Sunday, October 21, 2007

Study Guide Ch.16.Transition Elements

See the practice questions on this chapter in

JEE Syllabus

Transition elements (3d series):
Definition, general characteristics, oxidation states and their stabilities, colour (excluding the details of electronic transitions) and calculation of spin-only magnetic moment;

Coordination compounds: nomenclature of mononuclear coordination compounds, cis-trans and ionisation isomerisms, hybridization and geometries of mononuclear coordination compounds (linear, tetrahedral, square planar and octahedral).

Preparation and properties of the following compounds: Oxides and chlorides of tin and lead; Oxides, chlorides and sulphates of Fe2+, Cu2+ and Zn2+; Potassium permanganate, potassium dichromate, silver oxide, silver nitrate, silver thiosulphate.

Main topics in the TMH Book
The material in Jauhar's book of XII is very detailed and is very good to understand the syllabus of the topic. I am not trying to give a detailed treatment in my study guides. These are only some issues that I like to highlight. Reading of a text is essential to understand the topic. And then answering the comprehensive list of questions provided by JEE books like TMH. I am trying to record the material in the way that I am feeling it easy to understand.

A transition element may be defined as an element which in its elementary form or in at least one of its oxidation states, possesses partially filled d orbitals in its penultimate shell.

The definition excludes zinc, cadmium, and mercury from the transition elements, however their properties are an extension of the properties of transition elements, they are generally considered along with transition elements.

Three series of elements are formed by filling the 3d, 4d, and 5d shells by electrons.

First series or 3d series: Scandium to Zinc
Second series or 4d series: Yitrium to cadmium
Third series or 5d series: Lanthanum to hafnium to mercury

In JEE syllabus only 3d series is there.

Transition Metals
The ten elements from Scandium to Zinc form the first transition metal series. They closely resemble each other and are hard, dense, shiny metals with high melting and boiling points. They readily form alloys and have other properties in common. Crossing the period from Sc to Zn there is a small decrease in atomic radius and increase in electronegativity and ionisation energy. Most of the properties of transition metals are related to their electronic structures.

Electronic Structure
Transition elements are characterised by having a partially filled d sub-shell

Sc [Ar] 3d1 4s2

Ti [Ar] 3d2 4s2

V [Ar] 3d3 4s2

*Cr [Ar] 3d5 4s1

Mn [Ar] 3d5 4s2

Fe [Ar] 3d6 4s2

Co [Ar] 3d7 4s2

Ni [Ar] 3d8 4s2

*Cu [Ar] 3d10 4s1

Zn [Ar] 3d10 4s2

*Note that in Cr the arrangement [Ar] 3d5 4s1 with half-filled 3d and 4s sub-shells is more stable than [Ar] 3d4 4s2.

In Cu [Ar] 3d10 4s1 with a completely filled 3d sub-shell and a half-filled 4s sub-shell is more stable than [Ar] 3d9 4s2.

General characteristics

1. They are hard and brittle metals.
2. They have a high melting and boiling points and have higher heats of vaporization than non transition elements.
3. The transition elements have very high densities as compared to the metals of groups I and II (s-block).
4. The first ionization energies of d-block elements are higher than those of s-block elements but are less than those of p-block elements.
5. They are electropositive in nature.
6. Most of them form coloured compounds.
7. The have good tendency to form complexes.
8. They exhibit several oxidation states.
9. Their compounds are generally paramagnetic n nature.
10. They form alloys with other metals.
11. They form interstitial compound with elements such as hydrogen, boron, carbon, nitrogen etc.
12. Most of the transition metals such Mn, Ni, Co, Cr, V, Pt etc. and their compounds have been used as good catalysts.

Each of these characteristics is explained in detail in Jauhar's XII CBSE book in Unit 9.

Oxidation States
Transition metals form ions which are characterised by having a partially filled d sub-shell. In case of 3d series electrons in 4s as well as electrons in 3d participte in reactions. Lower oxidation states represent the participation of electrons in 4s only. Higher oxidation states result when electrons in 3d also participate.
The common oxidation states of various elements are:

Sc 3
Ti 2 3
V 2 3 4 5
Cr (1) 2 3 (5) 6
Mn 2 3 4 (5) 6 7
Fe 2 3 (4) (5) (6)
Co 2 3 (4)
Ni 2 3
Cu 1 2
Zn 2

Oxidation states in brackets are unstable

Sc and Zn are not typical transition metals as they only have one oxidation state which does not have a partially filled d sub-shell. (Sc3+ [Ar], Zn2+ [Ar] 3d10).

Common oxidation states are +2 and +3, with the +2 state more common towards the end. The higher oxidation states are shown in compounds with electronegative elements like O, Cl or F (e.g. Cr2O7^2- [+6], MnO4^- [+7]).

Variable oxidation state is found because of the small difference in energy between the 3d and 4s sub-shells. This allows varying numbers of electrons to be used in bonding. When forming ions transition metals lose electrons from the 4s sub-shell before the 3d.

e.g. Fe2+ [Ar] 3d5 (NOT [Ar] 3d4 4s2)

Ni3+ [Ar] 3d7

Cr3+ [Ar] 3d3

Mn2+ [Ar] 3d5

Catalytic Action
The ability of transition metals to exist in various oxidation states makes them important industrial and biological catalysts.

Used in Contact process for the manufacture of sulphuric acid.

2SO2 + O2 2SO3

Fe or Fe2O3
Used in Haber Process for manufacturing ammonia

N2 + 3H2 2NH3

Used in Manufacture of nitric acid from ammonia.

4NH3 + 5O2 4NO + 6H2O

then NO NO2 HNO3

Used in Hydrogenation of alkenes

CnH2n + H2 CnH2n+2

Coloured Solutions
Most transition metal compounds are coloured.

Sc - scandium salts, such as the chloride, ScCl3, are colourless and are not typical of transition metals

Ti - titanium(III) chloride, TiCl3, is purple

V - vanadium(III) chloride, VCl3, is green

Cr - chromium(III) sulphate, Cr2(SO4)3, is dark green (chromate(VI) salts are yellow, dichromate(VI) salts are orange)

Mn - manganese compound - potassium manganate(VII), KMnO4, is purple (manganese(II) salts eg MnCl2 are pale pink)

Fe - iron(III) chloride, FeCl3, is yellow-orange-brown.
Iron(II) compounds are usually light green and iron(III) compounds orange/brown.

Co - cobalt sulphate, CoSO4, is pinkish

Ni - nickel chloride, NiCl2, is green

Cu - copper(II) sulphate, CuSO4, is blue.

Most common copper compounds are blue in their crystals or solution and sometimes green.

The blue aqueous copper ion, Cu2+(aq), actually has a more complicated structure:
*[Cu(H2O)6]2+(aq) and when excess ammonia solution is added,
after the initial gelatinous blue copper(II) hydroxide precipitate is formed, Cu(OH)2
it dissolves to form the deep royal blue ion: *[Cu(H2O)2(NH3)4]2+(aq).

Copper(II) oxide, CuO, black insoluble solid, readily dissolving in acids to give soluble blue salts e.g.
copper(II) sulphate, CuSO4, from dilute sulphuric acid,
copper(II) nitrate, Cu(NO3)2, from dilute nitric acid
and greeny-blue copper(II) chloride, CuCl2, from dilute hydrochloric acid.
Copper(II) hydroxide, Cu(OH)2, blue gelatinous precipitate formed when alkali added to copper salt solutions.
Copper(II) carbonate, CuCO3, is turquoise-green insoluble solid, readily dissolving in acids, evolving carbon dioxide, to give soluble blue salts (see above)
Copper's valency or combining power is usually two e.g. compounds containing the Cu2+ ion. However there are copper(I) compounds where the valency is one. This variable valency, hence compounds of the same elements, but with different formulae, is typical of transition metal compounds e.g.
copper(I) oxide, Cu2O, an insoluble red-brown solid,
or copper(I) sulphate, Cu2SO4, a white solid.

Zn - zinc salts such as zinc sulphate, ZnSO4, are usually colourless and are not typical of transition metals.


In an isolated atom or ion the 3d orbitals have the same energy (degenerate). In a complex ion the d orbitals are split due to different overlapping with ligands.
Transitions between the two levels will absorb energy of frequency n where DE = hn. For the transition metals this occurs in the visible part of the spectrum, making the ion coloured.The colour of the ion is complementary to the colour absorbed. i.e. yellow/ green absorbed -ion appears blue/ violet. The colour of the ion depends mainly on the transition metal but can be affected by different ligands.

The Typical Characteristics of Transition Metals

(a) Some General Physical Characteristics

Generally speaking they are hard, tough and strong (compared with the Group 1 Alkali metals!) because of the strong metallic atom-atom bonding.

Good conductors of heat and electricity (there have many free electrons per atom to carry thermal or electrical energy ).They are easily hammered and bent into shape. They are typically lustrous/shiny solids (or liquids).

(b) High Melting Point and Boiling Point

The bonding between the atoms in transition metals is very strong (bonding notes). The strong attractive force between the atoms is only weakened at high temperatures, hence the high melting points and boiling points (again compare with Group 1 Alkali Metals).
Mercury is in another transition metal, but unusually, it has a very low melting point of -39oC. For example: iron melts at 1535°C and boils at 2750°C BUT a Group 1 Alkali Metal such as sodium melts at 98°C and boils at 883°C.
(c) High density

Another consequence of the strong bonding between the atoms in transition metals is that they are tightly held together to give a high density.
For example: iron has a density of 7.9 g/cm3 and sodium has a density of 0.97 g/cm3(and floats on water while fizzing! water has a density of 1.0 g/cm3).

Uses of Transition Metals and their compounds

Transition metals are extremely useful metals on account of their physical or chemical properties eg lack of corrosion and greater strength compared to the Group 1 Alkali Metals. Many are used in alloys (a mixture of metal with at least one other metallic or non-metallic substance). For catalysts - see above. Their strength and hardness makes them very useful as structural materials.

Cast iron is used for man-hole covers because it is so hard wearing but it is brittle due to a high carbon content.
When alloyed with 1% carbon iron forms mild steel which is not brittle, but is more malleable and corrosion resistant than cast iron. Mild steel is used for food cans, car bodies (but galvanising and several coats of paint help it to last!) and machinery etc.
Steel is an alloy based on iron mixed with carbon and usually other metals added too. There are huge number of steel 'recipes' which can be made to suit particular purposes by changing the % carbon and adding other metals e.g. titanium steel for armour plating.

Chromium steel (stainless steel, mixing and melting together Fe + Cr and maybe Ni too) with good anti-corrosion properties, used for cutlery and chemical plant reactors.

The alloy BRASS is a mixture copper and zinc. It is a much more hard wearing metal than copper (too soft) and zinc (too brittle) but is more malleable than bronze for 'stamping' or 'cutting' it into shape.
Copper is used in electrical wiring because it is a good conductor of electricity but for safety it is insulated by using poorly electrical conductors like PVC plastic.
Copper is used in domestic hot water pipes because it is relatively unreactive to water and therefore doesn't corrode easily.
Copper is used for cooking pans because it is relatively unreactive to water and therefore doesn't corrode easily, readily beaten or pressed into shape but strong enough, it is high melting and a good conductor of heat.
Copper is also used as a roof covering and weathers to a green colour as a surface coating of a basic carbonate is formed on corrosion.
The alloy BRONZE is a mixture of copper and tin (Sn) and is stronger than copper and just as corrosion resistant, e.g. used for sculptures.
Iron and steel are used for boilers because of their good heat conduction properties and high melting point.
Copper compounds are used in fungicides and pesticides e.g. a traditional recipe is copper sulphate solution plus lime is used to kill greenfly.
Copper is alloyed with nickel to give 'cupro-nickel', an attractive hard wearing 'silvery' metal for coins.
Steel, iron or copper are used for cooking pans because they are malleable, good heat conductors and high melting.

NICKEL is alloyed with copper to give 'cupro-nickel', an attractive hard wearing 'silvery' metal for coins.


Zinc is used to galvanise (coat) iron or steel to sacrificially protect them from corrosion. The zinc layer can be put on the iron/steel object by chemical (see electroplating and below) or physically dipping it into a bath of molten zinc.
Zinc sulphate solution can be used as the electrolyte for electroplating/galvanising objects with a zinc layer.
Zinc is used as a sacrificed electrode in a zinc-carbon battery. It slowly reacts with a weakly acidic ammonium chloride paste, converting chemical energy into electrical energy.
The alloy BRASS is a mixture copper and zinc. It is a much more hard wearing metal than copper (too soft) and zinc (too brittle) but is more malleable than bronze for 'stamping' or 'cutting' it into shape.
Transition metal compounds (often oxides) of copper, iron, chromium and cobalt are used to pigments for artwork, and give bright colours to stained glass and ceramic/pottery glazes e.g.
Paint pigments: chromium oxide Cr2O3 green, iron oxide (haematite) Fe2O3 red-brown, manganese oxide MnO2 black, copper hydroxide-carbonates (malachite-green, azurite-blue) and titanium dioxide TiO2 white.
Stained glass: cobalt oxide CoO blue, iron oxide/carbonate green, Cu metal red, CuO turquoise.
NICHROME is an alloy of chromium and nickel. It has a high melting point and a high electrical resistance and so it is used for electrical heating element wires.
NITINIOL: Titanium and nickel are the main components of Nitinol 'smart' alloys which are very useful intermetallic compounds. Nitinol belongs to a group of shape memory alloys (SMA) which can 'remember their original shape'. For example they can regain there original shape on heating (e.g. used in thermostats in cookers , coffer makers etc.) or after release of a physical stress (e.g. used in 'bendable' eyeglass frames, very handy if you tread on them!). The other main metal used in these

TUNGSTEN is used as the filament in light bulbs because its melting point is so high.
Transition metals like platinum and rhodium are used as metal catalysts in the catalytic converters used in car vehicle exhausts to reduce carbon monoxide and nitrogen oxide polluting emissions.
Bright, shiny and relatively unreactive copper, silver and gold are used in jewellery.
For material on coordination compounds on see


web sites
Transition Metal Elements

for more material on



JEE Question 2007 paper II

Statement - 1

Band gap in germanium is small.


Statement - 2

The energy spread of each germanium atomic energy level is infinitesimally small.

(A) Statement – 1 is True, Statement – 2 is True; Statement – 2 is a correct explanation for statement – 1
(B) Statement – 1 is True, Statement – 2 is True; Statement – 2 is NOT a correct explanation for Statement – 1.
(C) Statement – 1 is True, Statement – 2 is False
(D) Statement – 1 is False, Statement – 2 is True

Answer C

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