Exams Prep Master
Those elements in which the last electron that gets into the f-orbital are known are called the f-block elements or Inner transition elements. Inner transition elements generally are the members of group 3 but they can be seen separately as the f block elements. In the f-block elements the 4f and 5f orbitals are filled. Inner transition elements are the elements belonging to the f-block.
| Table of Content |
The F-block elements are classified into two series- lanthanoids and actinoids. The block of elements are called inner transition metal as they provide a transition in the 6th and 7th row of the periodic table and separates the s block and the d block elements.
Read more: F-Block Elements (Inner Transition Elements)
Definition of F-Block Elements
[Click Here for Sample Questions]
F-Block elements
F-Block elements are the elements in which the last electron enters any one out of seven f-orbitals of their respective ante-penultimate shells. These elements possess electrons, (1 to 14) in the f orbital, (0 to 1) in the d orbital of the penultimate energy level as well as in the outermost orbital. There are mainly two series in the f-block that are equivalent to filling up of 4f and 5f orbitals. The elements include 4f series of Ce to Lu and 5f series of Th to Lw. 14 elements are there that fill up the ‘f’ orbital in each series.
Classification of F-Block Elements
[Click Here for Sample Questions]
Lanthanides and actinides are the two series of the f-block elements or inner transition elements.
- Lanthanide series: The first series of elements are the lanthanides which include elements with atomic numbers from 57 to 71. These elements are non-radioactive (except for promethium). In the lanthanide series the last electron gets into the 4f orbital.
- Actinide series: The second series of elements are actinides which include elements with atomic numbers from 89 to 103. These elements are generally radioactive in nature. In the actinide series the last electron gets into the 5f orbital.
Properties of F-block Elements
- They exhibit variable oxidation states.
- They tend to form complex compounds.
- The third last shell of the inner transition elements is filled with electrons.
- These elements make colorful ions.
- The actinide series elements are radioactive.
- Variable valencies are shown by the inner transition elements.
- Elements beyond atomic number 92 till 103 are synthetic as well as radioactive by nature.
Properties of Lanthanide (Atomic Number: 58 to 71)
The main properties of Lanthanides are given below
- The atomic radius decreases along with the series of lanthanides. The reason for this decrease is lanthanoid contraction. Lanthanoid contraction happens due to the poor shielding of the 4f orbital. Due to this poor shielding, the outermost electron is affected by the positive nuclear charge. Therefore the atomic radius decreases along with the series of the lanthanides.
- Usually, lanthanoids show +3 oxidation states but sometimes they also show up +4 and +2 oxidation states. This variation in the oxidation states is due to the fully filled, partially filled or empty f-orbital.
- The elements in the lanthanide series are generally metals. They are good conductors of electricity and heat. As the atomic number increases the hardness of the metal also increases.
Properties of Lanthanide
Properties of Actinides (Atomic Number: 90 to 103)
- Due to actinoid contraction, the atomic radius decreases along with the series. This contraction happens due to the poor shielding of the 5f orbital. Due to this, the outermost electron is affected by the positive nuclear charge and this decreases the atomic radius along with the actinide series.
- Usually, the most common oxidation state shown by actinoids is +3 (but not stable necessarily)
- The metals in the actinides series are highly reactive.
Properties of Actinides
Electronic Configuration: Lanthanides and Actinides
Lanthanide: 4f1-145p65d0-16s2 {from cerium(Z=53) to Lutetium(Z=71)}
Actinides: 5f1-146s26p66d0-17s2 {from thorium (Z = 90) to lawrencium (Z = 103)}.
Similarities between Lanthanides and Actinides
[Click Here for Sample Questions]
In the first series (lanthanides) of the inner transition elements, the filling of the last electron takes place to the 4f orbital. After lanthanum 14 elements are there, since these elements are after lanthanum the series has been called the lanthanide series. The elements occurring after lanthanum (LA) are Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. Lanthanum does not contain 4f electrons but since it is similar to lanthanoids, it has been added to this series.
In Actinides, the last electron enters the 5f orbital. The name of this series has been given the name of actinium. All the elements occur after actinium, therefore the series has been named the actinide series. Elements after actinium (AC) are Th, Pa, U, Np, Pu, Am, Cm, Bk, Cs, Ef, Fm, Md, No, Lr. Actinium has no 5f electrons; the addition of actinium to the actinide series is customary.
Difference between Lanthanides and Actinides
[Click Here for Sample Questions]
Some of the differences between Lanthanoids and Actinoids have been given below.
| Lanthanides | Actinides |
|---|---|
| The last electron gets into the 4f orbital | The last electron gets into the 5f orbital |
| The electronic configuration of Lanthanoids is : 4f1-145p65d0-16s2 | The electronic configuration of Actinoid is 5f1-146s26p66d0-17s2 |
| The compounds of Lanthanides are less basic | The compounds of actinides are more basic in nature. |
| The elements are non radioactive except promethium. | The elements are radioactive |
| Usually, lanthanoids show +3 oxidation states but sometimes they also show up +4 and +2 oxidation states. | Usually, the most common oxidation state shown by actinoids is +3 |
| Lanthanoids do not form complexes quickly | Actinides form complexes |
Uses of Inner F-Block Elements
[Click Here for Sample Questions]
Some of the important uses of Inner Transition Metals are given below:
- Lanthanides are used for the production of lasers.
- Inner Transition Elements (f-block elements) are used for the determination of age of rocks and fossils. Elements like Samarium and Lutetium are used for this purpose.
- Inner Transition elements are also used for the development of nuclear weapons. Elements like Uranium and Plutonium are used for this purpose.
- Inner Transition Elements are also used for the generation of nuclear power plants.
- Strong magnets are also used with the help of Lanthanides.
- Inner Transition Elements are also used in the field of medical science where they are used for finishing the particular targeted cells in the body. For example uranium protects against radiation.
Things to Remember
[Click Here for Sample Questions]
- The topic “F-Block Elements” is covered in the Unit 3 i.e, Classification of Elements and Periodicity in Properties of NCERT Class 11 Chemistry.
- The entire unit 3 will carry a weightage of 6 periods and around 4 marks in the exam.
- The block of elements is called inner transition metal.
- F-block elements are called inner transition elements as they provide a transition in the 6th and 7th row of the periodic table.
- They are heavy metals.
- They generally have high melting and boiling points.
- They consist of two series: Lanthanides and actinides.
- Lanthanides are generally non-radioactive.
- Actinides are radioactive in nature.
Sample Questions
Ques. What is the other name used for inner transition metals? (1 mark)
Ans. The inner transition elements consist of the lanthanoid series and the actinide series. The elements of these two series are also known as ‘core metals of transition’.
Ques. Do Inner Transition Metals React? (2 marks)
Ans. The inner transition metals are placed at the bottom of the periodic table. These are as reactive as alkali metals. All the actinides are poisonous and therefore the commercial value is zero. However, these metals are used for making nuclear weapons or in the nuclear power plants.
Ques. Why are the transition metals unique? (2 marks)
Ans. The transition metals are unique because they may have an incomplete subshell that permits valence electrons in a shell other than the shell outside. Only some of the elements have valence electrons in the outermost shell. Therefore several oxidation states form the transition metals.
Ques. What is the meaning of transition elements? (2 marks)
Ans. Those elements that have partially filled fords at any rising state of the oxidation are known as the transition elements. Usually, transition element is a term used for the transition elements of the d block.
Ques. Why is the actinoid contraction greater from element to element when compared to lanthanoid contraction? (2 marks)
Ans. The actinoid contraction is greater from element to element because of the poor shielding effect by the electrons of 5f when compared to the electrons of 4f in lanthanide.
Ques. What are the characteristics of f-block elements? (3 marks)
Ans. The characteristics features of f-block elements are:
- The third last shell of the inner transition elements is filled with electrons.
- These elements make colorful ions.
- The actinide series elements are radioactive.
- Variable valencies are shown by the inner transition elements.
- Elements beyond atomic number 92 till 103 are synthetic as well as radioactive by nature.
Ques. What is the electronic configuration of f-block elements? (1 marks)
Ans. The general electronic configuration of f-block elements is:
(n−2) f1 - 14 (n−1) d0-10 ns2
Ques. Why are the f-block elements called inner transition elements? (2 marks)
Ans. The block of elements are called inner transition metal as they provide a transition in the 6th and 7th row of the periodic table and separates the s block and the d block elements.
Ques. What is the last element of the f-block? (1 mark)
Ans. Lawrencium (Lr) is the last element in the series of adenoids which is the second series of the f-block element.
Ques. Why are the f-block elements placed separately? (1 mark)
Ans. The f-block elements are placed apart from the main table primarily in order to conserve space. If these elements were included, the table would have 32 columns.
Ques. Why are lanthanides and actinides placed in separate rows at the bottom of the periodic table? (2 marks)
Ans. The lanthanides and actinides are placed in separate rows at the bottom of the periodic table due to the presence of 4f and 5f orbital in lanthanoids and actinoids. They are also called inner transition elements because of this reason.
Comments