Properties of Transition Metals

Transition metal definition

Before we jump into the properties of transition metals, let’s first define what a transition metal actually is. For your exams, you need to know the following definition:

You might think that this definition means that all d-block elements are transition metals. However, that isn’t the case - they don’t all form stable ions with partially filled d-subshells. For example, scandium (Sc) and zinc (Zn) aren’t transition metals. To make life simpler for you, we’ve included a version of the periodic table that highlights the transition metals down below.

Fig. 1: The periodic table, shown with the blocks labelled and the transition metals highlighted in blue.StudySmarter Originals

Characteristic properties of transition metals

Now that we’ve got the definition of transition metals out of the way, we can move on to the main focus of this article: the properties of transition metals. We’ll look at their physical properties before considering their chemical properties.

We'll also pay particular attention to four characteristic properties that make transition metals act differently from other elements. These characteristic properties are:

• Variable oxidation states.
• Complex ion formation.
• Coloured ions.
• Catalytic activity.

But first up, let's explore the physical properties of transition metals.

Physical properties of transition metals

At earlier stages of your education, you probably learned some general properties of metals: they are hard, strong, and good conductors of heat and electricity. We can refer to these traits as a whole as metallic character. But when you look at metals in groups 1 and 2 in the periodic table, these properties don’t seem to hold. As we found out in the introduction, sodium (a group 1 metal) is soft, malleable, and reacts so vigorously with air and water that it must be stored in oil. This doesn't quite fit with 'metallic character!'

However, transition metals do live up to the stereotypical description of a metal - at least when it comes to their physical properties:

• Transition metals are hard and strong. We can also combine them in alloys to make them even stronger.

• They have high melting and boiling points.

• They are insoluble in water.

• In addition, they are good conductors of heat and electricity.

• Many transition metals are shiny and lustrous.

• They also have a high density.

Chemical properties of transition metals

Whilst you may already be familiar with the physical properties of transition metals, you might not have heard of some of their chemical properties. Some of these include their characteristic properties, which we'll discuss in more detail in just a second:

• Transition metals can have variable oxidation states.

• They also form complex ions.

• They produce coloured compounds and ions.

• In addition, they have good catalytic properties.

• Finally, transition metals don’t react much with water or oxygen.

Both the physical and chemical properties of transition metals help explain many of their common uses. We use gold in jewellery because of its shine and strength, and because it doesn’t react with the surrounding air. Brass (an alloy of copper) is strong, robust, and a good conductor of electricity, and so you find it in the pins in electrical plugs. Likewise, sturdy manhole covers are typically made from iron. Nickel is used as a catalyst to make margarine from oil, whilst blue cobalt ions contribute to the vibrant shades of certain paints.

As we mentioned earlier on in the article, the first four chemical properties in the list above (variable oxidation states, complex ion formation, coloured ions, and catalytic activity) make transition metals quite interesting. Although these particular properties aren’t unique to transition metals, they do make them stand out from the other elements! All four characteristic properties can be explained by the incomplete d-subshell found in transition metals. Let’s look at them in more detail.

Properties of transition metals: variable oxidation states

Transition metals show variable oxidation states. This means that they commonly lose different numbers of electrons in chemical reactions, and so take part in multiple types of redox reactions. For example, whilst sodium (a group 1 metal) is only ever found with an oxidation state of +1, the transition metal iron can have an oxidation state of +1, +2, or +3.

Properties of transition metals: complex ion formation

Do you remember what a dative covalent bond (also known as a coordinate bond) is? As the name suggests, it is a type of covalent bond, but in this bond, both shared electrons come from the same atom. The bond forms between a species with a lone pair of electrons and a species with a vacant electron orbital.

Well, transition metals tend to have multiple vacant and energetically accessible orbitals in their d-subshell. This makes them prime candidates for dative bonding! We call compounds containing transition metals bonded to other species with dative covalent bonds complex compounds.

Here are a few more terms you should know about when it comes to complex compounds:

• The transition metal ion within a complex compound is known as a complex.
• The bonded ions or neutral molecules are called ligands.
• Complex compounds can also be described by their coordination number, which is simply the number of coordinate bonds joined to the central transition metal ion.

Properties of transition metals: coloured ions

Have you ever wondered why crystals, such as emeralds and rubies, are so vibrantly coloured? We have transition metals to thank for that. Transition metal ions frequently form coloured ions, and their gorgeous hues are due to their partially filled d-subshells of electrons.

Here’s a brief explanation of transition metal colours:

• Transition metals have a partially filled d-subshell with five electron orbitals.

• These electron orbitals are divided into groups of different energy levels due to the presence of ligands. We call this splitting.

• The electrons in the transition metal’s d-subshell can move from a lower energy orbital to a higher energy orbital. As they jump to a higher energy level, they absorb energy in the form of visible light equal to the difference in energy between the two orbitals.

• The visible light spectrum is now missing certain wavelengths, which correspond to a certain colour. The colour we see is a combination of all the remaining wavelengths.

The same transition metal can have different colours, depending on factors like its oxidation state, type of ligand, and coordination number. For example, the green hue of emeralds and the deep red of rubies are both caused by trace amounts of the chromium(III) ion. However, the two vastly different colours are caused by the different groups bonded to chromium.

Fig. 3: A rainbow of transition metal ion colours.StudySmarter Originals

Properties of transition metals: catalytic activity

Finally, let’s look at the catalytic properties of transition metals.

You can see from the definition above why catalysts are so useful, particularly in the industry: they speed up chemical reactions without much of an additional cost. You only have to buy the catalyst once, and it could theoretically last forever!

Many transition elements and their compounds act as good catalysts. Here’s why:

• Transition metals show multiple different stable oxidation states and so can easily donate and receive electrons. This means that they act as good electron ‘storage sites’ during the chemical reaction.

• Many transition metals are good adsorbents. This means that reacting molecules can easily stick to their surface. Adsorption causes some sort of interaction between the reacting molecules and the surface of the transition metal, such as a weakening of the reactant’s bonds. This enables the reaction to take place.

Both of the two factors above help decrease the reaction’s activation energy and so increase the rate of reaction.