Transition metals are a group of elements that connect two parts of the periodic table. The word 'transition' comes from the Latin word transientum, meaning 'passing over'. These metals have atoms with a partially filled d-subshell, or form stable ions with partially filled d-subshells of electrons. In this article, we'll introduce you to transition metals in inorganic chemistry. We'll explore their location on the periodic table, general properties, and some of their applications. So, buckle up and let's dive into the world of transition metals!

What are transition metals?

Scientists sometimes disagree on their exact classification. In fact, there are a few different definitions. For your exams, you need to know the IUPAC definition we mentioned above. This includes most of the elements in the d-block of the periodic table. You can see this on the periodic table below. Here, the transition metals are highlighted in blue.

‍

It's important to note that not all elements in the d-block are transition metals, despite the term being used interchangeably. The reason for this will be discussed later on. Additionally, there are two other groups of elements called the lanthanides and actinides, with atomic numbers 57-71 and 89-103 respectively, which are sometimes referred to as inner transition metals. However, for this article, we will be focusing solely on the elements highlighted in blue above, as defined by IUPAC.

Transition metals in the periodic table

You can find the transition metals in the middle of the d-block section of the periodic table, which acts as a link between the s- and p-blocks. The highest energy subshell in the d-block is always a d-subshell. The transition metals can be found in groups 3-12 and periods 4-7, although what's more crucial is that they can be easily located in the periodic table.

Electron configuration of transition metals

We'll start with their electron configuration as atoms, and then look at how this changes as they form ions. This will also help explain why certain members of the d-block aren't classified as transition metals. This section probably won't make much sense if you haven't read Electron Shells and Electron Configuration. We'd recommend checking them out first to learn the basics of electron shells, sub-shells, orbitals, and filling rules.

Electron configuration of transition metal atoms

All transition metals can be found in the d-block of the periodic table, meaning that their valence electrons are located in a d-subshell.

It's important to remember that electrons are organized into shells and subshells, with four different types: s-, p-, d-, and f-subshells. An element's position in the periodic table indicates the highest energy subshell where its electrons are found. For instance, the highest energy subshell for p-block elements is a p-subshell. As we move across the period in the periodic table, each transition metal has one more electron than the previous one. These electrons fill up the d-subshell gradually, although there are some exceptions. To illustrate this, let's take a closer look at the first row of transition metals (period 4) and highlight it below.

‍

Let's take a look at their electron configurations. As in the periodic table, we've highlighted the transition metals.

‍

The first two elements in period 4, potassium (K) and calcium (Ca), are located in the s-block of the periodic table. The valence electrons of these elements are found in the 4s-subshell, and their 3d-subshells are empty.

Subshells typically fill up in a specific order, from the lowest to the highest energy level, which typically follows the pattern of lowest to highest numbers. However, 3d-subshells are an exception to this rule since they have slightly higher energy levels than 4s-subshells. As a result, the 3d-subshells fill up after the 4s-subshells, which is another tricky exception to the filling pattern that you need to remember.

The next ten elements in the period belong to the d-block, and their electrons are added to the inner 3d-subshell one by one as we move across the period. For example, scandium (Sc) has 21 electrons and just one electron in its 3d-subshell, resulting in an electron configuration of [Ar] 3d1 4s2. On the other hand, titanium has 22 electrons and two electrons in its 3d-subshell, resulting in an electron configuration of [Ar] 3d2 4s2.

However, the filling pattern is interrupted by two elements, chromium (Cr) and copper (Cu), both of which have partially filled 4s-subshells. This is due to the fact that the 4s- and 3d-subshells have very similar energy levels. Since the unpaired electron in the 4s-subshell does not experience any electron-electron repulsion, its energy level is lowered, which more than compensates for the additional electron in the slightly higher energy 3d-subshell. Electrons always prefer to occupy the lowest energy state possible. Additionally, having a half-full 3d-subshell, as in the case of chromium, or a completely filled 3d-subshell, as in the case of copper, helps stabilize the atom.

‍

‍

Electron configuration of transition metal ions

All transition metals form positive cations by losing electrons.

You might remember from Electron Configuration that although the 3d-subshell is of a slightly higher energy level than the 4s-subshell, atoms lose electrons from the 4s-subshell first. This means that all transition metals lost their 4s electrons before their 3d electrons.

Take iron (Fe) as an example. It commonly forms ions with charges of 2+ or 3+. Iron has the electron configuration of [Ar] 3d6 4s2. When forming a 2+ ion, it first loses its 4s electrons, giving it the electron configuration of [Ar] 3d6 4s0. To form a 3+ ion, it needs to lose a further electron. Since the 4s-subshell is now empty, this electron is lost from the 3d-subshell, giving the ion the electron configuration of [Ar] 3d5 4s0.

‍

Why aren't all of the d-block elements transition metals? This is because they don't all form stable ions with incomplete d-subshells. For example, scandium (Sc) only forms 3+ ions in all of its compounds, which gives it the electron configuration of [Ar] 3d0 4s0. Its 3d-subshell is completely empty, so it isn't a transition metal. Likewise, zinc (Zn) only forms 2+ ions in all of its compounds. These ions have the electron configuration of [Ar] 3d10 4s0. Its 3d-subshell is completely full, so it isn't a transition metal.

Properties of transition metals

Transition metals all have similar properties. They are good conductors of heat and electricity, are hard and strong, and have high melting and boiling points. Compared to group 1 and 2 metals, they are also relatively unreactive. This makes them extremely useful, but we'll explore that in the next section. For now, let's look at some of their other characteristic properties. There are four in particular that you need to know about when it comes to transition metals: We explore these properties in much more depth in Properties of Transition Metals.

Uses of transition metals

Transition metals have a wide range of uses due to their desirable properties. Aluminium, for example, is lightweight and non-toxic, making it useful in the production of car and aircraft parts, as well as in the manufacture of cans and foil for food packaging. Iron, on the other hand, is strong and inexpensive, making it ideal for use in building materials, such as bridges, ships, and structural frameworks. It also accounts for a significant portion of the world's metal production.

Copper, with its excellent electrical conductivity, is used in electrical wires. Titanium, in the form of powdered particles, is used in the pyrotechnics industry to create brightly-burning particles in fireworks. Tungsten is used in light bulb filaments and X-ray tubes. Transition metals often form alloys, which are compounds made from mixtures of elements, at least one of which is a metal. Alloys are generally stronger than pure metals because they contain different-sized metal ions that distort the metal lattice, making it harder for ions to slide over each other. Some useful transition metal alloys include brass (made from copper and zinc), steel (made from iron and carbon), and sterling silver (made from silver and another metal, usually copper).

Yes, those are all key takeaways about transition metals. It's important to understand their unique properties and characteristics in order to fully appreciate their various applications and uses in different industries. Their ability to form alloys and complex ions, as well as their catalytic properties, make them incredibly versatile and valuable in a wide range of settings.

Transition Metals

Why are transition metals good catalysts?

Transition metals are good catalysts as they can change their oxidation state, and they have the ability to adsorb other substances.

Are transition metals reactive?

Transition metals are less reactive than other groups due to high ionization energy and high melting point.

Which metals are transition metals? 

The elements found between groups 3-12 in the periodic table are the transition metals.

Explain why Sc and Zn are not classified as transition metals.

They do not have a partially filled d-subshell in their atomic state or their common oxidation state (i.e., Zn2+, Sc3+), hence they are not regarded as transition elements.

What are transition metals and where are they found on the periodic table?

Transition metals are metals whose atoms have a partially filled d-subshell, or which form at least one stable ion with a partially filled d-subshell of electrons. They are found between groups 3-12 on the periodic table.

‍