f- Block Element as an Inner Transition Element

f- block elements are the elements in which the last electron will enter into the f orbital, members of the third group. They are divided into two groups named lanthanides and actinides. They are placed at the bottom of the periodic table.

Due to their placement and electronic configuration f, block elements are known as inner transition elements.

In f- block elements, the last electrons or valence electrons generally enter into (n-2)f orbitals that are inner to transition elements (n-1)d, known as internal transition elements. Their electronic configuration is (n-2)f¹⁻¹⁴, (n-1)d⁰⁻¹,ns²

f-block elements as inner transition elements

f-block elements are the elements in which the valence shell electrons are filled in an f subshell.

They are divided into two subclass

•       Lanthanide -most the lanthanides are colourless,

The differentiating electron or valence electron enters into the 4f subshell, also known as rare earth. The binding energy of 4f is higher.

•       Actinoid – most are coloured, and the differentiating electrons enter into a 5f subshell. The binding energy of 5f is lower.

Lanthanide

        Electronic configuration – [Xe] 4f¹⁻¹⁴ 5dº⁻¹ 6s²

•       They are rare earth elements found naturally on earth. Lanthanide includes a total of 14 pieces ranging from atomic no. 57 (cerium) to 71( Lutetium ). Every aspect is radioactive except promethium as
•       Their melting and boiling points are higher than other elements, but they don’t follow common trends.
•       Lanthanides have coloured ions because of unpaired electrons.
•       They do not have higher ionisation energy because of their large size than alkaline earth metals.
•       Lanthanides are very reactive because of their low ionisation energy.
•       They have a large ion size, and due to this, they have a minimal tendency to form complex coordination compounds.
•       Lanthanides’ most common oxidation state is +3, but some also have +2 and +4 oxidation states. They act as a very good reducing and oxidising agent by losing and gaining electrons.
•       Lanthanide contraction is the gradual decrease in the atomic and ionic radius of lanthanide elements with an increase in nuclear number.

Reason for lanthanide contraction

When we go up in the lanthanide series, there is an addition of electrons at each level. Also, there is an increase in nuclear charge at each level, increasing attraction between the nuclear and the outermost shell at each step.

But the shielding effect of 4f electrons is inferior because of the shape of their orbitals, so they cannot shield the attracting force of the nucleus. The 4f electrons are unable to cover the inward pull of the nucleus.

This results in an increased nuclear attraction between the nucleus and outermost electrons which becomes the reason for the small size of ionic and atomic radius.

Actinoid

            Electronic configuration – [Rn]5f¹⁻¹⁴ 6d⁰⁻¹ 7s²

•       This series consists of 14 elements ranging from atomic no 89( actinium) to 103 (lawrencium).
•       They don’t occur naturally on earth. They are artificial elements, and they are also known as transuranic elements, which occur beyond uranium with an atomic number between 92 and 103.
•       The valence electron in actinides enters into a 5f orbital.
•       The common oxidation state exhibited by these elements is +3, but they can also show +7.
•       Actinoid contraction is almost similar to lanthanide contraction because of the poor shielding effect of 5f electrons.
•       They have higher melting and melting points.
•       Actinoids also form coloured ions.
•       Actinides are radioactive. Because of this nature, they are used to make nuclear weapons and used in nuclear reactors.
•       They release hydrogen when they react with boiling water or dilute acid.

2Ln + 6HX → 2LnX3 + 3H2

Characteristics of inner transition elements

•       They form coloured ions as well as tend to create a complex of coordination compounds too. Example [Ti(H20)6]+3

•       They have various oxidation states, but the most common is +3
•       Both lanthanoid and actinoid are electropositive, which makes them very reactive
•       They have contraction properties
•       They are paramagnetic
•       They show lanthanoid and actinoid contraction due to poor shielding of 4f orbitals

Conclusion

f orbitals are known as inner transition elements because of the entering of valence shell electrons into (n-2)f orbitals.

They show many properties in which lanthanide contraction catches our attention because of the poor shielding effects of 4f orbitals; it results in a smaller size of lanthanides. They are found naturally on earth, and also some are artificial too. most of them are radioactive