals areas follows: brass (Cu-Zn), nichrome (NiCr),
monel metal (Cu-Ni), german silver (Cu-Ni-Za), stainless steel (Fe-CeNiMo),

alnico steel (Fe-NI-CO-AI), ete. These alloys are harder and have high

melting
points than the parent metals. They are also more resistant to corrsion han their

148 Periodic Properties and Their Variation along the Series

The melting and boiling points, atomic and ionic rai, atomic volumes, ionization
energies and standard electrode potemials along wth reducing properties are the main
periodic properties of these metals along the series from Se 10 Za, which are
discussed below

a) Atomic Rad, Atomic Volumes and Tonic Radik

“As has been discussed ealir for block elements, th atomic radi of the element
of first transition series follow the same trend as is applied for other d-block
elements. The values generlly decrease along the series up to Ni then increase

slightly for Cu but pronounce

for Zu. Thus Zn has exceptional va

ve only lower
than those for he first two elements and higher than those of others. This is evident
rom the following table:

Meal [Se [Ti [V [@ [m [ke [Go [Ni [a [2
Romie Fa PEs ur for [06 fus [007 15
radi (pm)

‘This happens due to the increased attraction between the outer electrons and
increasing nuclear charge along the period. The close values of the atomic radi from

Cro Cu are due 10 the existence of increased screening effet of 3d-clecttons which
are added in each step and which shield the 4s-electrons from the inward pl though
the nuclear charge increases continuously in the series from one element tothe other.
“The screening effet in Za (Bd! is maximum and hence has ex

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The atomic volumes of these elements as given below are comparatively low because
ofthe filling of 3-orbitls instead of 4s which isthe subshell ofthe las shell. This
causes increased nuclear pull acting on the outer elctrons. The densities of these
elements are very high. Atomic volumes decrease up to Cu and increase thereafter for

Zo.
Metal atoms [Se vIG [m [Fe [Co [Ni [Cu [2
omic 1180 [110 [83 [72 173 [71 [67 [66 71 [92

volume (em)
‘The fone rad of these
radi of

ents follow the same tend as the atomic ad, te. the

ns with the same charge

nerlly go on decreasing as we move across

the series except only forth

last element. Rai of the bivalent and trivalent ons of

the elements of this series are listed below:

Bivalem [86 [TF IV [Ce [Ma

OC [00 fes fe fo [5 x Im | [m
om
O LA CC ES

la ner] [a jo | [a je je [= [=
(om

D). Melting and Boiting Points

‘The melting and boiling points of these elements are generally high and have

irregular tend in the values as given below

Blemenis [Se [TV [Gr [Ma [Re [Co [Ni TG [am

Melting | 1540 [1670 | 1900 | 175 | 1245 | 1555 [1495 | 1455 [1083 [420

pointe

[As is evident from hi table the highest melti point is for V (1900 °C) and Zn, the

last element has exceptionally low meling point (420 °C). Among other elements

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17. INORGANIC CHEMISTRY-I BSCCH-201
Ma and Cu have lower meling points as compared to other members. The boiling
points are very high, >2200°C excep for Zn (906°C) as expected.

+) Tonization Energies and Reactivity

‘The fist ionization energy values of 3drseries elements show imegular trend as

shown below
Elements: Se Ti VC Mn Fe Co Ni Cu Za

LE.(KD: 63 68 650 653 TIT 759 758 737 746
906

nd from Se 10

Bot the second and ihird LE. valves generally show be increasing

Za. The appreciably higher value of fist LE. for Za is tribut to the additional
subi associated with completly filed Sdsubsell (38%), The variation or
iregularty occuing in the vales of LE. across the series are mainly due o the
change in atomic rai because of he srening effect of xr icons added to 3d

subshell which is exerted on the nuclear charge.

On account of the factors given above, the elements of first transition series show less

reactivity

4) Standard Electrode Potentials and Redueing Properties

‘The standard reduction potentials of the elements of Ad-series except copper are

lower than tat of standard hydrogen electrode

Hlement [Se JR JV [Or [Mn [Fe [Co [Ni [Ga [2
Ey 1210 10 (oo ons [1.18 ou |. 025 108 |-076
(ols)

These elements evolve H; from acids though at very low rte. M + 2H" MP" à Hs
(). Cv does not react with acids, I has the tendency to get reduced. Sometimes the

‘metals are protected from the attack of acids by a thin impervious layer of an inert

oxide, e. Cr. These metals are oxidized easily to thet ons and hence are reducing

agent though poor due to the obvious reasons given above
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18. INORGANIC CHEMISTRY-IL BSCCH-201

1.5 THE BINARY COMPOUNDS OF FIRST TRANSITION
SERIES ELEMENTS

‘Those compounds which ae formed by the combination of two differ
fons are called binary compounds. For example, oxides, sulphides, halides,

‘hosphides, carbides, nitrides, et,

1.5.1 Oxides

‘The elements of the 3daransiion series reat with 0

gen a igh temperature 0 give
oxides. These oxides are less basic and less soluble in water. Oxides in lower
‘oxidation states are ion and basic, nthe intermediate oxidation states their nature is
amphoteric and in higher oxidation states, ionic nature decreases and covalent nature

increases thereby increasing the acidic character ofthe oxides, I means the aci

yor

salt depends on its covalent nature which in tum is based on the oxidation state of
the element. Thus, oxidation state «covalent nature & acidic nature. Accordingly the
oxides may he classified as (a) basic oxides, (b) amphoteric oxides and () acidic

oxides

(a) Basie oxides are those which are formed by the metals in the lower oxidation
states, These are ionic in nature, soluble in non-oxidisng acids, eg. HCI. For
example, TO, CrO, MnO, FeO, €u:0. CoO, NiO, et.

(0) Amphoterie oxides are the oxides containing the metals in the intermediate
‘oxidation states. These oxides are also soluble in non-oxidisng acid, e.g, HCL
Examples TIO». VO, COs, MniO4. MnOs, CuO, 240, ee

(©) Acidie oxides are of weak acidic nature and are formed by the elements in higher
‘oxidation states. These are soluble in bases. For example, V¿0S, COs, MnO,
MoO ete

Reducing

determines the redox nature of oxides. The oxide containing the metal is lower

oxidising mature of oxides. The electron exchange property

oxidation state act as electron donor and hence is a reductant (reducing agent). As
atomic number increases, the reducing property in the lower oxidation state also
increases, e 2, TIO < VO < CIO. If the meu

in the oxide isin higher oxidation state

the oxide is electron accept or oxidising agent, e... C1Os, MnzO: ee

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19. INORGANIC CHEMISTRY-IL BSCCH-201

1.5.2 Halides

The elements of 3d-ransiion series react with halogens a high temperature o give
halides, The reactivity of halogens goes on decreasing from F to I. Fluorides are
nic, others have ionic as well as covalent nature. Hades are formed by many of
these elements in diferent oxidation sates, eg. TICH „TICLVCH,VClsete

1.5.3 Sulphides

Metal sulphides may ether be prepared by direct heating the mixture of metal and

sulphur or by treating metal at solution with HS or Nas
Metal +5 =, metal sulphide

(Oc mca salt soltion + HS — metal sulphide

‘Metals in low oxidation state form sulphides which are insoluble in water.

154 Carbides

Metal carbides are generally prepared by te following two methods:

Meal + carbon 2%» metal carbide

Or metal oxide + carbon > metal carbide

The carbides ofthese metals ae classified as follows:

(a) Metallic or Interstitial carbides

“These carbides are prepared a i
vec—vc

TO +20 — TIC + CO

Ber — Fac

These are hard solid, have meulie properties like lustre, are stable at high

temperature, chemically inert and are conductors. Ni does not form carbide. In solid

state, these have

‚hedrl or octahedral voids which are occupied by carbon atoms.

(0) Saltike carbides

‘These carbides ar limited to Se, Cu and Zn only and are ion in mature

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20. INORGANIC CHEMISTRY-IL BSCCH-201

Se0y 470 —+ 28eC:+3C0
SC: +20 — Call: + SOM):
Za CH — Za: 4 Hy

Zoey +20 —+ Cay + 20H

1.6 RELATIVE STABILITY OF OXIDATION STATES OF
THE ELEMENTS OF FIRST TRANSITION SERIES

‘The stability of an element is determined by its electronic configuration, The
elements ofthe Adarandtion series, generally exhibit variable oxidation states and are
eg. Ti > Ti and Fel" > Fe et

states are less stable than the higher oxidation states, This

stable in a particular oxidation state

Generally, lower oxid

relative stability depends on many factors

(a) Fille, alfil and vacantd-orbitals present inthe compound, ie. °° and &?
er configurations, eg. TH) > THC
4. Cu 4) is less stable

configurations are more stable than o

Maia") > Mn”), However its not always tue,

than Cu (64°) due to high lice energy and solvation energies of Cu°* in solid
state and in solution,
(©) Higher oxidation states become less stale as atomic number increases. For

> VE eee NE > CH",

example, Se” >
(© Inthe binary compounds of elements of 3 transition series, it has been observed
that halogens and oxygen also illustrate the tend in stability. Generally, the
group oxidation state for many elements is brought out more readily by oxygen
than fluorine, the strongest halogen. This may be because fewer oxygen atoms are
required than fluorine atoms to achieve the same oxidation state, For example,
the group oxidation state (+7) of Mn is achieved in MAS”, but Mi
been prepared. Inthe dblock element, the oxidation states can be stabilised by

+ has ne

complex formation. Low oxidation states are less stable and ligands like CN. Ns
NO, CO, CMa Calla ete. called acceptors form complexes in these low
‘oxidation states 10 stabilise them. These complexes are known as x-complexes,
eg. INICOM). [CHCAL):), [FCH
stabilized by complex formation with highly electronegative ligands,

ete, Higher oxidation states are

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21. INORGANIC CHEMISTRY-IL BSCCH-201

(4) The compounds in any oxidation state of the metal are regarded as sable if hey
have fre existence, are not oxidised by air, are not hydrolysed by water vapour
‘do not disproportionate or decompose at normal temperature.

1.7 THE COMPLEXES OF THE FIRST TRANSITION
SERIES ELEMENTS, THEIR COORDINATION
NUMBER AND GEOMETRY

‘The elements of fis transition (34) series Fulfil all conditions of complex formation
and thus are most suitable for this purpose. The general representation for the

complexes is as follows

[M+— LL" where n represents the number of lone pais accepted by the central
‘metal atonvion from the ligands (L) and xis the charge on the metal complex which
may be positive or negative or even zero in neural complexes. All the elements of
¡bis series form complexes with a variety of ligands, eg. [CIO
0

[Ag(NHo)]" tc. The elements of this series form stable complexes with N,

ls
HEN, INNE, (COOP. [Co(NH)XSCN),_(CuCNH
©, and

halogen donor ligands
‘Coordination Number (CN)

‘The number of ligands

sonodemate onl) di

iy atached tothe central metal atom

/ on oF more appropriate

the number of lone pars of electrons accepted by the
central metal tom / ion from the ligands (mono as wel as polydentate) in the process

or ions), is known asthe coordination

of the formation of the complexes (molec
‘number (CN. ofthe metal. Inthe above examples, the CIN. of Ag" ion is 2, that of
Cu" ion is 4 for Ce", Ni, Col, Co and Fe” ions it is 6, The central metal atom

fon and attached ligands are kept within the square brackets called coordination
sphere. With the polydentate ligands the metal atom / ios form ring type complexes

‘known as chelates (meaning claw).
Geometry of the Complexes

‘The coordination numberof the central metal stonvion ofthe complex is intimately
‘elated with its geometry. The relationship may be shown a follows:
© Geometry of the complex

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22. INORGANIC CHEMISTRY-IL BSCCH-201

Linear: Cu’ and Ag’ complexes, e.g. [AgNHy]

4 ‘Teuahedral: Mn, Co", Fe", Ni", Cu" complexes with weak
ligands vic. HO, CI, Br, Fete, eg. [MACL]”, [MB
[NICK], [CUCL IFeCL ete

Square planar: Ni", Cu” complexes with strong

iz. CN, NH, etc, eg. [Nildmg):}, (Cute)
CENTRES
6 Octahedral: CP", Ce”, Mn, Fe, FOCO”, Co”, Ni

complexes with weak and. stor
ICKMO)]", EMoH OV", [NINA [CANINA
[Coen] e

Field ligands, ez.

I

ay be recalled that octahedral complexes of the metal ions with weak field
ligands are outer orbital (also called high spin) complexes involving sp

hnybridisation and those with strong field ligands ae inner orbital (also known as low

spin) complexes, the central fon undergoing dsp" hybridisation

1.8 SUMMARY

In contrast to main group elements, the last eleeton in the atoms of d-block elements
centers the (n-1)d-subshe which influences the characteristics and periodicity in

properties of transition elements. Hence,

€ text material ofthis nits related with
characteristic properties in general of d-block elements such as their electronic

configuration, variable oxidation states, complex formation tendency, magnetic

properties, formation of coloured ions / compounds, cata
intersisl and non-stoichiometric compounds, alloy formation, metallic
‘melting and boiling points, atomic and ionic radi, ionization energies, reactivity.

activity, formation of

Saracen,

standard electrode (rection) potential and reducing properties, The above properties
have also been discussed for the elements of the first transition (34) series in brief

giving examples where ever possi

e. A brief but concrete account of binary

compounds of elements of 3d-series along wit relative stability oftheir oxidation

states, their complexes, coordination num

and geometry of the complexes has also

been given

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23. INORGANIC CHEMISTRY-IL BSCCH-201

1.9 TERMINAL QUESTIONS
1. Ge a br

F note on the factor responsible Tor anomalous el

configuration of Crand Cu.

hat accounts forthe complex formation tendency of d-block elements?

Write a short note on the paramagnetism shown by deblock elements
Why do 3d-series elements form coloured ions and compounds?
What are the non-stoichiometic compounds?

What ar alloys? Gi

sy two examples.

Mn and Cr have highest number of oxidation states among fis transi

n (3d)

series elements”. Comment
8. Which one is more stable: Ti“ of Ti?
9. as for a metal ion with 3 unpaired electrons is
a) LT3BM
b) 283 BM,
©) 387 BM.
à 490BM,
10, Finely divided Ni is used in
a) The manufacture of H5$0,
D) The manufacture of HNOs
9) The manufacture of NH
d The hydrogenation

11, Bras isan
a) Cuzn
b) Cure
9 CEN
d Mae

12. MnO is

2) An acidic oxide
D) An amphoteric oxide
©) A basi oxide

©) None ofthe above

1.10 ANSWERS

110 7: please refer tothe text

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24. INORGANIC CHEMISTR'

an BSCCH-201
8. Ti" (Gd?) is mor sable than Té 54!)

9.

10.4

Ha 12.b

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