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 elements’ 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 it’s 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 Earth’s 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 Earth’s 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
today’s 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 don’t come in contact with oxygen. Iron is a good
example of this because it is used to make car bodies. If they didn’t 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 doesn’t 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 wouldn’t 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 Edition Molecules, 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