Transition Metal

Many scientists describe a transition metal as any element in d-block of the periodic table. They occupy the middle portion of the long periods of the periodic table between the groups on the left-hand side and the group on the right (from group 3 to group 12). The most striking similarity shared by these elements is that they are all metals. The most of them are hard, strong and lustrous. They are good conductors of heat and electricity and these metals have high melting and boiling points. Many of these metals are technologically important such as: titanium (Ti), iron (Fe), nickel (Ni) and copper (Cu). They are used for alloys production, with one other or with other metallic elements. Most of transition metals can be dissolved in mineral acids. Platinum (Pt), silver (Ag) and gold (Au) are called noble because they are unaffected by non oxidizing mineral acids.

These metals may be subdivided into three series named fist, second and third main transition series. The lanthanoids and the actionoids make two particular series called inner transition series. First main transition series begins with scandium (Sc, atomic number 21) and ends with zinc (Zn, atomic number 30). Second one begins with yttrium (Y, atomic number 39) and ends with cadmium (Cd, atomic number 48). Finally, third series includes the elements hafnium (Hf, atomic number 72) to mercury (Hg, atomic number 80). Some of transition metals are rare in the nature, but some of them occur in high concentration in the Earth's crust. Iron is the cheapest and one of the most abundant of all metals, comprising nearly 5.6% of Earth's crust and almost whole Earth's core. Iron (Fe) is primarily obtained from the minerals hematite (Fe2O3) and magnetite (Fe3O4). The minerals taconite, limonite (FeO(OH) x nH2O) and siderite (FeCO3) are other important sources. The estimated crustal abundance is 5.63x104mg/kg and the number of stable isotopes is 4. The most often oxidation states are +2 and +3. Copper (Cu) is primarily obtained from the ores cuprite (Cu2O), chalcocite (Cu2S), covellite (CuS), etc. Copper comprises just 1.4x10-4 % of the Earth's crust. Copper may be found in the nature as an element.  The estimated crustal abundance is 6.0x101mg/kg and the number of stable isotopes is 2. The oxidation states are +1 and +2. Copper (Cu) and Iron (Fe) are probably the two most important metals for technical purposes. The main ores of zinc (Zn) are sphalerite (ZnS) and smithsonite (ZnCO3). Zinc mass fraction in the Earth's crust is 1.0x10-4%. The number of stable isotopes is 3, and the oxidation state is +2. Silver (Ag) can be obtained from pure deposits, from silver ores such as argentite (Ag2S) and horn silver (AgCl) and in conjunction deposits of ores containing lead, gold and copper. There is a small quantity of silver in the nature, mass fraction is about 10-8%. Silver has 2 stable isotopes and the oxidation state +1. There is only one mineral that contains significant of cadmium (Cd) - greenockite (CdS). The small amounts of cadmium are found in zinc ores as sulfides and carbonates. Cadmium is a rare metal, the estimated crustal abundance is 1.5x10-1mg/kg. Cadmium has 3 stable isotopes and the oxidation state +2. Gold (Au) is sometimes found free in the nature, but it can be found in conjunction with silver, quartz (SiO2), calcite (CaCO3), lead, tellurium, zinc or copper. Gold is a rare chemical element. Gold is the most malleable and ductile of all known metals. The estimated crustal abundance is 4.3x10-3mg/kg, the number of stable isotopes is 1 and the oxidation states are +1 and +3. Mercury (Hg) sometimes may found free, but it is usually obtained from the mineral cinnabar (HgS). Mercury has 7 stable isotopes. The oxidation states are +1 and +2 and the estimated crustal abundance is 8.5x10-2mg/kg.

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The general electronic configuration of d-block elements (transition metals) is [electronic configuration of noble gas] (n-1)d1-10 ns0-2. For the transition metals in the 6th and 7th periods should be added (n-2)f0-14. It is important to see that the transition metals have different number in 3d, 4d and 5d orbital, but all of them have 2 electrons in the most outer energetic shell (exceptions are chromium and copper). Because of these 2 electrons almost all transition metals form compounds wit oxidation state +2.  

Properties of transition metals include:

• have large charge/radius ratio;
• they are all metals;
• are hard and have high densities;
• have high melting and boiling points;
• form compounds which are often paramagnetic;
• shows variable oxidation states;
• form colored ions and compounds;
• form compounds with profound catalytic activity;
• form stable complexes.

Transition metals demonstrate a wide range of chemical behaviors. Some of them are strong reducing agents, but on other hand metals like platinum and gold have the ability to resist the oxidation which makes them valuable. The reactivity of the transition elements varies widely from very active metals such as scandium and iron to almost inert elements such as the platinum metals. Transition metals can form compounds with a wide range of the oxidation states. The bonding in the simple compounds of the transition elements ranges from ionic to covalent. They can form halides with halogens such as FeCl2 (iron(II) chloride) and FeCl3 (iron(III) chloride). The examples of the other compounds are oxides [Cr2O3 (chromium(III) oxide), CuO (copper(II) oxide), FeO (iron(II) oxide)], hydroxides [Co(OH)2 (cobalt(II) hydroxide), Ni(OH)2 (nickel(II) hydroxide), Fe(OH)3 (iron(III) hydroxide)], carbonates, sulfates etc.

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The uses of the transition metals are wide and varied. They appear in the almost every facet of our day to day life, from electric cabling to decorative door handles to corrosion resistant alloys. Hence the transition metals are extremely important elements. Iron finds use in production of the enormous varieties of steels. It is very important economically and of course it is used in construction industry, manufacturing of machines, cars, etc. It is the essential building block of hemoglobin in the bloodstream of animals and humans. Copper's major use is as conductor of electricity for electric cable production. It is also used for coins and alloys production. Zinc is used as anti corrosion coating (e.g. galvanized steel) as well as in alloys and batteries production. The main use of chromium is in the production of non-ferrous alloys. Manganese is used to increase the hardness of steel and in the production of non-ferrous alloys. Titanium major uses in the aircraft industry, for airframes and engines, bur chemical processing and marine equipment is also an important use. Titanium alloys are also used in hip replacement and bone implants, due to the law reactivity of the alloys. Nickel is used in the production of alloys. Stainless steel contains up to 8% of nickel.

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