F-Block Elements | Lanthanides & Actinides

Here we discussed the introduction to f-block elements, the position of f-block elements in the periodic table, classification, electronic configuration, characteristics, and the difference between lanthanides and actinides. The elements from cerium (Z=58) to lutetium (Z=71) and from thorium (Z=90) to lawrencium (Z=103) are called inner-transition elements or f-block elements.

f-block elements

Position of F-block Elements in the Periodic Table

F-block elements are placed at the bottom of the periodic table. The first series of fourteen elements lies between lanthanum (Z=57) and hafnium (Z=72) in the 6th period while the second series of fourteen elements lies between actinium (Z=89) and rutherfordium (Z=104) in the 7th period of the periodic table. The elements of the first series from La (57) to Lu (71) are called lanthanides. The lanthanides are also called lanthanones or rare earth elements. The elements of the second series from Ac (89) to Lr (103) are called actinides. The actinides are also known as actinones.

What are F-block Elements Names?

Lanthanides and actinides are f-block elements. The names of elements with atomic numbers, symbols, atomic masses, and oxidation states are given below:

Lanthanide Elements

Atomic No.ElementsSymbolsAtomic massOxidation states
58CeriumCe140.1154,3,2
59PraseodymiumPr140.9074,3,2
60NeodymiumNd144.244,3,2
61PromethiumPm144.91273
62SamariumSm150.363,2
63EuropiumEu151.6953,2
64GadoliniumGd157.253,2,1
65TerbiumTb158.9254,3,1
66DysprosiumDy162.504,3,2
67HolmiumHo164.9303,2
68ErbiumEr167.263
69ThuliumTm168.9343,2
70YtterbiumYb173.043,2
71LutetiumLu174.9673
Atomic no, elements, symbols, atomic masses, oxidation states of lanthanides

Actinide Elements

Atomic No.ElementsSymbolsAtomic massOxidation states
90ThoriumTh232.034,3,2
91ProtactiniumPa231.35,4,3
92UraniumU238.026,5,4,3,2,1
93NeptuniumNp237.047,6,5,4,3,2
94PlutoniumPu244.067,6,5,4,3,2
95AmericiumAm243.067,6,5,4,3,2
96CuriumCm247.076,5,4,3,2
97BerkeliumBk2474,3,2
98CaliforniumCf251.085,4,3,2
99EinsteiniumEs2524,3,2
100FermiumFm257.104,3,2
101MendeleviumMd258.103,2,1
102NebeliumNo256.03,2
103LawrenciumLr262.13,2
Atomic no, elements, symbols, atomic masses, oxidation states of actinides

Why are F-block Elements called Inner Transition Elements?

The elements in which the additional electron (also called differential electron) enter (n-2) f orbital are called f-block elements, where n is the number of shells. f-block elements are also called inner transition elements because the additional electron is not added in the valence shell of an atom, the additional electron is added in (n-2) f orbital which is the “anti-penultimate energy level“. That’s why it is called inner transition elements.

f-block elements are also called inner transition elements

Why 4f Series is called Lanthanides?

Lanthanides are placed in the 6th Period of the periodic table. The 6th period means all the elements of the 6th period have 6 shells and as we discussed above the additional electrons enter in (n -2) f orbital.

(n -2) f orbital

As n = 6

(6-2) f orbital

4f orbital

That’s why 4f Series are called lanthanides. The 4f orbital is also called the first inner transition elements or lanthanide series or rare earth metals.

Why 5f Series is called Actinides?

Actinides are placed in the 7th Period of the periodic table. The 7th period means all the elements of the 7th period have 7 shells and as we discussed above the additional electrons enter in (n -2) f orbital.

(n -2) f orbital

As n = 7

(7-2) f orbital

5f orbital

That’s why 5f Series are called actinides. The 5f orbital is also called the second inner transition element or actinide series or actinone.

What is the General Formula of F-block Elements?

The general outer electronic configuration of f-block elements is (n-2) f0-14, (n-1) d0-1, ns2. The two possible values of n are 6 and 7.

  • If the value of n is 6, then

(n-2) f0-14, (n-1) d0-1, ns2

(6-2) f0-14, (6-1) d0-1, 6s2

4f0-14, 5d0-1, 6s2

The 4f series are known as lanthanides so, this is the general electronic configuration of lanthanide elements.

  • If the value of n is 7, then

(n-2) f0-14, (n-1) d0-1, ns2

(7-2) f0-14, (7-1) d0-1, 7s2

5f0-14, 6d0-1, 7s2

The 5f series are known as actinides so, this is the general electronic configuration of actinide elements.

What are the General Characteristics of F-block Elements or Inner-Transition Elements?

  1. In the inner Transition Elements, the third last shell is in the process of filling with electrons.
  2. The inner transition elements form colored ions.
  3. The inner transition elements show variable valencies.
  4. All actinides are Radioactive by nature.
  5. The inner transition elements beyond atomic number 92 up to 103 are synthetic as well as radioactive. They are not found in nature in the earth’s crust.
  6. All lanthanide elements occur in nature except promethium.
  7. The last electron in the configuration is added to (n-2) f orbitals. Lanthanides and actinides are f-block elements.
  8. All elements are metal.

What is the Difference between Lanthanides and Actinides?

LanthanidesActinides
The last electron enters into a 4f orbital.The last electron enters into a 5f orbital.
The general electronic configuration is 4f0-14, 5d0-1, 6s2.The general electronic configuration is 5f0-14, 6d0-1, 7s2.
The decrease in atomic size is not regular as the decrease in the size of tri-positive ions is regular.There is a gradual decrease in the atomic and ionic (tri-positive ion) size.
The principle and common oxidation state are +3. Some elements also show +2 and +4 oxidation states.The common oxidation state is +3 but it is not always the stable state. The elements in the first half show a higher oxidation state, for example, the maximum oxidation state increases from +4 in Th, +5 in Pa, +6 in U, and +7 in Np.
They do not form complexes readily.They have a much greater tendency to form compounds.
Their compounds are less basic in nature. These elements are non-radioactive except promethium.Their compounds are more basic in nature. They are all radioactive.
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