The f-block elements belong to the inner transition element category. In particular, they belong to the two series – lanthanoids or 4f series, and actinoids or 5f series. Lanthanoids and actinoids have a specific placement in the periodic table due to their electron configurations. This is the reason they belong to the inner transition element category. This article has tried to look at specific properties of f-block elements in both series.

Properties of f-block Elements

• f-block elements are complex and heavy metals.
• They have high melting and boiling points.
• The f-block elements exhibit varying oxidation states.
• They form coloured ions.
• f-block elements may likely form complex compounds.
• The unique properties of f-block elements are the reactivity of actinides.
• f-block parts also have magnetic properties.
• When the atomic number of the f-block elements increases, their atomic size decreases.
• Furthermore, their electrons fill the (n-2)f orbitals.
• One of the essential properties of f-block elements is that they are highly electropositive. They are also highly reactive.

Now that we have an overview of the properties of f-block elements, let us understand them in detail by studying the properties of the two series of f-block elements. As mentioned above, these two series are- lanthanoids and actinoids.

Properties of f-block Elements (Lanthanide Series)

Electronic configuration

All tripositive ions of the lanthanoid series have an electronic configuration of 4fn. Here, n can be from number 1 to 14. Also, tri-positive ions have the most stable oxidation state compared to other lanthanides.

Atomic sizes, Ionic sizes

The unique feature of the lanthanoid series is the decrease in their atomic and ionic sizes. This property of f-block elements is called lanthanoid contraction. There is a remarkable decrease in size when the atomic number increases. Moreover, due to lanthanoid contraction, Zr and Hf occur together in nature. Therefore, it becomes difficult to separate them from each other.

Oxidation state

La(II) and Ln(III) are more dominant in the lanthanide series than others. However, +2 and +4 ions are also present but less frequently. They are often present in solid and liquid solutions.

General Characteristics of Lanthanides

Below are some general properties of f-block elements of lanthanide:

• Lanthanides are all silvery-white substances. They are soft metals and tarnish very quickly.
• All lanthanides have a typical metallic structure. Hence, they are also good conductors. They conduct both electricity and heat. 
• The density keeps changing slightly along with the series.
• Many trivalent ions of the lanthanoid series form coloured ions. These coloured ions are present in aqueous solutions.

Properties of f-block Elements (Actinide Series)

This series of f-block elements have fourteen elements in them. These range from Th to Lr. The unique property of the actinide series is its radioactive nature.

Electronics configuration

The electronic configuration of actinide elements is 7s2. They also have variable occupancy and can be of 5f and 6d subshells. There are irregularities in the actinoid’s electronic configuration. These irregularities are similar to lanthanoid abnormalities.

Ionic sizes

The ionic radii of actinides decrease with an increase in the atomic number of actinoids as we move across the series in a periodic table. This property of actinide is called actinoid contraction.

Oxidation states

As 5d, 6f and 7s have comparable energies, there is an excellent range of oxidation states in the actinide series. The properties of f-block elements of actinide series generally consist of a +3 oxidation state. Moreover, a higher oxidation state is present in elements of the first half of the series.

General Characteristics of Actinides

• The appearance of actinoids is silvery. However, they have variety in their structures.
• They have irregular metallic radii.
• They are highly reactive.
• They have more complex magnetic properties as compared to lanthanides.

Conclusion

The properties of f-block elements are present and can be studied in two series. These series are lanthanoid and actinoid. The primary feature of f-block elements is the way they contract. These contractions are namely- lanthanoid contraction and actinoid contraction. f-block elements are heavy metals with high melting and boiling points, and they tend to form coloured ions and complex compounds. In addition, the oxidation states of f-block elements are variable.