Inner transition elements are indeed the elements wherein the last electron enters in the f-orbital. Inner transition elements usually correspond to group 3 in the periodic table but are noted individually as the f block elements. These f block elements are considered as inner transition elements. The inner transition elements are classified into two groups: lanthanide (formerly referred to as lanthanides) and actinoids (previously called actinides).

Inner transition elements are often shown below all other elements in the normal periodic table view but really belong to periods 6 and 7. Cerium through lutetium (atomic numbers 58–71) comprise the lanthanide series, which follows lanthanum. 

Similarly, the actinide series includes the 14 elements thorium through lawrencium (atomic numbers 90–103), which follow actinium. These elements were discovered and added to the periodic table quite recently. Numerous actinides are not naturally occurring but were produced through nuclear processes. Chemically, the elements in each family (particularly the lanthanides) are quite similar. 

Numerous lanthanides are employed in the manufacture of lasers, optical lenses, and powerful magnets. To this date, rocks, minerals, and fossils are utilised in certain radioactive isotopes of inner transition elements. Uranium (U) and plutonium (Pu) are the two most well-known actinoids used in atomic warheads and nuclear power plants to produce energy.

Transition elements are defined  as elements with partly filled d orbitals (or those that easily create them). The d-block components in groups 3–11 are transition elements

The f-block elements, also known as inner transition elements (lanthanides and actinides), also satisfy this condition due to the fact that the d orbital is partly filled prior to the f orbitals. The copper family (group 11) fills the d orbitals; hence, the next family (group 12) is technically not a transition element. However, the group 12 elements have certain chemical characteristics with transition metals . Certain scientists do classify the elements of group 12 as transition metals.

Inner Transition Elements

There are two distinct series of internal transition elements-

• Lanthanide series- When the last electron reaches the 4f orbital, the series is said to be lanthanoid
• Actinide series- A series is considered to be actinoid if the last electron reaches the 5f orbital
• We shall examine the primary properties of inner transition components in this post
• Additionally, the distinctions and similarities between lanthanoids and actinoids are discussed.

Lanthanoids’ Primary Characteristics: 

• Atomic radii: As the series progresses, the atomic radii of lanthanides shrink noticeably. This is related to the contraction of the lanthanoid. Lanthanoid contraction may be characterised as the 4f orbitals weak shielding effect, which causes the positive nuclear charge to have a greater influence on the outermost electron, lowering the series’s atomic radii
• Lanthanoids undergo the most frequent oxidation state, which is +3. Occasionally, they exhibit +2 and +4 oxidation states as well. This difference is due to the increased stability of an empty, partly filled, or completely filled f-orbital
• Because they are mostly metals, they are excellent conductors of heat and electricity. Metals get harder as their atomic number rises
• Due to the presence of electrons in the f- orbital, they produce coloured ions (narrow absorption bands).

Actinoid’ Primary Characteristics: 

• Atomic radii: As the series progresses, the atomic radii of actinides shrink significantly. This is related to the contraction of the actinoid. Actinoid contraction is described as the insufficient shielding effect of the 5f orbital, which allows the positive nuclear charge to have a greater influence on the outermost electron, hence lowering the atomic radii in the series
• The most often seen oxidation state in actinoids is +3. (but not stable necessarily)
• Metals known as actinides are very reactive
• In nature, actinides are mostly radioactive.
• They are synthesized and are not present naturally in the earth’s crust
• Lanthanide: between cerium (Z=53) and lutetium (Z=71)
• actinides starting with thorium (Z = 90) and ending with lawrencium (Z = 103).

• Transition elements are defined as those with a partly filled d or f subshell in any common oxidation state. Typically, the word “transition elements” refers to d-block transition elements. Zinc, cadmium, and mercury are 2B elements that do not technically match the defining characteristics but are often listed with the transition elements due to their comparable qualities. f-block transition elements are sometimes referred to as “interior transition elements.” Their first row is referred to as lanthanides or rare earth. The second row is made up of actinides. All actinides are radioactive, and those with a Z greater than 92 are synthesised in nuclear reactors or accelerators.
• The transition elements’ general attributes are as follows:
• Typically, these are metals with a high melting point
• They exist in a variety of oxidation states
• Typically, they produce colourful compounds
• Frequently, they are paramagnetic
• Iron, copper, and silver are all significant transition elements. The most prevalent transition elements are iron and titanium. Numerous industrial catalysts include transition elements.

Transition Metal Properties and Trends

As predicted, the elements in the second and third rows of the Periodic Table exhibit steady changes in characteristics from left to right across the table. Electrons in these elements’ outer shells have negligible shielding properties, resulting in a rise in effective nuclear charge due to the addition of protons to the nucleus. As a result, the following impacts on atomic characteristics occur decreased atomic radius, increased initial ionisation energy, greater electronegativity, and enhanced nonmetallic character. This pattern continues until calcium (Z=20) is reached. At this moment, there is an abrupt pause. The following 10 elements, referred to as the first transition series, have remarkable physical and chemical features. This overall agreement in attributes has been ascribed to the series’s very tiny effective nuclear charge difference. This happens due to each extra electron entering the penultimate 3d shell, effectively shielding the nucleus from the outer 4s shell.

First, it is necessary to distinguish the transition elements’ physical and chemical characteristics from those of the main group elements (s-block). Among the properties of transition elements are the following:

Have a high charge/radius ratio; are dense and have high melting and boiling temperatures; produce paramagnetic compounds; exhibit varied oxidation states; form coloured ions and compounds; form compounds with significant catalytic activity; create stable complexes.

The transition elements are much denser than the s-block elements, increasing in density gradually from scandium to copper. This density trend may be explained by the slight and irregular drop in metallic radii in conjunction with the relative rise in atomic mass.

Transition metals have high melting temperatures and molar enthalpies of fusion in contrast to main group elements. This is due to the strong metallic bonding that occurs in transition metals due to electron delocalisation assisted by the presence of both d and s electrons.

Conclusion 

• Comparative Properties of Lanthanoids and Actinoids
• The filling of the last electron into the 4f orbital results in the element being classified as a member of the first series of transition elements. Following lanthanum, the lanthanide series has 14 elements. These are called lanthanides or lanthanoids because they come directly after lanthanum in the periodic table. Although lanthanum lacks 4f electrons, it is often included in lanthanide due to its strong resemblance to lanthanoids
• Actinides are the electrons formed by successively filling 5f orbitals. They are so-called because they come directly after actinium in the periodic table (Ac). The sequence of actinides is composed of fourteen elements ranging from Th(90) to Lw(103). It is sometimes referred to as the second series of inner transitions. Because actinium (Z=89) lacks 5f electrons, it is common to analyse it using actinoids.