The Chemical Properties Of Transition Metals Biology Essay

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If you are a fan of anything that is shiny, then you are never far away from a metal. Like any other teenager, I have always liked wristwatches and cars, but it never occurred to me until when I was eleven that they are all made up of the same material which was a metal. It was then I started to value it even more and I became more curious about metals. As a kid, I use to think all metals were 'iron', well, typical from where I grew up. But iron to my greatest surprise, is from a particular family of elements known as transition elements otherwise known as the transition metals.

Transition metals are so far the most useful set of elements known to man. They have a vast area of application, e.g. the blood contains iron and shortage of it causes iron deficiency anemia a sickness which usually results to death. The significance of these elements cannot be over emphasized and that was why I choose to write on transition metals.

The Bronze Age

In the early years of man, there were no shelters, proper clothing or packaged food you can prepare to eat like there is in the modern world. These conditions forced man to find a way to feed, which was by hunting. To hunt, man had to cave stones and rocks to make weapons. Inside some of these rocks were what was known as 'native metal'. They are metals in their uncombined states.

Usually after campfire, or when rocks are heated to high temperature, native metal flows out through cracks and onto the surface of the rock. Such metals include gold, copper, aluminum and so on.

Our ancestors used the metals for mostly ornamental purposes. With time, they got to find out that some metals could be more useful than just for ornamental purposes e.g. copper was harder than gold and silver, and yet, it was easier to carve into spoons, knives and arrows. After some time, they figured out how to obtain these metals by heating rocks. Although copper was the most useful then, it existed as a compound. Which meant extracting it would require another compound that will separate it from the other elements. But, in no time, our ancestors figured out how to extract the copper alone which was by using charcoal to heat the rock.

Some batches of copper were harder, thus they were used mainly for tools and weaponry. The reason for their being hard was that tin compounds were occurred in the ores of copper compounds and during smelting, the result would be a mixture of both tin and copper ; an alloy termed Bronze will be the end result.

Although copper was strong, bronze was even stronger. Tool made from bronze were stronger and all tools made then were mostly used in the farm and better tools meant better food production rate, Also stronger arrow and spares meant easier hunting. And from there history changed its cause towards the today world. People then started to have time to practice other professions like pottery statue making and so on than wasting the whole day in the farm. This period was then termed the BRONZE AGE.

TRANSITION ELEMENTS

According to Chris Conoley and Phill Hills, they defined transition elements as 'elements that form one or more ions with a partially filled d-subshell'. (2008, pg481). Transition elements are located between group two and group three. In fact, they form a large percent of the families of elements in the periodic table. Transition metals are classified into series. Those in period four i.e. from scandium to zinc are known as the first series transition metals likewise those in period five are known as the second series transition elements and it goes on that way.

This write up will cover the first series transition element and ……

The first series transition metals include;

Scandium and Zinc are not considered to be ordinary metals. This is because zinc forms only one stable ion with a completely filled d-orbital while scandium on the other hand forms also only one stable ion with an empty d-orbital.

From the diagram of electronic configuration above, we find out that copper and chromium have an unusual electronic configuration. They have only one electron in their 4s subshell.

This is because before chromium is reached, the number of protons increases by one and at the same time electron number too in the d-subshell increase by one electron. According to Chris Conoley, there is a jump of two electrons, one of which is from the 4s-subshell. He further explained that the half filled subshell has five singly occupied orbitals. (2008, pg482). Therefore, this arrangement is considered to be at lower energy ( 3d5 4s1) and this reduces repulsion in the 4s orbital between electrons.

In the case of copper, the electronic configuration is most stable at 3d10 4s1.

Properties of transition metals

Transition metals in terms of their physical properties exhibit the same properties that ordinary metals portray which include; having high metals, they are strong, hard and are dense. They are sonorous, malleable and ductile. They luster when polished and they are excellent conductors of electricity.

CHEMICAL PROPERTIES

The chemical properties of transition metals are what make transition elements unique and they include;

Variable oxidation states

Xplain

Lower oxidation states in ionic compounds

Transition metals have a wide range of loss of electron. Unlike group one and two elements where all the elements can only loose one electron (i.e. elements in group one) or two electrons (i.e. elements in group two), transition can first empty their 4s shell before the 3d shell. That is why the +2 oxidation state is common in with the transition metals. However, the 3d electrons can also be lost and for that ions of +3 are also common. Examples include Fe2+, Co2+, V3+ , Cr3+ and so on are common.

elements

Electronic configuration

ΔHi(1)

ΔHi(2)

ΔHi(3)

ΔHi(4)

Ca

1s2 2s2 2p6 3s2 3p6 4s2

590

1145

4912

6474

Fe

1s2 2s2 2p6 3s2 3p6 3d6 4s2

759

1561

2958

5290

From the above table, a giant leap is noticed from the third ionization of calcium. This is because the third electron is located 3p shell which further away. But I case of iron, a gradual increase is obverted because the 4s and 3d shells are very close and thus formation Fe2+ and Fe3+ is easier.

Higher oxidation states

The maximum oxidation number of the first transition series is +7 which is found in manganese. However, high oxidation number such as +7, +6, and +5 would be too polarizing to exist and it will require a lot energy to obtain. But such high oxidation states can be found in some covalent bonds and sometimes in ions example include; Ti with oxidation number of +4 in TiO2, vanadium with +5 in V2 O5 and in VO2+, chromium with +6 in CrO3 and in Cr2O72-, and manganese with +7 in Mn2O7 and in MnO4-.

The maximum oxidation state is reached at manganese, therefore, all the oxidation states starts decreasing as you move to the right of manganese. This is because increasing energy needed to involve 3d electrons in bonding, and because singly filled orbitals are required in order to form a covalent bond.

Naming transition metal compounds and ions

Sodium has only one oxidation state, which is why we can call it sodium chloride in its chloride or sodium carbonate in it carbonate. In general, it is easy to name compounds with only one oxidation state.

In transition metals, where they exhibit multiple oxidation states, the metal's oxidation state has to be determined. This is done by first assuming the oxidation state of the transition metal to be 'x'. Then equating the sum of oxidation states of the elements present in the compound and 'x' to the charge on the compound. Example;

The oxidation state iron in FeCl3 is given by:

Let the oxidation state of Fe in FeCl3 be x

Thus, oxidation state of Fe in FeCl3 is +3.

After calculating the charge, the compound is named by the naming the transition metal together with its oxidation state and the other elements follow. In the above example, the compound is named as Iron (III) chloride.

Complexes

The presence of lone pairs of electrons surrounding a central metal atom or ion results to what is known as complex. These lone pairs are donated by a species of molecules called ligand. Ligands are usually molecules such as water, ammonia, hexacynoferite and so on. Like any other compound or ion, complexes can either be neutral, or charged. The charge on a complex depends on the sum of charge of the central metal and the charge on the surrounding ligands all together.

Uses of some complexes

Test for Cu2+

{Ag (CN)2}- is used in electroplating

{Ag (NH3)2}+ is used in testing for aldehydes because it is a strong reducing agent.

Shapes of complexes

The formation of colored ions

Transition metals compounds are colored and they react with solutes to form colored solutions. Below are some colors of common aqueous ions of the transition metals.

Ion

Color

Outer 3d electrons

Sc3+(aq)

Colorless

3d0

Ti3+(aq)

Purple

3d1

V3+(aq)

Green

3d2

Cr3+(aq)

Violet

3d3

Mn2+(aq)

Pink

3d5

Fe3+(aq)

Yellow

3d5

Fe2+(aq)

Green

3d6

Co2+(aq)

Pink

3d7

Ni2+(aq)

Green

3d8

Cu2+(aq)

Blue

3d9

Zn2+(aq)

colorless

3d10

The color of the ion is as a result of the partially filled d-orbital where some components of white light are absorbed and some are being reflected. However, the type of ligand that bonds to these metals can alter the color of ion. An typical example is case of {Cu(H2O)6}2+ is paler than the amine complex {Cu(NH3)4(H2O)2}2+ which deep blue in color. This feature of transition metals makes it possible to identify the presence of an element in an unknown compound.

Catalysis of transition metals

Catalysts are substances that alter the rate of chemical reaction without taking part in the reaction i.e. they are regenerated at the end of the reaction. A catalyst basically reduces the activation energy of the reacting moles; in most cases speeding up the reaction rate.

There two types of catalytic processes; heterogeneous and homogeneous catalysis.

Heterogeneous catalysis

Fe

Consider the haber process which it used in preparation of ammonia. It involves the use of finely divided iron to catalyze the reaction.

N2(g) + 3H2(g) 2NH3(g)

The catalyst iron is in the different phase (solid) to the reactants and products, thus in this case, the catalytic process is referred to say heterogeneous catalysis.

According to Chris Coloney, heterogeneous catalyst works by providing a surface on which the reactants can form weak bond. These are called active series. Transition metals use their 3d and 4s electrons to make these bonds. (2008, pg; 497)

Homogeneous catalysis

In a nutshell,

Transition elements are d-block elements; their valence electron occupies a d-subshell.

They are paramagnetic; they alter the lines of force of a magnet

They have variable oxidation states; they have a wide variety of option in loss of electrons

Formation of complexes; transition metals can empty their 4s shell making it available for molecules containing a lone pair of electrons called ligand to donate the electron and form complex ions by dative covalent bond.

Formation of colored solution; transition metals have the ability to absorb some component of white light into its partially filled d-orbital and reflect others. The reflected once are the colors in which the metal appears.

Used as industrial catalyst; transition metals are useful Industrial catalyst.

Fe

The haber process is it used in preparation of ammonia. It involves the use of finely divided iron to catalyse the reaction.

N2(g) + 3H2(g) 2NH3(g)

The above reaction is a very important industrial reaction because if forms the basis of formation of fertilizers.

V2O5

The contact process is the first step when preparing sulphuric acid and thus it is also an important reaction in chemistry.

2SO2(g) + O2(g) 2SO3(g)

Pt

Other reactions include;

2CO(g) + O2(g) 2CO2(g)

Ni

Oil + H2(g) Fats

MnO2

2H2O2(L) 2H2O(g) + O2(g)

MANGANESE

Atomic number

25

Atomic mass

54.9380 g.mol -1

Oxidation states

+7,+6,+5,+4,+3,+2,+1,-1,-2,-3

Electronegativity according to Pauling

1.5

Density

7.43 g.cm-3 at 20°C

Melting point

1247°C

boiling points

2061°C

Vanderwaals radius

0.126nm

Ionic radius

0.08 nm (+2) ; 0.046 nm (+7)

isotopes

7

Electronic shell

[ Ar ] 3d5 4s2

Energy of Second ionization

716 kJ.mol -1

Energy of Second ionization

1489 kJ.mol -1

Standard potential

- 1.05 V ( Mn2+/ Mn )

Discovered by

Johann Gahn in 1774

Occurrence

Manganese is one of the world's most abundant metal. Is exists mainly as pyrolusite (MnO2) and rhodochrosite (MnCO3).

Extraction

Manganese is extracted

Biological importance

Manganese is a very important element that is necessary for human survival. According to an article published by Technical University of Delft, it says that excess manganese is toxic to the body whilst at the same time low intake of manganese leads to several health associated illnesses like Parkinson, bronchitis, hallucinations nerve damage and so on.

The main source of manganese to humans is during feeding. According to an article published by the University of Maryland Medical Center, it says that women reauire a minimum of 1.8mg per of manganese per day while men require a minimum of 2.3mg per day. Foods, mainly grain, nuts, have the highest concentration of manganese. When these foods are in our system, they are being transported by the blood to the liver. Manganese in the body helps with formation connective tissue, bone, sex hormones enzymes and synovial fluid in the joints. Manganese in the body is also used in processing thiamin. In animals, manganese is an essential component that enhances over thirty-six enzymes that are used for different body metabolisms.

Manganese is also important for plant survival. Manganese is transported to the leaves in form of ions where it contributes to the division of water into oxygen and hydrogen during photosynthesis. Thus manganese plays a very important role in plants.

Purification

Industrial significance

Manganese is a very useful metal. It suits best for production of metallurgical alloys because it helps eliminate impurities such as oxygen and sulfur from other metals and its alloys are strong and less corrosive. Manganese is also used in making disposable battery.

Manganese is dangerous because it can also be used in food poisoning.

Recommendation

A critical study of manganese can pave way to help those with neurological associated problems because most neutral activities have something to do with manganese.

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