Transition Elements (B.sc-Ii) Inorganic Chemistry Paper-I
Transition Elements (B.sc-Ii) Inorganic Chemistry Paper-I
Transition Elements (B.sc-Ii) Inorganic Chemistry Paper-I
Transition Elements
The elements lying between s and p-block of periodic table that constitute a large
block of elements are called transition elements. These elements have partly field
(n-1)d orbital. Since last electron fill into d-orbital, so they are called transition
elements or d-block elements. They show transitional behavior.
These d-block elements are placed into four series of ten elements in each, which
are kept in 4th period (3d series); 5th period (4d series) 6th period (5d series) and 7th
period (6d series incomplete series).
(i) All transition metals are hard except for group 11 (copper family) and have
high melting and boiling point. Nearly ten transition elements have melting point
above 2000˚C and three elements Ta, W and Re have melting points above
3000˚C.(ii) They are hard, strong refractory and electropositive.(iii) The transition
elements all have high densities. Os and Ir have densities of the order of 23g/cm 3.
(iv) Most of the transition elements are malleable and ductile.(v) Most of the
transition metals are good electrical conductors.(vi) Most of elements form
coloured compounds of every colour of the rainbow.(vii) They form alloy with
other metals.(viii) These elements form well known coordination complexes.(ix)
Transition metals exhibit several oxidation states.(x) Most of the transition metals
and compounds are used as catalyst.
The general properties of d-block elements of all the series (3d, 4d, 5d ,6d are
not so different because of their electronic configuration. Which includes the
number of electrons in d-orbital are generally same only vary in number in s-
orbital it is invariably 0, 1 or 2. important physical properties of the elements are
discussed below and the data are given in table -A.
Property/ SC TI V Cr Mn Fe Co Ni Cu Zn
Element
Atomic 21 22 23 24 25 26 27 28 29 30
number
Outer 3d1 4s2 3d24s2 3d3 4s2 3d4 4s2 3d5 4s2 3d6 4s2 3d7 4s2 3d8 4s2 3d10 4s1 3d104s2
electronic
configura
tion
Atomic 1.60 1.46 1.1.31 1.25 1.29 1.26 1.25 1.25 1.28 1.33
size (A0)
Ionic 0.90 0.88 0.84 0.80 0.76 0.74 0.72 0.69 0.79
radius (
(A0)M2+
M3+
Stable +3 +4 +3, +4, +2, +3 +2, +3, +2, +3, +2, +3 +1, +2 +1 +2 +2
oxidation +5 +6 +6,+7 +7
state
Red.Pot.E0 -
-1.63 -1.20 -0.91 -1.18 -0.44 -0.28 -0.25 +0.34 -0.76
M2+/M (V)
Density 3.1 4.5 6.1 7.2 7.6 7.9 8.7 8.9 8.9 7.1
(gm/ml)
Melting 1539 1725 1900 1875 1245 1536 1495 1453 1083 420
Point (0C)
Boiling 2730 3260 3450 2665 2150 3000 2900 2730 2595 906
Point (0C)
IstIonizati 632 659 650 652 717 762 758 736 746 906
on
Energy/m
ol)
Electrone 1.3 1.5 1.05 1.6 1.05 1.8 1.8 1.8 1.8 1.6
gativity
Heat of 15.9 15.5 17.6 13.8 14.6 15.3 15.2 17.6 13.0 7.4
Fusion (Kj
/mol)
Heat of 338.8 405.4 443.5 305.3 224.6 333.7 389.7 380.7 338.9 114.6
vaporizati
on
Crystal Fcc Hcp Bcc Bcc Bcc Bcc fcc hcp Fcc hcp
structure
Properties
1, Electronic configuration of Transition Series Elements:
Here, [Ar] means electronic distribution of atomic no. 18. The general electronic
Here, [Xe] means electronic distribution of atomic no. 54. The general electronic
configuration of the 5d series elements may be given as (n-1)d1-10 ns1-2; n=6
2.Melting and Boiling points: The d-block elements have very high melting and
boiling points and melts above 900 c. Due to completely filled d-orbital elements
like Zn, Cd, and Hg do not form covalent compound. The formation of covalent
bond present in rest elements as it also accounts of the having incomplete d-
orbital.
These points may be noted from the data of table. (i) As it is clear from the table-
A that the atomic and ionic radii show a gradual decrease in their values in any
period. This is due to increase in nuclear charges try to pull the electron clouds
toward itself that is attraction of electrons towards nucleus increases. This
increase in attraction leads to decrease in radii values across each period. There
are however few exceptions, the atomic radii of the elements from chromium to
copper are very close to one another. This is explained as further the addition of
extra electrons screen the outer electron very effectively from the nuclear charge
thus screening effect increase considerably due to increase in atomic number and
hence there is a marginable increase in effective nuclear charge .Thus results a
small change in atomic radii of the middle elements in any period .
(ii) In any particular series, the atomic radius attains the minimum value for
elements of 8th group (that is 8,9 and 10) and increases again towards the end of
the series. This is explained in terms of increase force of repulsion among the
added electrons which dominate to the attractive forces due to increased nuclear
charge and results in expansion of electron cloud.
(iii) On descending in the group, principal quantum number ‘n’ increases and
atomic size is therefore is expected to increase from top to bottom but the
increase are not same for all the members. The difference in radius of second and
third series elements is very small as compared to first and second series
members. This is due to lanthanide contraction here the inclusion of 14
lanthanide elements between La and Hf.
4. Density: The transition elements show a high density compared to alkali and
alkaline earth metals. Due to smaller size and increased nuclear charge and poor
screening effect by the orbitals the electron are attached more strongly towards
the nucleus this results a decrease in atomic volume of transition metals and
there is an increase in density .It can be also seen a trend of table that densities
increases from period 4 to 6 elements the osmium and iridium with highest values
(23g/cm3) and then decreases in a group there is also an increase in density of
elements. Thus, increase in densities is due to small radii and closed packed
structure of the elements .The densities of the second series is nearly two times
those of the second series elements due to the atomic masses because twice
those of the first series elements .
6. Oxidation states
This is one of the peculiar properties of transition element that the element
exists in different stable oxidation state. Change in oxidation state usually shown
a unit change of Fe3+ and Fe2+ as compared to non–metals usually changed by two
units. After calcium (atomic no. 20 the electronic configuration 1s2, 2s2, 2p6, 3s2,
3p6, 4s2) the next ten elements will have the electronic configuration started with
filling of 3d orbital from one to ten. This prevails exception in the case of Cr and
Cu, due to extra stability of their half filed or completely filled configuration, these
two electrons prefer to shift their one 4s electron to 3d orbital. Therefore, the
first element of 1st transition series have an oxidation number (+II) when two 4s
electron are engaged in bonding and (+III) when addition of one 3d electron is
involved in bonding .Thus, from titanium to chromium a regular change in
oxidation state takes place with a correlation between electronic structure and
minimum and maximum oxidation states. Further the highest oxidation state of
these elements, all of the s and d electrons are used in bonding. After the 3d5
configuration the tendency to show higher oxidation state decreases among the
rest elements. Fe has a maximum (+VI) oxidation state and ruthenium and
rhodium the often two elements of their group contain oxidation state (+VIII) due
to their larger size. The oxidation states of these elements are shown in Table 1.6
Element SC TI V Cr Mn Fe Co Ni Cu Zn
Electronic 3d14s2 3d24s2 3d3 4s2 3d54s1 3d54s2 3d64s2 3d74s2 3d84s2 3d104s1 3d104s2
structure
Oxidationstate II II I I
III III II II II II II II II II
IV IIV IV IV IV IV
V V V V V V
VI VI VI
The unit of magnetic moment expressed is called Bohr magneton (BM). For
an electron it is given by:
µB = eh/4πmc
µs = √4S+1
Where, S=total spin quantum number of unpaired electrons.
µs = = √4x1/2 + 1 = √3 = 1.73 BM
Magnetic moment for an atom or ion or molecules containing more than one
unpaired electron (n) can be calculated as:
µs = √n(n+2)
The observed and calculated values of magnetic moments for first transition
series elements are given in the following table 1.7
Metal ions which contain completely filled d- orbital like m2+, Hg2+, Cu + etc are
normally white for example ZnCl2 is white.
The transition elements have unique property to form complex salts due to
presence of vacant d-orbital to accept electron from Lewis bases, groups which
are capable to donate a pair of electrons. These groups are called ligands. The
number of ligands coordinated to metal is called the coordination number of
metal ion. The ligand may be neutral groups as NH3 and ion as Cl- or CN- etc.
(Fe(CN)6)4-and (Fe(CN)6)3-complex compounds are formed by donation of six pairs
of electrons from CN- to Fe2+ and Fe+3 respectively .
[Ni(CN)4]2-and [Ni(Cl)4)2- complex compounds are formed by the gain of four pairs
of electrons from CN- and Cl- ions. Various other transition metals also form
complex compounds with N,O,F and S atoms as donor .
11. Reactivity: The reactivity towards other groups is found less for the transition
metal’s high ionization potential and smaller size. Thus, they have tendency to
remain un reactive. Elements like platinum and gold do not react with air and are
called noble metals.
The oxides are basic in the low oxidation state and basic in high oxidation state of
the metal involved. Therefore, basicity decreases from left to right in the first
series of elements. Amphoteric oxides are formed by the intermediate oxidation
state of metal the basic and amphoteric oxides when dissolved in acid forming
hexaaquo complex ions [(M(H2O]6n+.
MO type oxides in which each M2+ metal ions and each O2- ion is surrounded by
six M2+ ion have a NaCl type crystal structure.
2CrO3+H2O= H2CrO7.
It is a strong oxidizing agent and oxidizes many organic compounds the acid base
character of the first transition series oxides in different oxidation state are given
in the following table.
Hydrides: Almost all the hydrides of first transition series forms hydrides by the
accumulation of hydrogen atoms in their interstitial space. Such hydrides are
called interstitial hydrides and show variable composition e.g. TiH1.8
, PdH0.6 and NbH0.7 etc. The M-H bond cannot categorise as ionic o covalent. These
are solid metal like appearance, brittle with magnetic and conducting properties.
Carbides: The metals interact with carbon at high temperature forming carbides.
Apart from carbon, atom like boron and nitrogen can occupy empty spaces
between the atoms of these metals. Such compounds are called interstitial
compounds and called as carbides, borides and nitrides respectively. The carbon
atoms cause a distortion in space of metals like Cr, Mn, Fe, Co and Ni due to less
space in crystal lattice to occupy. This is the reason that is why they are
highly reactive. These interstitial compounds are high melting and hard. These are
used for making heat resistant material and cutting tools as well as kiln and gas
turbine and jet engines.
+1 +2 +3 +4 +5 +6 +7
Zn ZnO
(ii)Transition metal in high oxidation state form stable complexes with the small
highly electronegative and basic ligands like F-, Cl-, NH3, IO65-, TeO66-, etc. While
these metal in low oxidation state (e.g. +1, 0, -1) give stable complexes with pi
acid ligand like CO, CN-, PCl3, C6H6 etc. The complex compound formed by
transition metal atoms in low oxidation states contain L M coordination
bond.
(iii) When transition metal form complexes with same ligand in different oxidation
states, the complex compound having the metal in higher oxidation state is more
stable e,g, [Co3+(NH 3)6] 3+ is more stable than [Co2+(NH 3)6] 2 . Greater
stability is due to the fact the metal cations having higher charge has greater power
to attract the lone pair of electron on the ligand. In other words we can say that
since the metal cation with high charge is smaller in size, it can attract the lone pair
of electrons of the ligend more strongly and hance can give more stable complex
ion.
Thus, the coordination number is the number of ligands which surround the
metal in a specific arrangement in space this specific arrangement of ligands
around metal ion adopt a definite shape to have a minimum electrostatic
repulsion and maximum stability. This definite shape is termed as geometry of
complex compound. For example, in the compound [Co(NH3)6] Cl2, metal ion Co2+
is surrounded by six ammonia molecules, formed the coordination compound and
of coordination number six and octahedral geometry. Metals Cu, Ag and Au form
complexes with coordination two and adopt a linear geometry. The examples of
such coordination compounds are [CuCl2],[Ag(NH3)2]+ ,[Ag(CN)2]- and [Au(CN)2]-.
In such cases all the complexes are linear and involved completely filled d-
orbital(d10) metal atom. Complexes with coordination number three are not very
common. Examples are:[Hg I3]- ,adopt a planar geometry having coordination
three. Other complexes which show coordination three are K2[(CN)3].H2O,Sc[N(Si
Me3)2]3
Complex compound with coordination number four can isolated for number of
metals, these are usually adopted tetrahedral and square planar geometry .
Although both the complexes have same coordination number four, but adopt
different geometry because of steric and electronic factor. A tetrahedral
geometry is more favoured due to steric effect makes maximum distance
between ligands and minimum repulsion. This can be also explained on the basis
of strength of ligand and formation of hybrid orbitals of central metal atoms , Ni
involves 4s and 4p orbital in Ni(Cl4)4 whereas 3d and 4s in [Ni(CN)4]2- complexes
adopt a tetrahedral and square planar geometry respectively Other complexes of
square planar geometry are [Cu(NH4)]2+ and [Ni(Py)4] ;Py=pyridine , [Ni(NH)4]2+ etc.
[Mn(CN)6 ]3-, and [ Sc(F)6 ]3- etc. The geometry of various complexes in several CN
numbers are shown below.
For example-
(iii) CN=3 geometry planar and pyramidal, example- K2[Cu(CN)3]H2O and HgI3-
(iv) CN=4 geometry square planar and tetrahedral, given in above figure 1.0
example- Ni(CN)42- and NiCl42- and NiBr42-
(v) CN=5 trigonal bipyramidal and square pyramidal, example- [CuCl5]3-, Fe(CO)5
and Ni(Et3P)2Br3
(vi) CN=6 octahedral geometry given in above figure 1.1 example- K4[Fe(CN)6],
[Co(NH3)6]3+
(vii) CN=7 pentagonal bipyramidal, capped octahedron and capped trigonal prism,
example- [Zr(F)7]3-, [MoF7]- [M(F)7]2-, M=Nb or Ta
Exercise-
Long Answer Type Questions:
3d-series:
(a) Electronic Configuration (b) Atomic and Ionic radii (c) Ionization Potential
(d) Variable
valency (e) Magnetic behaviour and (f) Complex formation (BHU (Hons) 1986)
(a) Electronic configuration (b) Magnetic properties (c) colour (d) complex
formation (Lucknow 1988)
4. What are transition elements? Discuss the characteristics in which they differ
from non- transition elements. Is Zinc a member of the first transition series?
(Lucknow 1990)
5. The elements of second and third transition series resemble each other more
closely they resemble the elements of first transition series. Explain this fact with
reference to their atomic radii, oxidation states, magnetic behaviour and complex
formation tendency. (VBSPU Jaunpur, 2006)
6. What are transition elements? How are they classified? Discuss the electronic
configuration and tendency to form complexes in different oxidation states of the
elements of transition series. (VBSPU Jaunpur, 2007).
(a) Oxidation state (b) Colour (c) Magnetic properties. (MGKV Varanasi 2009)
8. What are d-block elements? How do d-block elements differ from f-block
elements? Comment on their (a)size (b) oxidation state (c) Magnetic properties.
(MGKV Varanasi 2010)
(a) size (b) colour of salt (c) magnetic properties (d) complex formation
properties. (MGKV Varanasi 2012)
10. What are transition elements. Discuss the electronic configuration and colour
of the first Transition series. (MGKV Varanasi 2014)
11. Discuss binary compounds of first transition series elements with respect to
oxides and carbides.
12. Discuss binary compounds of first transition series elements with respect to
oxides and hydrides.
13. Discuss binary compounds of first transition series elements with following
respect: (i) oxides (ii) hydride (iii) carbide
14. Discuss binary compounds of first transition series elements with following
respect:
15. Discuss the coordination number and geometry found in 3d series transition
elements.
1. Why the common oxidation of the first transition series elements increases up
to manganese and then decreases?
2. Why Ti3+ complex compounds are coloured but Ti4+ complex compounds are
colourless?
3. Cu2+ complexes are coloured but Zn2+ complexes are colourless. Give reason.
7. Give with reason the more common oxidation state shown by first transition
series (3d) Elements. (Kanpur 2008)
8. Find the Number of unpaired electrons in Mn4+ and Cr3+. (Kanpur 2011)
10. Transition elements show variable valency state. Why? (Agra 2009)
11. Transition metal ions act as Lewis acids. Explain. (VBSPU Jaunpur)
13. Why Mn(II) show maximum paramagnetic character among the bivalent ions
of first Transition series. (Garhwal 2011)
15. Write the following oxide with their increasing order of acidity, VO, VO 2, V2O5
and V2O3. (Garhwal 2011)
(a) (n-1) d10ns0 (b) (n-1) d1-10ns1-2 (c) (n-1) d1-10ns0 (d) (n-1) d0-10 ns2
(a) Cu and Ni (b) Cu, Ni and Zn (c) Cu, Ni and Cr (d) Ni and Cr
11. What is the coordination number of Nickel and shape of complex in [Ni(CN) 4]2-
.
12. What is the coordination number of Nickel and shape of complex in [NiCl4]2-.
13. What is the coordination number of Iron and shape of complex in K4[Fe(CN)6].
(a) 6 and pentagonal (b) 4 and tetrahedral (c) 4 and square planar (d) 6 and
octahedral14. What is the coordination number of Rhenium and shape of
complex in [ReH9]- ?.
Answers 1- (a), 2-(b), 3-(c), 4-(d), 5-(a), 6-(c), 7-(a), 8-(c), 9-(d), 10-(a), 11-(a), 12-
(c), 13-(d), 14-(a), 15-(b)