The Importance of d-block Transition Metals

By: Daniel Bates

 

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 elementsí 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. For more common knowledge on transition metals check out http://www.chemicalelements.com/groups/transition.html

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 itís 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 Earthís 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 Earthís crust: hematite Fe2 O3 and magnetite Fe3 O4. The ore is put into a blast furnace with some coke and limestone. The 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 todayís 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 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 donít come in contact with oxygen. Iron is a good example of this because it is used to make car bodies. If they didnít 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 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 to paramagnetism 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 cells used to convert solar energy into heat energy and eventually it is converted into electrical energy. For more on solar energy check out http://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 doesnít 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 wouldnít 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 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 in order of importance:

1.      Chemistry 4th EditionMolecules, 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