F-Block Elements in Chemistry, also known as Inner Transition Elements, comprise a group of elements located in the two rows at the bottom of the periodic table. Elements with filled f orbitals are found within this section. The f-block is positioned in the sixth and seventh periods of the periodic table, with the sixth period referred to as the lanthanide series and the seventh as the actinide series.
In this article, we will discuss the topic of F-Block Elements, including their properties, position in the periodic table, electronic configurations, as well as their real-world applications.
Table of Content
What are F Block Elements?
F-Block elements are those in which the last electron enters any of each seven F orbital of their ante-penultimate shell. The electrons in these elements are distributed as follows: (1 to 14) in the f orbital, (0 to 1) in the d orbital of the penultimate energy level, and (0 to 1) in the outermost orbital.
There are fourteen elements in each series that occupy the ‘F’ orbital. The F-block is situated between groups 3 and 4 in the sixth and seventh periods of the periodic table.
F-Block Elements as Inner Transition Elements
F-Block Elements are often referred to as Inner Transition elements because they are positioned within the Transition metals, forming a bridge between the s-block and d-block elements on the left side of the periodic table and the p-block elements on the right side.
The inner transition elements include the lanthanides (4f-series) and actinides (5f-series). The term “Inner Transition” emphasizes the fact that the F-block elements have their outermost electrons filling the F orbitals, which are inner electron shells.
Electronic Configuration of F Block Elements
The electronic configuration of the F-block elements, specifically the lanthanides (4f-series) and actinides (5f-series), can be understood by looking at the filling of their F orbitals.
General Electronic Configuration
The general electronic configuration of F-block elements is : (n-2) f1-14 (n-1) d0-2 ns2. The elements included in these two series are called the Inner Transition Elements.
- Lanthanides (4f-series): The general outer electronic configuration for the Lanthanides is [Xe] 6s2 4f1 where i represents the position of the specific lanthanide in the series. Each lanthanide element has an increasing value of n (the principal quantum number) for the 4f orbitals.
For example, for Cerium (Ce), the electronic configuration would be [Xe] 6s2 4f1, and for lutetium (Lu), it would be [Xe] 6s2 4f14.
- Actinides (5f-series): The general outer electronic configuration for the Actinides is [Rn] 7s25f1 where i represents the position of the specific actinide in the series. The actinides have increasing values of n for the 5f orbitals.
For example, for uranium (U), the electronic configuration would be [Rn] 7s1 5f3, and for lawrencium (Lr), it would be [Rn] 7s2 5f14 7p1.
Anomalous Electron Configurations
The anomalies arise due to the complex interplay of electron-electron repulsions, shielding effects, and the energy levels of orbitals, and they deviate from the expected patterns seen in simpler electron configurations.
The competition between different energy levels and subshells can lead to these anomalies in the electron configurations of F-Block elements. Some examples are:
- Ytterbium (Yb): Ytterbium exhibits an anomalous electron configuration, [Xe] 6s2 4f14 5d1 6p0, instead of the expected [Xe] 6s² 4f14 5d¹. This anomaly is again attributed to the stability of having a half-filled 5d subshell.
- Thorium (Th): Thorium has an anomalous electron configuration of [Rn] 7s2 5f0 6d2 7p0, rather than the expected [Rn] 7s2 5f1 6d1 7p0. The stability of a half-filled 6d subshell is thought to be the reason for this anomaly.
F-Block Elements in Periodic Table
F-block elements are located at the bottom of the periodic table. They include the lanthanides (from atomic number 57 to 71) and actinides (from atomic number 89 to 103).
Read More about Periodic Table of Elements.
Classification of F Block Elements
F-block elements, also known as Inner Transition elements, are classified into two main groups:
- Lanthanides (4f-series)
- Actinides (5f-series)
This classification is based on the filling of f orbitals and the resulting electronic configurations of these elements.
Lanthanides (4f-series)
Lanthanides consist of 15 elements, starting with lanthanum (La) and ending with lutetium (Lu), from atomic numbers 57 to 71. They are characterized by the filling of the 4f orbitals. Lanthanides are often collectively referred to as the “rare earth elements.” They share similar chemical properties due to the gradual filling of the 4f orbitals, resulting in comparable outer electron configurations.
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Actinides (5f-series)
Actinides comprise 15 elements, starting with actinium (Ac) and extending beyond uranium (U) to lawrencium (Lr), covering atomic numbers 89 to 103. They are characterized by the filling of the 5f orbitals. Actinides are radioactive in nature and also undergo radioactive decay, emitting alpha, beta, and gamma radiation. Some actinides, such as americium (Am) and curium (Cm), are used in research and industrial applications.
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Properties of F Block Elements
The F-block elements, comprising the Lanthanides (4f-series) and Actinides (5f-series), possess unique properties and some of the key properties of F-block elements are :
- Radioactivity: Many actinides are radioactive. The level of radioactivity increases with higher atomic numbers.
- Colorful Ions: F-block elements, especially lanthanides, can form colorful ions and complexes, leading to their use in various color applications.
- Variability in Oxidation States: F-block elements often exhibit multiple oxidation states. The stability of different oxidation states varies within the series.
Characteristics of Lanthanides
Lanthanide exhibit several unique characteristics that distinguish them from other elements. Some of the key characteristics of the lanthanides are :
- Metallic Properties: Lanthanides are metals with typical metallic properties, including high electrical conductivity. They have a shiny appearance and can be ductile and malleable and have magnetic properties also due to unpaired electrons.
- High Melting and Boiling Points: Lanthanides generally have high melting and boiling points, contributing to their use in various high-temperature applications and are also good conductors of heat and electricity.
- Ionization Energy: Lanthanides generally have relatively high ionization energies, reflecting the difficulty of removing electrons from the inner 4f orbitals.
- Similar Chemical Properties: Lanthanides share similar chemical properties due to the gradual filling of the 4f orbitals, resulting in comparable outer electron configurations. They often form color compounds and ions.
Characteristics of Actinides
Actinides are a series of chemical elements found in Group 3 of the periodic table and its important characteristics are:
- Complex Electronic Structure: Actinides have complex electronic structures due to the filling of 5f orbitals. This complexity leads to variations in their chemical and physical properties.
- Multiple Oxidation States: Actinides exhibit multiple oxidation states, and their chemistry is characterized by the ability to form a wide range of compounds. Common oxidation states include +3, +4, +5, +6, and +7.
- Fission Properties: Many actinides, particularly uranium and plutonium, are important in nuclear fission reactions. Uranium-235, for example, is used as a fuel in nuclear reactors.
- Radioactive Decay Series: Actinides often participate in radioactive decay series. For example, uranium-238 undergoes a series of decays to eventually become stable lead-206.
Difference between Lanthanoid and Actinide
Some of the common differences between lanthanoid and actinide are:
|
Lanthanoid |
Actinide |
|---|---|
|
Lanthanides starts from lanthanum (La) and ends with lutetium (Lu), spanning atomic numbers 57 to 71. |
Actinides, starts from actinium (Ac) and extends down to lawrencium (Lr), covering atomic numbers 89 to 103. |
|
Lanthanides share similar chemical properties due to the filling of the 4f orbitals and also exhibit Lanthanoid contraction |
Actinides, while also having similar chemical properties, exhibit a wider range of oxidation states compared to lanthanides. |
|
Some Lanthanides have stable isotopes, and their radioactive isotopes have relatively long half-lives. |
Many actinides, especially the heavier ones, have unstable and radioactive isotopes with shorter half-lives. |
Difference between Lanthanoid and Actinide Contraction
Some of the most common differences between lanthenoid and actinide contraction are listed in the following table:
|
Lanthanoid Contraction |
Actinide Contraction |
|---|---|
|
It refers to the phenomenon where there is a decrease in the atomic and ionic radii of the elements in the lanthanide series |
The Actinide series does not show a similar contraction effect, mainly because the 5f electrons are not as effective at shielding the nuclear charge as the 4f electrons in the lanthanide series |
|
Due to the poor shielding of 4F electrons which leads to a stronger effective nuclear charge felt by the outer electrons, causing a contraction in the atomic and ionic radii. |
Due to 5F electron which leads to very poor shielding effect due to which this effect is not pronounced. |
|
The lanthanoid contraction has several consequences in terms of properties such as atomic size, ionization energy, and chemical behavior across the lanthanide series. |
The properties of Actinides are influenced by their electronic configuration, including the filling of 5f orbitals, but the Actinide contraction is not used. |
D & F Block Elements
D-block and F-block elements are two categories of transition metals found in the periodic table, and they differ in their electron configurations, properties, and where they are located on the periodic table.
Some common differences are listed in the following table:
| Property | D-Block Elements | F-Block Elements |
|---|---|---|
| Location in the Periodic Table | Found in groups 3 to 12 | Found in two rows at the bottom of the periodic table (lanthanides and actinides). |
| Valence Electrons | The outermost (valence) electrons are primarily responsible for their chemical properties | The outermost (valence) electrons are primarily responsible for their chemical properties |
| Size | Generally smaller in size compared to F-block elements | Generally larger in size due to the presence of additional electron shells |
| Magnetic Properties | Exhibit magnetic properties, with some exceptions | Exhibit strong magnetic properties due to unpaired electrons in 4f and 5f orbitals |
| Filling of Electron Shells | Filling of electron shells follows Hund’s rule and Aufbau principle | Filling of electron shells is complex and follows the Aufbau principle with Lanthanide contraction effect |
| Applications | Used in various everyday items, including transition metals like iron, copper, and zinc | Some actinides have applications in nuclear reactors and the nuclear industry |
| Atomic Numbers | Atomic numbers range from 21 (Scandium) to 30 (Zinc) and beyond | Atomic numbers range from 57 (Lanthanum) to 71 (Lutetium) for lanthanides and 89 (Actinium) to 103 (Lawrencium) for actinides |
Applications of F Block Elements
The F-block elements, which include the Lanthanides and Actinides have several important applications across various fields. Important applications of F-block elements are :
- Lanthanides in Catalysts: Lanthanides such as cerium, praseodymium, and neodymium are used as catalysts in various industrial processes. For example, cerium oxide is used in automotive catalytic converters to reduce emissions.
- Magnetic Properties: Some F-block elements, especially the lanthanides, exhibit strong magnetic properties. Gadolinium, for instance, is used in magnetic resonance imaging (MRI) as a contrast agent due to its magnetic properties.
- Medicine: Some Lanthanides have medical applications. Gadolinium is used as a contrast agent in MRI scans, and samarium is used in the treatment of certain types of cancer.
- Lighting and Display Technologies: Europium and terbium, two lanthanides, are used in the production of phosphors for fluorescent lamps and LED screens. These phosphors emit light in response to excitation, contributing to the color display.
- Radioactive Dating: Thorium and uranium isotopes are used in radioactive dating techniques to determine the age of rocks and archaeological artifacts.
Conclusion
F-block elements, also known as inner transition elements encompassing both Lanthanides and Actinides, exhibit a wide range of applications across different scientific, industrial, and technological domains. Their unique electronic configurations and properties make them indispensable in various processes.
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Sample Questions on F Block Elements
Question 1: Why are F-Block elements placed at the bottom of the periodic table?
Answer:
F-block elements are placed at the bottom of the periodic table to conserve space, with their positions indicated separately in the form of the lanthanide and actinide series.
Question 2: What is the significance of Lanthanides in Catalysis?
Answer:
Lanthanides are used as catalysts in various industrial processes due to their unique electronic properties, which influence reaction rates and selectivity.
Question 3: What is the shape of the F-Block element?
Answer:
The F – orbital, which has 15 protons, completes the fifth level of a tetrahedral structure. The F – orbital is more complicated than the p and d orbitals, but it follows the same proton alignment rules. When fully loaded, it resembles the d orbital but is cut in half (eight lobes instead of four).
Question 4: Why are Lanthanides preferred for creating Phosphors in LED screens?
Answer:
Lanthanides are preferred for creating phosphors in LED screens for several reasons: Efficient Luminescence, Narrow Emission Bands , High Quantum Efficiency, Low Sensitivity to Temperature, etc . Overall, the unique optical and chemical properties of lanthanides make them ideal candidates for phosphors in LED screens.
Frequently Asked Questions on F Block Elements
What are Inner Transition Elements?
Inner transition elements, also known as f-block elements, are a group of elements found in the two bottom rows of the periodic table (lanthanides and actinides). They have partially filled f-orbitals.
Why F-Block Elements are Called Inner Transition Elements?
F-block elements are called Inner Transition elements because they involve the filling of innermost F-orbitals during electron configuration.
Write name of Five F-Block Elements.
Five f-block elements are:
- Lutetium (Lu)
- Hafnium (Hf)
- Uranium (U)
- Neptunium (Np)
- Curium (Cm)
What is General Electronic Configuration of F-Block Elements?
The general electronic configuration of f-block elements is [noble gas] 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f1-14 5s2 5p6 5d10 5f1-14 6s2 6p2. The f-orbitals are being filled.
What is key Difference Between Lanthanide and Actinide?
The key difference between lanthanides and actinides is their placement on the periodic table. Lanthanides are in the f-block from atomic number 57-71, while actinides are from 89-103.
What is Lanthanoid Contraction?
Lanthanoid contraction is the decrease in atomic and ionic radii of elements in the lanthanide series, caused by poor shielding of the increasing nuclear charge as electrons fill the 4f orbitals.
Are all F Block Elements Radioactive?
No, not all F-block elements are radioactive. Some, like lanthanides and actinides, have radioactive isotopes, but not all of them are inherently radioactive.