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Transition metals

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Introduction

Transition metals Common properties The transition metals have these properties in common: * They are metals. * They form coloured compounds. * They are good conductors of heat and electricity. * They can be hammered or bent into shape easily. * They are less reactive than alkali metals such as sodium, they have higher melting points (but mercury is a liquid at room temperature) and they are hard and tough. * They have high densities. Iron The chemical symbol for iron, Fe, comes from the Latin word for iron - ferrum. Iron is the second most abundant metal in the Earth's crust (aluminium is the most abundant metal). The core of the Earth is solid iron, and iron is found in meteorites, but in the Earth's crust iron is found mainly as minerals of iron oxide - hematite, magnetite, goethite and limonite. The mineral which is mostly used as ore for making iron is hematite. Its chemical formula is Fe2O3. Iron is about 8 times heavier than water (its relative density is 7.87). When iron is exposed to the air it starts to turn back into iron oxide and the red powder that forms on the surface of iron is what we call rust. You may have seen rust on old cars or old iron sheds or roofs. ...read more.

Middle

It is twice as strong as aluminium. It is nearly as resistant to corrosion as platinum. Titanium is a component of joint replacement parts, including hip ball and sockets. It has excellent resistance to sea water and is used for propeller shafts, rigging, and other parts of ships exposed to salt water. A titanium anode coated with platinum provides cathodic protection from corrosion by salt water. Titanium paint is an excellent reflector of infrared radiation, and is extensively used in solar observatories where heat causes poor viewing conditions. Pure titanium dioxide is relatively clear and has an extremely high index of refraction with an optical dispersion higher than diamond. It is produced artificially for use as a gemstone, but it is relatively soft. Star sapphires and rubies exhibit their asterism as a result of the presence of TiO2. The dioxide is used extensively for paint as it is permanent and has good covering power. Titanium oxide pigment accounts for the largest use of the element. Copper The word copper comes from the Latin word "cuprum", which means "ore of Cyprus". This is why the chemical symbol for copper is Cu. Copper is the only naturally occurring metal other than gold that has a distinctive colour. Like gold, copper is an excellent conductor of heat and electricity. ...read more.

Conclusion

As an example of a different pathway, when propanone (H3C - CO - CH3) is reacting with iodine in water, it reacts faster in acid conditions. Protons in solution are a catalyst of the reaction. With acid conditions, the propanone is more likely to be protonated which allows a different and lower activation energy pathway to the iodination of the propanone. Many transition metals are used directly as catalysts in industrial chemical processes and in the anti-pollution catalytic converters in car exhausts. For example iron is used in the Haber Synthesis of ammonia: Nitrogen + Hydrogen ==> Ammonia (via a catalyst of Fe atoms) or N2(g) + 3H2(g) ==> 2NH3(g) Platinum and rhodium (in other transition series below Sc-Zn) are used in the catalytic converters in car exhausts to reduce the emission of carbon monoxide and nitrogen monoxide, which are converted to the non-polluting gases nitrogen and carbon dioxide. 2NO(g) + 2CO(g) ==> N2(g) + 2CO2(g) Nickel is the catalyst for 'hydrogenation' in the margarine industry. It catalyses the addition of hydrogen to an alkani carbon=carbon double bond (>C=C< + H2 => >CH-CH<). This process converts unsaturated vegetable oils into higher melting saturated fats which are more 'spreadable' with a knife! As well as the metals, the compounds of transition metals also acts as catalysts. For example manganese dioxide (or manganese(IV) oxide), MnO2, a black powder, readily decomposes an aqueous solution of hydrogen peroxide: Hydrogen peroxide ==> water + oxygen or 2H2O2(aq) ==> 2H2O(l) + O2(g) ...read more.

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