We just finished our survey of the main group elements, which are found in the s and p-blocks,
so now it’s time to head into less familiar territory. The d-block, which contains Groups 3
through 12, are elements whose outermost electrons are d electrons. We should remember what d
orbitals look like from general chemistry, and because there are five per energy level,
the d-block is ten elements across. Due to their partially filled d subshells, these elements are
also called the transition metals, although Group 12 itself technically does not qualify
for this term since elements in this group do have a completely full d subshell. Now the tricky thing
about transition metals is that their properties are not as predictable as the elements in the s
and p-blocks. Most transition metals exhibit a variety of oxidation states, and they have
fascinating bonding behaviors, as we will learn progressively throughout this series. But these
elements have an enormous range of applications, beyond their utility in organometallic chemistry
which will be our primary focus, so let’s talk a bit about these elements right now.
One thing to keep in mind is that because of the shapes and relative energies of the different
orbitals, each period has a d subshell that is one behind its s and p subshells in terms of principal
quantum number. So the transition metals in the fourth period are filling their 3d subshell.
Those in the fifth period are filling their 4d subshell, and so forth. Let’s start by looking
at this first row of the d-block. From left to right we have scandium, titanium, vanadium,
chromium, manganese, iron, cobalt, nickel, copper, and zinc. Most of
these should be relatively familiar, whether from their common use in everyday materials,
or from compounds we learned about in organic chemistry, while a few might be unfamiliar.
Scandium is used in aluminum alloys for aerospace components. Titanium is an important
metal for manufacturing lightweight yet durable products, from bicycle frames to artificial hips.
Vanadium is used to make steel alloys. Chromium is used as a protective plating on plumbing fixtures
and automotive detailing. Manganese should be familiar from oxidizing agents like potassium
permanganate. It is also used to make glass, as a pigment, and as filler in dry cell batteries.
Iron is absolutely everywhere, from the cutlery in your kitchen, to cars, planes, and skyscrapers.
It’s even in the hemoglobin in your blood. Cobalt is used in machinery and electronics.
Nickel is found in useful alloys and is an important component of many batteries. It is also
used to make coins. Copper is tremendously useful for making wires and other electrical equipment,
as well as pipes and tubes. And zinc is frequently used to galvanize other metals to prevent rusting.
It is also used in sunscreens and cosmetics, and is essential to human health.
Moving on to the next row, we have yttrium, zirconium, niobium,
molybdenum, technetium, ruthenium, rhodium, palladium, silver, and cadmium. Yttrium is
found in aluminum and magnesium alloys. Zirconium oxide is used to make highly durable ceramics,
as well as imitation diamonds. Niobium is used in various alloys and superconducting materials.
Molybdenum is used to make steel alloys as well as lubricants and pigments. Technetium has an
isotope that is metastable and emits gamma rays that give it utility in medical imaging.
Ruthenium oxide is used to coat electrodes. Rhodium is used in catalytic converters for cars,
as is palladium. Silver is used to make jewelry and silverware,
coins, as well as mirrors, being that it is the best reflector of visible light we know of. And
cadmium is widely used in rechargeable batteries, as well as control rods for nuclear reactors.
Arriving now at the third row in this block, we find lutetium, hafnium, tantalum,
tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. Lutetium oxide is used to make
catalysts in the petrochemical industry, and lutetium-hafnium dating is used for determining
the age of meteorites, due to the long half-life of lutetium-176. Hafnium resists corrosion and
is used to make wires. Tantalum is also used to make wires, and is present in various alloys.
Tungsten is widely used in heating filaments, as well as electrodes, and is present in many
useful alloys. It has the highest tensile strength and melting point of any element.
Rhenium and osmium are primarily used in alloys. Iridium is used as a hardening agent for platinum,
which is used in jewelry, electrodes, and other laboratory instruments.
Gold is famous for its monetary value, and is used in jewelry for this reason,
but is also important in dentistry and certain computer components. And mercury has long been
used in thermometers, barometers, and other scientific instruments, although due to its
toxicity, was eventually disfavored for other substances. As we already learned,
mercury is one of only two elements, along with bromine, that is liquid at room temperature.
And finally, the fourth row in the block, which is part of period seven, includes lawrencium,
rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, darmstadtium,
roentgenium, and copernicium. None of these elements occur naturally and are exclusively
synthesized in particle accelerators, with only a few atoms having ever been made for most of these
elements. They are all highly radioactive, and have no application beyond scientific research.
So what are some of the properties of transition metals? Most of them are hard, high-melting solids
that conduct heat and electricity very well. One important thing to discuss is the common
oxidation states of these elements. Here is a table illustrating the common oxidation states
for the first row of the d-block. As we can see, some elements like scandium and zinc have only one
oxidation state, whereas manganese has five, and in fact the number of possible oxidation states
increases moving to the middle of the table, and then decreases to the end, apart from copper,
which has at least four oxidation states. This is because on the left side, the oxidation states
are limited by the number of electrons in the 4s and 3d subshells. Moving down to other periods,
higher oxidation states become more and more common for reasons of increasing atomic radius.
In terms of isolating these metals, some of them have a very long history,
as iron, copper, silver, and gold have been known for most of human civilization. In fact,
we demarcate certain periods in human history as the bronze age and iron age, to indicate when we
became able to isolate certain metals and use them to make tools, weapons, and other things.
Most of the other transition metals are extracted from various ores, which present
a range of difficulty, depending on the metal’s concentration, what else is present in the ore,
and ease of reduction to the neutral metal. But as the goal of this series is less of a focus on
metallurgy and more on organometallic catalysis, we will not discuss the details of this process
for each individual metal. Instead we just want to get a general sense of their properties,
as certain metals will come up again and again as we learn about different reagents and catalysts.
With the d-block covered, there is just one section of the periodic table left,
and that’s the f-block. This is always found hovering mysteriously below the rest of the table,
and this is for very good reason. If the periodic table were to be displayed intact,
the f-block would occur immediately after the s-block, in periods six and seven. So that would
look like this, with the s, f, d, and p-blocks in this order, so that there is no interruption in
the increase of atomic number when moving left to right. The only thing is that scandium and yttrium
should actually shift over to sit above lanthanum and actinium because they have similar electron
configurations, ending in d1. This may seem a bit confusing, but it is only after one d
electron is present that the f subshell begins to get filled, so the rest of the f-block comes next,
and then only once we get to this column with hafnium and rutherfordium do elements begin
adding d electrons again, even though the d-block technically begins one group sooner.
At any rate, since there are 7 f orbitals per energy level, the f-block is 14 elements long,
and because we almost never have to discuss any of these incredibly rare elements,
except for maybe uranium from time to time, it is much more convenient to snip
this region out and condense the rest, to make it more manageable. But it is very important to know
that this is where the f-block would go if all the elements were to be displayed continuously.
Much like with the d-block, because of the shapes and relative energies of the orbitals,
the f subshell for a given period will be two behind the s and p subshells,
and one behind the d subshell, in terms of principal quantum number. So period 6 goes 6s,
then 4f, then 5d, then 6p, while period 7 goes 7s, then 5f, then 6d, then 7p. This is strictly
due to the Aufbau principle, which dictates the order in which orbitals will be filled.
Let’s quickly go through and name these elements as well. The first row in the
f-block is called the lanthanides. This is because the first element in this row is called
lanthanum. After that we have cerium, praseodymium, neodymium, promethium, samarium,
europium, gadolinium, terbium, dysprosium, holmium, erbium, thullium, and ytterbium.
The lanthanides are still small and stable enough for some of them to have practical applications,
primarily in alloys. But additionally, neodymium glass is used to make lasers, and others are
used in control rods for nuclear reactors. Then finally, the second row in the f-block
is called the actinides, because the first element in this row is called actinium.
After that we have thorium, protactinium, uranium, neptunium, plutonium, americium,
curium, berkelium, californium, einsteinium, fermium, mendelevium, and nobelium. These elements
are very heavy and most are extremely radioactive, but some still have utility. Thorium oxide is used
in a number of materials, curium is used as a fuel for radioisotope thermal generators,
and of course we all know of the usage of uranium and plutonium in nuclear reactors and weapons.
And with that, we conclude our survey of the periodic table. These are all of the elements
that exist, everywhere in the universe, with precisely the properties we discussed,
no matter where we find them. There are those who would protest such a definitive statement,
but they would do well to learn basic principles of chemistry and physics,
as we have together on this channel, so that they could grasp this simple yet powerful
concept. Starting with one proton in the nucleus for hydrogen, and going through every integer
value all the way up to the largest nuclei that exist for mere fractions of a second,
if any alien civilization out there has synthesized elements beyond what we call
oganesson, with its 118 protons, they must cope with their extreme instability just as we will,
if we ever do the same. Hopefully this construct now seems a little less daunting,
and the nature of the chemical elements feels a bit more predictable. With this basic information
now out of the way, it’s time to learn a lot more about transition metals and what they can do.