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Engineering CHEMISTRY

 TERM PAPER ON

 TRANSITION

ELEMENTS AND ITS

USES.

SUBMITTED BY: Sohail Maqbool

SUBMITTED TO: Nidhi Sethi

SECTION: G5001

ROLL NO: B-61

REGD NO: 11003601

 

AKNOWLEDGEMENT

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First and foremost I thank my teachers who have assigned me this term paper to bring out my

creative capabilities.

I express my gratitude to my parents for being a continuous source of encouragement and for 

their all financial aid given to me.

I have like to acknowledge the assignment provided to me by the library staff of LOVELY

PROFESSIONAL UNIVERSITY.

My hard felt gratitude to my friends for helping me to complete my work in time.

SOHAIL MAQBOOL

 

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CONTENTS

1. Introduction

2. Characteristic Properties

2.1 Coloured Compounds

2.2 Oxidation States

2.3 Variable Oxidation States

2.4 Magnetism

2.5 Other Properties

3. Importance Of Transition Elements

4. Reference Cited

Transition Elements

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Coloured compounds

Colour in transition-series metal compounds is generally due to electronic transitions of two

 principal types.

Charge transfer transitions. An electron may jump from a predominantly ligand orbital to

a predominantly metal orbital, giving rise to a ligand-to-metal charge-transfer (LMCT)

transition. These can most easily occur when the metal is in a high oxidation state. For example, the colour of chromate,dichromate and permanganate ions is due to LMCT

transitions. Another example is: Mercuric iodide, HgI2, is red because of a LMCT transition.

As this example shows, charge transfer transitions are not restricted to transition metals.

A metal-to ligand charge transfer (MLCT) transition will be most likely when the metal is in a

low oxidation state and the ligand is easily reduced.

d -d transitions. An electron jumps from one d-orbital to another. In complexes of the

transition metals the d orbitals do not all have the same energy. The pattern of splitting of 

the d orbitals can be calculated using crystal field theory. The extent of the splitting depends

on the particular metal, its oxidation state and the nature of the ligands. The actual energy

levels are shown on Tanabe-Sugano diagrams.

In centrosymmetric complexes, such as octahedral complexes, d -d transitions are forbidden by

the Laporte rule and only occur because of vibronic coupling in which a molecular 

vibration occurs together with a d-d transition. Tetrahedral complexes have somewhat more

intense colour because mixingd 

and p

orbitals is possible when there is no centre of symmetry,

so transitions are not pure d-d transitions. The molar absorptivity (ε) of bands caused by d-

d transitions are relatively low, roughly in the range 5-500 M−1cm−1 (where M = mol

dm−3). Some d -d transitions are spin forbidden. An example occurs in octahedral, high-spin

complexes of manganese(II), which has a d 5 configuration in which all five electron has parallel

spins; the colour of such complexes is much weaker than in complexes with spin-allowed

transitions. In fact many compounds of manganese(II) appear almost colourless. The spectrum

of [Mn(H2O)6]2+  shows a maximum molar absorptivity of about 0.04 M−1cm−1 in the visible

spectrum.

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Oxidation states

A characteristic of transition metals is that they exhibit two or more oxidation states, usually

differing by one. For example, compounds of vanadium are known in all oxidation states between −1, such as [V(CO)6]

−, and +5, such as VO3−4.

Main group elements in groups 13 to 17 also exhibit multiple oxidation states. The "common"

oxidation states of these elements typically differ by two. For example, compounds of gallium in

oxidation states +1 and +3 exist in which there is a single gallium atom. No compound of Ga(II)

is known: any such compound would have an unpaired electron and would behave as a free

radical and be destroyed rapidly. The only compounds in which gallium has a formal oxidation

state of +2 are dimeric compounds, such as [Ga2Cl6]2−, which contain a Ga-Ga bond formed from

the unpaired electron on each Ga atom.[11]

Thus the main difference in oxidation states, betweentransition elements and other elements is that oxidation states are known in which there is a

single atom of the element and one or more unpaired electrons.

The maximum oxidation state in the first row transition metals is equal to the number of valence

electrons from titanium (+4) up to manganese (+7), but decreases in the later elements. In the

second and third rows the maximum occurs with ruthenium and osmium (+8). In compounds

such as [MnO4]− and OsO4 the elements achieve a stable octet by forming four covalent bonds.

The lowest oxidation states are exhibited in such compounds as Cr(CO)6 (oxidation state zero)

and [Fe(CO)4]2− (oxidation state −2) in which the 18-electron rule is obeyed. These complexes

are also covalent.

Ionic compounds are mostly formed with oxidation states +2 and +3. In aqueous solution the

ions are hydrated by (usually) six water molecules arranged octahedrally.

Variable oxidation state :-

Zn +2

Cu +1 +2 +3

  Ni +1 +2 +3 +4Co +1 +2 +3 +4 +5

Fe +1 +2 +3 +4 +5 +6

Mn +1 +2 +3 +4 +5 +6 +7

Cr +1 +2 +3 +4 +5 +6

V +1 +2 +3 +4 +5

Ti +1 +2 +3 +4

Sc +3

1. Increase in the number of oxidation states from Sc to Mn. All possible states exhibited by

only Mn.

2. Decrease in the number of oxidation states from Mn to Zn, due to the pairing of delectronsoccurs after Mn. (Hund's rule).

3. Stability of higher oxidation states decreases along Sc to Zn. Mn(VII) and Fe(VI) are

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powerful oxidizers.

4. Down the group, the stability of high oxidation states increases (easier availability of 

both d and s electrons for ionization).

Magnetism

Transition metal compounds are paramagnetic when they have one or more unpaired d electrons.[12] In octahedral complexes with between four and seven d electrons both high spin and low

spin states are possible. Tetrahedral transition metal complexes such as [FeCl4]2− are high

spin because the crystal field splitting is small so that the energy to be gained by virtue of the

electrons being in lower energy orbitals is always less that the energy needed to pair up thespins. Some compounds are diamagnetic. These include octahedral, low-spin, d 6 and square-

 planar d 8 complexes. In these cases, crystal field splitting is such that all the electrons are paired

up.

Ferromagnetism occurs when individual atoms are paramagnetic and the spin vectors are aligned

 parallel to each other in a crystalline material. Metallic iron and the alloy alnico are examples of 

ferromagnetic materials involving transition metals. Anti-ferromagnetism is another example of 

a magnetic property arising from a particular alignment of individual spins in the solid state.

Other Properties

As implied by the name, all transition metals are metals and conductors of electricity.

In general transition metals possess a high density and high melting points and boiling points. 

These properties are due to metallic bonding by delocalized d electrons, leading

to cohesion which increases with the number of shared electrons. However the group 12 metals

have much lower melting and boiling points since their full d subshells prevent d-d bonding. Infact mercury has a melting point of -39 °C and is a liquid at room temperature.

Many transition metals can be bound to a variety of ligands. Some transition metals are useful in

homogeneous and heterogeneous catalysis. For example, iron is a catalyst in the Haber 

 process for ammonia synthesis, while nickel and platinum are used in hydrogenation of alkenes.

The Importance of d-block Transition Metals :-

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The d-block transition metals have great importance in our lives. They are building blocks

for life and are found directly in the center of the periodic table. The d-block simply means that

the elements’ d-orbitals are the last to get occupied according to the building-up principle. The

transition metals give off electrons from their outer s orbital, but most can lose a multiple

number of d orbital electrons. Because of this many of the d-block metals have multiple

oxidation numbers. A good example is copper which has two common oxidation states +1 and

+2. This causes d-block metals to make great catalysts.

Transition metals, for the most part, are good conductors. They are also malleable, ductile,

lustrous, and sliver-white in color. An exception to this would be copper, which is brownish red

in color. Metals have another great characteristic, they easily mix. This is because all the d-block 

metals have about the same atomic size. This allows them to replace one another easily in a

crystal lattice. When two or more metals mix, or replace one another, we call the new metal an

alloy. Brass is a good example of an alloy, which comes from copper and zinc combined.

These elements and alloys are fundamental for the existence of life, and also for its progression

through time. The d-block metals, and some of it’s key alloys, shaped the Bronze Age, Iron Age,and most importantly the steel age. Now with the booming of technology and the aerospace

industry, metals with high conductivity and large strength to weight ratios are at top demand.

Without these precious, durable, and sometimes highly valued metals, life simply would not

exist.

Transition metals are found everywhere on Earth in various amounts. Most are not found

in a pure substance, but rather in compounds buried in the Earth’s crust. This means that we

must extract the metal from the compound in one of two ways. One process

is pyrometallurgical which is when you use extremely high temperatures. The other is

hydrometallurgical if you used aqueous solution.

Sometimes it takes only one step but many times multiple steps are mandatory. For 

example, iron is found abundantly in two dominant ores in the Earth’s crust: hematite Fe2 O3 and

magnetite Fe3 O4. The ore is put into a blast furnace with some coke and limestone. The

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limestone then decomposes to form calcium oxide and carbon dioxide. The calcium oxide helps

remove the nonmetal oxide and amphoteric impurities from the ore. The mixture is all liquid so

the denser molten iron floats on the bottom. The mixture on top is simply drawn off and you are

left with pig iron. Pig iron is almost pure iron. It is contaminated with small amounts of carbon

and silicon.

Some metals that are rare can be sold at extremely high prices, such as gold. Other metals

are found right in front to you. That computer is full of transition metals. It has to have metals in

it to send electrical currents. How about your chair, it has metal ball-bearings in the wheels. Or 

the pictures hanging on the wall, they are hanging by nails, which are made from metal alloys.

Almost everything around you is made from transition metals. Titanium is a relatively new

transition metal that is in high demand due to its light weight, great strength, and high

temperature and corrosion resistance. It is used to make airplane bodies and engines. Other 

temperature resistant metals are used to make blast furnaces and high temperature technology

that can withstand extreme temperature changes.

Transition metals have always been on Earth. They have helped humans evolve through

time. When humans learned how to make bronze from copper and tin they started the Bronze

Age. Then came the Iron Age when higher processing temperatures became available. With

higher temperatures came iron reduction.Finally the age of industry, and with it, the demand for 

steel.

In today’s society transition metals are in their highest demand ever. Steel is used to

make bridges, buildings, and even works of art. Almost all of the skyscrapers have steel

skeletons. Steel can not only be used independently; it can be mixed with other compounds or 

elements, such as carbon to give certain effects. If you add less than .15% carbon the alloy is

ductile like iron wire. If the percentage is between .15 - .25% the alloy is much stronger. This

alloy is used to make cables, chains, and nails. If the percentage is between .20 - .60% the alloy

is mostly used for girders, rails, and structural purposes. If the percentage is .61 - 1.5% it is

considered high-carbon steel. This is used to make knives, razors, cutting tools, and drill bits. As

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you can tell it takes only small changes in the concentration of ingredients to make large changes

in the characteristics of the alloy.

Metals are also the key ingredient in automobiles because of their strength, durability,

and extreme resistance to heat and fire. Metals are used to make bicycles, electrical

toothbrushes, wires, refrigerators, and anything else that has metal parts. Anything that needs

electricity has metal components because metals are electrical conductors. Battery casings,

scissors, and microwaves are a few more examples of objects that are made from metals.

The main problem with transition metals is their readiness to oxidize. When they oxidize

the metals corrode and become brittle. This is easily overcome by simply covering up, so they

don’t come in contact with oxygen. Iron is a good example of this because it is used to make car 

 bodies. If they didn’t paint cars they would all rust and the iron car body would fall apart.

Coincidently when your paint scratches off rust forms there and the rust will eventually become

 brittle and fall off. Not all metals form oxides and become brittle. For instance, Titanium is

corrosive resistant because it forms a protective skin when the exterior is exposed to oxygen.

When the exterior is exposed oxides are formed. Once this occurs no further oxidizing takes

 place because oxygen can not get past the already formed oxides. The last way to stop the metals

from oxidation is by making alloys. Alloys of chromium, for example, have a higher corrosion

resistance than that of most alloys; they are given the name, stainless (i.e. stainless steel).

Transition metals are used as catalysts in many ways. We use metal surfaces with oxides

to make ammonia. This is the most economical way to produce ammonia, and is highly used in

fertilizers. The metal surface can adsorb elements and compounds into itself. Once this occurs

 bonds break between elements so they adsorb into the metal. Since the elements can move

around they end up colliding together with enough energy to form a bond between each other 

and break the adsorption bond. It is in this fashion that ammonia in produced. This is not the

only way metals can be used as a catalyst. Many times transition metals can be used to simply

speed up a reaction. This is used because it is often economically cheaper to add some metal

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rather than waste time waiting for the reaction to occur. An example of this would be the use of a

vanadium oxidizing catalyst in the process the making sulfuric acid.

We also use transition elements in many other ways. They are the key to making

different colored paints, photo reactive eye glasses, and mercury thermometers. Titanium is used

to detect underwater sound. Barium titanate is piezoelectric, which means that it generates an

electrical charge when it is mechanically distorted. When the sound wave hits the compound it

mechanically vibrates generating an electrical signal. Some like iron, cobalt, and nickel produce

a magnetic effect called ferromagnetism and are used for permanent magnets and magnetic

devices. Ferromagnetism is an effect similar toparamagnetism which occurs when an element

has an unpaired electron. The electrons in paramagnetism are spinning randomly causing a much

weaker effect. With ferromagnetism, the unpaired electrons have aligned spins forming domains

that survive even after the applied field is turned off. For this reason ferromagnetic materials are

used in coating cassette tapes, computer disks, and other devices that use magnetic codes and

signals. We also use them to turn sunlight into electricity. Things like copper 

indium diselenide (CIS), and cadmium telluride (CdTe) can be found in photovoltaic solar cellsused to convert solar energy into heat energy and eventually it is converted into electrical

energy. For more on solar energy check outhttp://www.solaraccess.com/education/solar.jsp?

id=pv

Transition metals are also found in our bodies. Humans excrete about 1 mg of iron every

day and must constantly have approximately three grams of iron in their bodies. The iron is

mostly used as hemoglobin, which transports oxygen to the brain and muscles. Iron deficiency,

or anemia, occurs when your body doesn’t have enough iron and causes one to become

chronically tired. Cobalt is another transition metal our bodies need. It is a component of vitamin

B12 which humans need in their diet.

The transition elements have hundreds of responsibilities. They are key elements in life

and evolution. Without iron, oxygen wouldn’t make it to the brain and life would not exist. The

 bronze, iron, and steel ages would never have happened leaving us in the Stone Age. Transition

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metals have become of utmost importance due to our every growing population and economy.

Their demand will continue as long as life as we know it continues.

 

References Cited :-

1. Chemistry 4th Edition Molecules, Matter, and Change. Jones, Loretta and

Atkins, Peter. Chapter 21 mostly.

2. www.chemicalelements.com/groups/transition.html

3. www.solaraccess.com/education/solar.jsp?id=pv

4. http://naio.kcc.hawaii.edu/chemistry/transition_metals.html

5. www.wikipedia.com/en/transition elements

6. www.britannica.co.us/transition elements

7. Raymond Chang 4th Edition

8. Dinesh +2 Chemistry In Action

9. Pradeep Chemistry +2