2.4 Transition Metals
Transition metals are the elements you can find in the center block of the periodic table. It consists of metals and some of these metals I am sure you use or see daily in your life. For example, Au (gold), Ag (silver), Cu (copper), Fe (iron), etc.
Transition metals show physical properties that are sort of the opposite of the alkali metals.
They have high densities, high melting points, are malleable and ductile and are good conductors of electricity and heat.
Lets look at the chemical properties:
Transition metals are relatively not very reactive metals, unlike alkali metals. For example gold and silver are used in jewellery and electronics for this very reason. This means that they are stable under normal conditions (wont react with air or water) and can be used for various applications (electronics, constructions, jewellery, etc) However, not all transitions metals are unreactive in air, for example iron rusts very easily. But with some tweaking we can take iron and convert it to make stainless steel which is relativley rust proof.
Rusted iron plate. The brownish compound is iron (III) oxide and is known as ferric oxide.
Some of the transition metals have variable valency, that is they don't have a fixed valency. For example, copper can ionize to turn into either a 1+ or 2+ cation and iron can ionize to form either 2+ or 3+ cations. Therefore, they can form more than one type of a compound by reacting with the same element or molecule. Furthermore, since some of the properties for each ionic state of the transition element is different, the product's uses also changes.
For example iron reacts with oxygen to form two separate compounds. One is FeO which is iron (II) oxide and is known as ferrous oxide. The other is Fe2O3 which is iron (III) oxide and is known as ferric oxide. Ferrous oxide is a black powder used in the production of paper, glass, ceramics, plastics, etc. Whereas ferric oxide is reddish brown used in the production of steel, cosmetics, medicine, etc.
You might have noticed that FeO and Fe2O3 are colored compounds. Some transition metals form colored compounds and if the particular metal has more than one ionic state, like Fe, then the color of the compound formed also changes depending on the ionic state. Another example is copper. Cu2O (copper (I) oxide) is called cuprous oxide and CuO (copper (II) oxide) is called cupric oxide; they have different colors. Cuprous oxide is red and cupric oxide is black in color.
The reason they produce different colors has to do with the electron configuration of each of these ions. We will talk about how these colors are produced later on.
Some transition metals also form complex ions. Complex ions are, just as the name suggests, ions that are complex meaning they are made up of alot of atoms or molecule. Normally when you try to picture an ion, you think of a single atom or two different atoms that have lost or gained an electron to form an anion or cation. For example: H+, OH-, SO4-, CO3-, etc. But complex ions are sort of very large molecules that have turned into an anion or cation. Lets look at an example:
Let's say we add ammonia, NH3, to a solution of copper(II). The solution of copper (II) is blue in color because Cu2+ ions forms a blue color solution. The product we get in this reaction is a pale blue copper (II) hydroxide precipitate. The reaction is shown below. A precipitate is a solid that does not dissolve in the solution but stays a solid. Its just like having a piece of stone in a cup of water. We will discuss the properties of precipitates, like solubility in acids etc, in detail later on. What's happened in this reaction is that some of the copper ions have joined together with hydroxide ions to form an insoluble solid.
However, if we keep adding ammonia, this insoluble solid completely disappears forming a blue solution. What do you think has happened for the precipitate to disappear? Did the precipitate just break apart so that copper can dissolve again in the solution? Not really.
The precipitate has turned into a complex ion which has dissolved to give a deep blue color. What happens after we add ammonia is that the copper 2+ cations get greedy. They attract 2 molecules of water and 4 molecules of ammonia to form a large 2+ cation. The formula for this large complex ion is shown below. This complex ion is soluble therefore dissolves in the solution. The reason they do this is beyond the scope of IGCSE so I wont get into the details behind it. Just know that before we added a lot more ammonia, there weren't enough ammonia molecules for copper to act on its greed. The reason behind the deeper color is the ammonia that has bonded onto the copper ions. The chemistry behind this color intensity is a little hard for this level.
Transition metals are dense and strong structures. They don't break under heavy loads; therefore, are ideal for construction. Some of these metals can be tweaked to improve strength and gain other desirable properties. An example of this is iron being converted to steel and other allows. Steel is widely used in building large structures because of its strength and economic feasibility. Steel is made by removing impurities from iron ore and adding a very small amount of carbon.
Transition metals are very good conductors of heat. Therefore, they are widely used to make radiators and heat sinks. If you open up your computer you can see that the heat sinks are most likely made from copper or aluminum.
Transition metals are also very good conductors of electricity. Copper and aluminum is widely used to make electrical wires.
Catalytic exhaust in an industrial building.
They are also used as catalysts. Catalysts are substance that can be added to a reaction to make it happen faster or to improve the yield of products or to make-sure an unfavorable reaction turns favorable. Catalysts are very important. For example the exhaust system in your car is also fitted with a catalytic converter. This converter make sure that the toxic gases and chemicals produced by the engine is converted into less toxic substances. They also used in factories to clean the toxic gases they produce. If not for these catalytic converters, the air we breathe will probably be very toxic. Iron, vanadium and nickle are examples of metal catalysts.