A Level Chemistry Revision: Inorganic Chemistry – Transition Metals

The transition metals, or transition elements, are those belonging to groups 3 to 12 in the periodic table, with the exception of the lanthanides and actinides, which have their own periodicity properties.

Unlike other elements, the transition metals have more complex behaviours in terms of their electron configurations, and are relatively more difficult to figure out.

Many electron configurations are straightforward and simple to understand. You can easily make predictions about their relative reactivities with other elements. You can also easily see what types of bonds they’re going to form with certain elements by simply looking at the outer shell and analysing how they’re going to gain or lose electrons in chemical reactions.

The electron configurations of transition elements, on the other hand, are much harder to analyse.

They behave in a more complex way when they interact with other elements and compounds. Continue reading to learn about their electron configuration pattern and what properties transition metals have.

What Defines the Transition Elements?

With the exception of the lanthanides and actinides, transition elements belong to groups 3 to 12 in the periodic table.

They all have metallic properties, which is why they’re also known as transition metals. Groups 3-12 are also classified as d-block elements because their subshell has the highest energy level, a d-subshell.

Diagram of the periodic table

The metallic properties of transition elements include high boiling points and electric conductivity. However, they’re not as reactive as the metals in groups 1 and 2. Some of the metals that belong to the transition elements are non-reactive and relatively rare. The more familiar ones, like silver, gold, and platinum, are also very valuable.

The compounds formed by the transition metals are distinctive because of their wide range of vivid colours. For example, the transition metal compounds that are soluble in water produce bright colours. This happens because the visible light of the spectrum that passes through the dissolved particles is absorbed by the d-orbitals at various energy levels. The unabsorbed light waves are the ones that produce the colours in the solutions.

Here are some examples of transition metal compounds that produce distinctive colours when dissolved in water:

  • Cobalt(II) nitrate – reddish colour
  • Potassium dichromate – orange
  • Potassium chromate – yellow
  • Nickel(II) chloride – blue-green colour (cyan)
  • Copper(II) sulphate – marine blue
  • Potassium permanganate – purple (magenta)

What is the Electron Configuration Pattern of the Transition Metals?

Transition elements belong to the d-block because their subshell has the highest energy level, which is a d-subshell. From there, you can see why the elements behave differently.

Some elements, like gold, have a completely filled d-subshell. Gold’s electron configuration can be written as [Xe] 4f14 5d10 6s1. This makes it unreactive and stable. The d-subshell can hold a maximum of 10 electrons.

When revising the transition metals in A level chemistry, you only need to be familiar with the electron configurations of the 10 elements of the first row of the d-block elements. Each of these elements represent a group of elements that has very similar properties.

You can easily write the electron configuration by just adding one electron onto the 3d subshells. You start with scandium, with the electron configuration of:

1s22s22p63s23p64s23d1

You then end with zinc, which has a completely filled 3d subshell:

1s22s22p63s23p64s23d10

But there are two exceptions to this pattern: copper and chromium. Copper has an electron configuration of 1s22s22p63s23p64s13d5 while chromium has an electron configuration of 1s22s22p63s23p64s13d10.

As you can see, the 4s-subshell before the 3d-subshell is only half-filled. In these elements, the lower energy orbitals are only half filled to favour the complete filling of the higher energy orbitals.

What Are the Properties of the Transition Metals?

Just like other elements, the transition metals exhibit periodicity from left to right. Generally speaking, this means their physical and chemical properties gradually change as you move from left to right.

The electrons in the outer shells of the atoms of the second and third rows of elements have weak shielding effects. This results in an increase in effective nuclear charge, because the number of protons is increasing.

As a result of weak atomic shielding and strong effective nuclear charge, the following trends can be observed as you go across the row from left to right for the second and third rows of elements:

  • Atomic radius decreases
  • Ionisation energy increases
  • Electronegativity increases
  • Elements become less metallic

This trend continues until you reach calcium under group 2, or the alkaline earth metals. An abrupt break in the trends is exhibited by the first transition series. These elements have very similar physical and chemical properties, which is why we can classify them as a group. The similarities of these elements are partly explained by the fact that they have relatively small differences in their effective nuclear charge.

Some of the properties that are common among the transition metals are:

  • Large ratio between the charge and the radius of the atoms
  • The elements have high densities and are hard
  • They have high melting and boiling points compared to other metals
  • Many of the compounds that they form are commonly paramagnetic
  • The elements have varying oxidation states
  • Brightly coloured compounds and solutions are formed by the elements
  • Their compounds have strong catalytic properties
  • They form stable complexes

What Are the Catalytic Uses of the Transition Metals?

The transition metals are excellent catalysts for various important chemical reactions. The surfaces of the transition metals can serve as reaction sites. The reactants can be adsorbed onto them then later desorbed after the reactions. They can also change their oxidation states to form bonds with the reactants, providing lower activation energy for reactions to occur.

Some of the important catalytic actions of the transition metals are:

  • Iron: Used in the Haber process to produce ammonia on an industrial scale.
  • Vanadium oxide: This is used as a catalyst to produce sulphur trioxide and sulphuric acid.
  • Nickel: This is very useful in the hydrogenation of alkenes, breaking their bonds to form alkanes.

For more A level chemistry resources to help you revise and for information on studying chemistry A level, check out our A Level Chemistry Resources hub.

Original post: A Level Chemistry Revision: Inorganic Chemistry – Transition Metals. No Republication or Redistribution allowed without written consent. Contact ReAgent Chemicals for more information.

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