F block elements of the periodic table consist of Lanthanide and Actinide Series. The f block appears as a footnote in a standard 18-column table but is located at the centre-left of a 32-column full-width table. In this article, we will learn about f blocks in detail along with their Electronic Configuration, Occurrence, Physical properties, and Chemical Properties.

 Also read about the blocks of the periodic table here.

What are F Block Elements?

The elements in which the differentiating electron enters into (n–2) f orbital are known as f block elements. They are also called inner transition elements, due to their position and properties. They belong to the third group of the periodic table. There are two series of f-block elements, 4f series (lanthanoid) and 5f series (actinoid). f0, f7, f14 electronic configurations achieve extra stability due to empty, half-filled and completely filled orbitals respectively.

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While these elements are generally not considered part of any group, some authors consider them to be part of group 3. They are sometimes called inner transition metals because they provide a transition between the s-block and d-block in the 6th and 7th row (period), in the same way that the d-block transition metals provide a transitional bridge between the s-block and p-block in the 4th and 5th rows.

The f-block elements come in two series, in periods 6 and 7. All are metals. The f-orbital electrons are less active in the chemistry of the period 6 f-block elements, although they do make some contribution: these are rather similar to each other.

With one 5d and two 6s electrons, lanthanum is the first element in the third transition series. Cerium comes next; it still has two 6s electrons but has two in the 4f orbitals and none in the 5d orbitals. There are seven different 4f orbitals, and each one can hold two electrons with opposing spins.

From cerium to lutetium, the atoms have two to fourteen electrons in 4f- orbitals, respectively. Although lanthanum itself doesn’t have any 4f electrons, it is common to place it in this series together with the other elements that make up the first inner transition series known as lanthanides.

The general valence shell electronic configuration of lanthanides

[X e] 4 f^{0,2} \text { to } 145 d^{0 \text { to } 16 s^2}

Lanthenide series (4f-block elements)

The second series of 5f block chemical elements results from the filling of 5f-orbital. Actinides in f block consist of chemical elements like thorium to lawrencium with atomic numbers 90 to 103.

The general electronic configuration of 5f-block elements or actinides is

[Rn] 5f¹–¹⁴ 6d⁰–¹ 7s²

Actinides (5f-block Elements)

Read about electronic configuration here.

Characteristics of F Block Elements.

F- block elements, comprising lanthanides and actinides are characterized by the gradual filling of 4f and 5f orbitals. They typically exhibit variable oxidation states, high melting points, and form colored ions. Many typically are also paramagnetic and show complex formation tendencies.

• They are heavy metals. They are hard metals.
• They generally have high melting and boiling points.
• They exhibit variable oxidation states.
• They form coloured ions.
• They have the tendency to form complex compounds.
• Actinides are radioactive in nature.
• Lanthanide oxides come in use in cleaning glass as abrasives.
• They show magnetic properties.
• With an increase in atomic number, there is a decrease in atomic and ionic size.
• They are involved in the filling of (n-2) f orbitals.
• They are highly electropositive and very reactive in nature.

Parts of F Block Elements

The f block element is made up of two series: Lanthanoid Series and Actinoid Series.

Lanthanide

Lanthanide Series are f block elements in which the differentiating electron enters into 4f orbital. Hence this series is also called the 4f series. The common oxidation state of all lanthanides and actinides is +3. Some of the lanthanides also show +2 and +4 oxidation states. Lanthanides form carbides, hydrides, oxides, nitrides, halides etc. The atomic and ionic radii of lanthanides show a gradual decrease with an increase in atomic number. It is known as lanthanoid contraction.

The effect of contraction is a decrease in basicity with an increase in atomic number. As a result of lanthanoid contraction, the atomic radii of the elements which follow lanthanides are similar to those of the elements of the previous period. The pairs of elements Zr-Hf, Nb-Ta, Mo-W and Tc-Re have identical sizes, and similar properties hence these pairs are called chemical twins.

Know more about Isomerism, here.

Properties of Lanthanides

• The elements of the lanthanide series are characterized by the preferential filling of 4f orbital.
• This series includes elements from Cerium (Z=58) to Lutetium (Z=71), a group of 14 elements with differentiating electrons occupying a 4f subshell.
• The name lanthanide has been derived from lanthanum which is the prototype of lanthanide.
• The fourteen elements from cerium to lutetium constitute the lanthanoid series and are called lanthanides.
• These elements are within the transition series and their inner shells (n=2) f i.e. 4f and (n-1) d i.e. 5d are incomplete.
• General electronic configuration of 4f elements is Xe 4f1-145d0-1 6s2

Actinides

Actinide Series are f block elements in which the differentiating electron enters into the 5f orbital. Hence this series is also called the 5f series. The common oxidation state of all lanthanides and actinides is +3. In the actinoid series, the elements after uranium are man-made elements hence are called transuranic and synthetic elements. They belong to the 3rd group and the seventh period of the periodic table. The most common oxidation state is +3. Some elements also show +4, +5, +6, +7 oxidation states.

The actinoid elements belong to the second inner transition series in which electrons enter in 5f orbitals (Z = 90 to 103).

Know more about Tautomerism, here.

Properties of Actinides

• Actinium (Z=89) has an electronic configuration [Rn]5
• [Rn]5fo6d17s2. There is no electron in the 5f orbital. The series of elements from Thorium (2=90) to Lawrencium (Z=103) in which 5f orbitals are progressively filled are called actinide.
• The elements are called actinide because many physical and chemical properties are similar to actinium.
• In fact, the name actinoid has been derived from actinium which is the prototype of actinide.
• Actinide constitutes the second inner transition series. In all these elements, the electronic configurations of the outermost as well as the penultimate shell remain the same.
• Because of this arrangement of electrons, elements resemble one another very closely.
• Thorium and uranium metals are obtained from natural sources.
• But elements of Neptunium and successive heavier elements are produced synthetically by the transformation of naturally occurring elements by nuclear reactions.
• These man-made elements having atomic numbers higher than Uranium-92 are collectively called trans-uranic elements. Elements from Rf (Z=104) to Uub (Z=112) have been identified.
• Elements up to atomic number 118 are also synthesized.

Read more about Valence Bond Theory, here.

Difference Between Lanthanides and Actinides

The f block elements of the lanthanide and actinide series involve the filling of orbitals. Lanthanides and actinides have many distinguishing properties.

Also, learn about inner transition elements here.

Similarities between Lanthanide and Actinide

There are some similarities between lanthanoids and actinoids, just as there are differences. Here’s a list of the similarities.

• The two groupings of isostructural, organic and synthetic chemical elements known as actinides and lanthanides each contain fifteen elements.
• The last electron of their atoms enters the f-orbital.
• Actinides and lanthanides share a similar outermost electronic configuration with two s-electron configurations in their outermost electronic shells.
• They are listed below the periodic table in additional rows, with actinium and lanthanum serving as stand-ins for them.
• Among actinides and lanthanides, +3 is the most prevalent oxidation state.
• These elements have a high electropositive and reactive energy.
• These metals have magnetic characteristics and have a silvery-white colour when melted.
• Atomic size decreases when nuclear charge increases and the atomic number rises as a result, according to a study (actinide and lanthanide contraction).
• Actinides and lanthanides have soluble nitrates, sulphates, and perchlorates while insoluble fluorides, carbonates, and hydroxides.

Read about d block elements here.

Uses of F Block Elements

Some examples of how the f block elements can be used are as follows:

• Instrumental steels and heat-resistant materials are made with lanthanide alloys (mischmetals).
• Refractories include lanthanide carbides, borides, and nitrides.
• In order to polish glass, lanthanide oxides are utilized as abrasives.
• Both incandescent gas mantles and the treatment of cancer employ thorium.
• Atomic fuel is made from uranium.
• Nuclear reactors and nuclear weapons both require plutonium.

Check out other topics of Chemistry, here.

Transition Elements in the Periodic Table

Transition elements are found in groups 3 to 12 of the periodic table. These elements are known for having filled d-orbitals in their valence shell. Here’s an organized list of transition metals by period, with their symbols, atomic numbers, and valence shell configurations.

4th Period Transition Elements

5th Period Transition Elements

6th Period Transition Elements

7th Period Transition Elements

These include both actinides (f-block) and d-block elements.

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