Video Transcript
In this video, we will learn about
the transition metals, some of their uses and their chemical and physical
properties.
Before we look at this very
interesting collection of elements, it’s important to know which are and are not
included. The term transition metal is about
100 years old. It originally meant any element
that sits between groups one and two and groups 13 to 18. These elements provided a
transition between the two blocks, although it should be noted that not all of these
elements had been discovered at the time. Today, this definition would
include all of the d block elements and all of the f block elements as well.
However, over time, certain
properties of this collection of elements have become signatures and certain
elements were removed. For some elements, there is
disagreement over whether they should be called transition elements. I won’t go into the details of
these disagreements, but I will show you which elements are generally considered
transition elements.
The definition from the
International Union of Pure and Applied Chemistry, IUPAC, includes these
elements. Almost universally, zinc is not
included. The status of cadmium and mercury
is hotly debated. And for some of the heavier
elements, there hasn’t been enough experimental data to make a clear decision. But in practice, elements in group
12 of the periodic table are not considered transition elements.
At the other end, some people don’t
consider group three elements transition elements, either. This includes scandium and
yttrium. To keep things simple in this
video, these are the elements we will consider to be transition elements or
transition metals. This means we’re including any
element in group three to 11 plus any element in the f block.
Another thing that happens in
practice is that transition metal generally referred to only those transition metals
in groups three to 12. And those in the f block are
specifically referred to as the inner transition metals. Meaning that what we’re left with
when we talk about transition metals or elements are the elements in groups three to
11. This is the collection of elements
we’ll be considering in the rest of this video. We won’t be looking at the reasons
for the properties, just the properties themselves.
Next up, the physical properties of
the transition metals. Like other metals in their pure
form, transition metals are thermally and electrically conductive. However, the three most conductive
metals of all are all transition metals: gold, copper, and silver, with silver being
twice as conductive as aluminum. The transition metals are also
generally quite hard, at least harder than the main group elements like tin and
lead.
Some of them are also very strong
like iron and titanium. The mass of one cubic centimeter of
water is about one gram, so water has a density of one gram per cubic
centimeter. The element lead in metallic form
is generally considered to be pretty dense, being 11 times denser than water. But the densest of all the elements
are osmium and iridium, which are 23 times as dense as water and twice as dense as
lead. And there are actually 10 more
transition metals in the d block that are denser than lead.
Like many other metals, transition
metals tend to be malleable and could be hammered or rolled into various shapes. And they’re ductile, so they can be
drawn into thin wires. And they’re shiny, like other
metals, or lustrous and could be polished to a mirror finish. Last of all, transition metals tend
to have high melting points. Lead in group 14 has a melting
point of about 328 degrees Celsius. But the metal that has the highest
melting point of all the metals is tungsten, a transition metal.
Now that we’ve looked at the
physical properties of the transition elements in their metallic form, let’s have a
look at their chemistry. One of the most important
distinguishing features of transition elements is the number of compounds they can
form. A lot of this has to do with the
fact that they can form different stable ions and oxidation states. Main group metals, like magnesium
and aluminum, tend to have only one common oxidation state. Magnesium tends to form Mg2+ ions,
while aluminum tends to form Al3+ ions. But we can see many other stable
oxidation states for some of the transition metals.
Here, we’re going to go through the
first row of the d block. Scandium is an exception in that we
only tend to see it in the plus three oxidation state, neglecting zero, of
course. The other transition elements along
this row have multiple common oxidation states. For reference, zinc at the end of
this line of the d block has only one common oxidation state, plus two. It is important, however, to
remember that sometimes we can get different oxidation states than these. These represent the common
oxidation states, and some people disagree about exactly what common is. Therefore, you should only take
these numbers as guidance.
When we find transition elements in
low oxidation states, we’ll typically see them as ions, whereas the higher oxidation
states, we’ll typically see as oxides or fluorides and so forth. As an example, we can see the great
variety of compounds possible with manganese with all these possible oxidation
states. The ability to easily switch
between these available oxidation states allows for a huge range of catalytic and
electrochemical behavior.
The other striking feature of
transition elements is the variety of colors of their compounds. If we look at the color, we can
predict what frequencies of light the ion is absorbing. For instance, an ion that absorbs
red light looks green. Ions of zinc, magnesium, and
aluminum have no color whatsoever. Scandium three plus is also
colorless. But solutions of titanium three
plus are purple. There’s quite a variety of vanadium
ions or vanadium oxide ions with color. Solutions of V2+ are a violet
purple, while solutions of V3+ are green. Solutions of VO2+ are blue, and
solutions of VO3+ are yellow. Solutions of chromium three plus
are also a violet purple.
Manganese can form a huge variety
of colored compounds, but I’m only going to include those you probably come across
in solution. The Mn2+ ion makes solutions a pale
pink, while solutions of the permanganate ion, MnO4−, are an intense purple. The most common ions of iron are
Fe2+ and Fe3+. You may see the colors of Fe2+ and
Fe3+ quoted differently because it does change depending on the environment. But generally speaking, Fe2+
solutions are green, while solutions of Fe3+ are yellow or brown. Solutions of cobalt two plus ions
are generally pink, but they can turn blue if extra Cl− is added. Meanwhile, solutions of nickel two
plus are green, and solutions of copper two plus are generally blue.
These colors are not exact. The counterion and the environment,
the temperature, and so forth can affect the color of a transition element ion
solution. However, in certain controlled
environments, the color can be so distinctive we can use it to identify the ion.
Now, we can move on to one of the
more unfortunate properties of some of the transition metals: toxicity. Before going any further, it’s
vital to point out that toxicity depends on the form of the element, whether it’s
pure form or whether it’s in some kind of compound. Some of the transition metals form
compounds that do vital jobs in plants and animals. But for some of the transition
elements like vanadium, chromium, and cobalt, very many of the compounds are highly
toxic. But as with many materials, many of
the transition elements in high doses will be toxic, including those that are vital
for biological functions.
The last significant property of
the transition elements we need to look at is reactivity. In their pure form, none of the
transition metals are highly reactive. And in fact, the least reactive
metals of all are all transition metals. Silver is quite unreactive but will
tarnish. Gold, however, is considered to be
the least reactive metal of all. A good test of reactivity is how a
metal responds to acid. Copper is more reactive than gold
and silver, but it will not react with acids on their own, so it’s considered
relatively unreactive. But the majority of transition
metals do react with acids.
Also, most of the transition metals
will react with oxygen forming transition metal oxides, although some, like copper,
need to be heated first, to get a decent reaction rate. On the other hand, the transition
metals generally at room temperature will not react with water. The process of iron rusting is a
separate type of process. But with enough heat, some of the
transition metals will react with hot water or steam.
In compound form, the transition
elements can be oxidized and reduced, switching between those available oxidation
states. For instance, we can oxidize Fe3+
to Fe2+ or reduce Fe2+ to Fe3+, switching between green and yellow slash brown forms
of iron ions.
This behavior is partly what
contributes to transition elements and transition element compounds being fabulous
catalysts. For instance, iron is used in the
Haber process to convert nitrogen and hydrogen gases into ammonia, and vanadium five
oxide is used as a catalyst in one of the steps of the contact process, helping to
convert SO2 into SO3. And there are many biological
molecules that depend on transition metal ions in order to function like enzymes and
proteins.
But it’s all very well looking at
these things in isolation, but we’ll get a better idea of how transition metals fit
into the greater picture by comparing them. Let’s compare the first transition
series, the top row of the transition metals, with the group one and group two
metals in the same period. And I’ll also throw in zinc.
All these elements in their pure
form are lustrous. And most are silvery, and copper is
an orange brown. All of these transition metals and
zinc are relatively hard, but potassium and calcium are quite soft. Something really interesting pops
out when we look at the melting points. Here, I’m presenting them in
kelvin.
Potassium has a relatively low
melting point at only 337 kelvin. Calcium’s seems much higher. Potassium’s melting point is only
64 degrees Celsius. But the melting point for all these
transition elements are all substantially above 1300 degrees kelvin. And we see the melting point drop
down again at zinc, with a melting point of only 693 kelvin.
The differences between the alkali
and alkaline Earth metals become even more dramatic when we look at their chemical
properties. When potassium or calcium are added
to cold water, we see fast almost explosive reactions. However, none of the transition
metals or zinc react directly with cold water. The rusting of iron is a separate
process.
Meanwhile, pure calcium and
potassium will react fast with oxygen tarnishing in air. But for the rest of the elements,
the reaction is slow and generally requires heat. But the most dramatic difference
occurs when we use acid. Potassium and calcium explode,
while the transition metals have slow reactions or nothing at all in the case of
copper.
And if we look at the number of
common oxidation states, the average for the transition metals is significantly
higher for the alkali or alkaline Earth metals. And we can also see that the alkali
and alkaline Earth metals are significantly more reactive overall than the
transition metals. After all that, I think it’s time
for some practice.
Which of the following is not a
transition metal? (A) Gold, (B) cobalt, (C)
potassium, (D) rhodium, or (E) zirconium.
Transition metals are otherwise
known as transition elements. And where do we find elements? On the periodic table. The periodic table of elements
condenses lots of different bits of information about the elements, so we can see it
all collectively. The elements inside the green area
are generally known as transition metals. And the ones most people talk about
are in groups three to 11 of the periodic table.
Now, let’s see which of the
elements listed actually lie inside the area. If you look carefully, you’ll find
the entry for gold in group 11 and period six. The symbol for gold is Au. Cobalt, with simple Co, can be
found in group nine and period four. Potassium, with symbol K, is also
in period four, but it’s in group one. Rhodium, symbol Rh, is found below
cobalt in group nine and in period five. And lastly, zirconium can be found
in group four and period five.
We can clear away the f block
because none of the elements are inside it. The only element that’s not inside
the area is potassium. It is not a transition metal. Potassium is, in fact, reactive,
soft, and an alkali metal. Therefore, out of the five
elements, the only one that’s not a transition metal is potassium.
Now, let’s have a look at the key
points. Transition metals or elements are
found in the d block and f block of the periodic table. Those in the f block are generally
known as inner transition metals and won’t be included when we talk generally about
transition metals. Like many other metals, transition
metals are electrically and thermally conductive and lustrous or shiny in their pure
form. They are also strong and hard,
malleable and ductile, with high melting points. They tend to form colored compounds
and commonly have multiple common oxidation states, which is part of why they can be
very good catalysts. They are also less reactive than
alkali and alkaline Earth metals, and the least reactive of all metals are
transition metals.
