Problem 49 - A Complete Resource Book in Chemistry for JEE Main

Question

Lanthanoides are (a) 14 elements in the VI period (atomic number \(=58\) to 71 ) that are filling the \(4 \mathrm{f}\)-sublevel (b) 14 elements in the VII period (atomic number = 50 to 71 ) that are filling the \(4 \mathrm{f}\)-sublevel (c) 14 elements in the VII period (atomic number = 90 to 103 ) that are filling the 5 f-sublevel (d) 14 elements in the VI period (atomic number \(=90\) to 103 ) that are filling the \(4 \mathrm{f}\)-sublevel

Step-by-Step Solution

Answer

Option (a) is correct; lanthanoides are 14 elements in the VI period filling the \(4f\)-sublevel.

Step 1: Understanding Lanthanoides

The lanthanoid series includes elements characterized by the filling of the \(4f\) sublevel. These elements belong to the f-block of the periodic table.

Step 2: Identifying the Lanthanoid Elements

The lanthanoides are specifically the 14 elements from atomic number 58 to 71. This range corresponds to a continuous filling of the \(4f\) sublevel in the periodic table.

Step 3: Periodicity of Lanthanoides

Elements with atomic numbers from 58 to 71 occur in Period VI of the periodic table. All lanthanoides are therefore listed as part of the 6th period, where the \(4f\) sublevel is being filled.

Step 4: Analyzing Each Option

- Option (a) correctly describes the lanthanoides as 14 elements in the VI period (atomic number \(=58\) to 71) that fill the \(4f\)-sublevel.- Option (b) incorrectly places the elements in the VII period.- Option (c) incorrectly describes elements filling the \(5f\)-sublevel, which pertains to actinides.- Option (d) incorrectly combines elements from a higher period with a different sublevel fill.

Step 5: Conclusion

Based on the description and properties of lanthanoides, the correct choice is option (a), which matches the known characteristics best.

Key Concepts

4f sublevel

The concept of the "4f sublevel" is fundamental in understanding the electron configuration of lanthanoides. Atoms are composed of different levels and sublevels where electrons reside. The 4f sublevel refers to a specific type of orbital found in atoms that can hold up to 14 electrons. This is part of the f-block elements and is distinguished by its complex shapes. The sublevel typically begins filling after the 6s orbital, typically starting in elements of Atomic Number 58, with Cerium. The specific electron configuration for these orbitals is what gives the lanthanoides their unique chemical properties.
f-type sublevels, like the 4f, are located beneath the valence electrons and involve inner electron filling.
This behavior results in lanthanoides having large atomic and ionic sizes due to the decreasing effect of effective nuclear charge on outer electrons.

Periodic Table

The periodic table is a comprehensive chart organizing all known elements based on their atomic number. Lanthanoides fit within this structure in a unique way, mostly classified as part of the f-block.
Visual learners refer to the periodic table to understand how these elements behave similarly due to their grouping. Lanthanoides are located in a specific row down below the main block of the table, known as a "footnote" line. This organization helps chemists visualize the relationships and properties lanthanoides share, such as having similar oxidation states due to their electron configuration. The periodic table structure is thus crucial in predicting element reactions and behavior.

Period VI

Period VI on the periodic table includes the lanthanoid series, which stretches from Cerium (Ce, atomic number 58) to Lutetium (Lu, atomic number 71). Placing these elements in Period VI highlights their distinguishable electron filling sequence. Here, electrons enter into the 4f sublevel, contributing to the unique characteristics and often making them very similar in their chemical reactions and properties.
Period VI is notable because it showcases elements that transition beyond the d-block into the f-block, resulting in elements that have increasingly complex inner electron structures as their atomic numbers rise. These inner structures are responsible for unique characteristics like color variability and magnetic properties.

f-block elements

The f-block elements, often referred to as the "inner transition metals," include both lanthanoides and actinides. The term "f-block" derives from the filling of the f-orbitals with electrons. Lanthanoides are the first series of these elements, beginning with atomic number 58 (Cerium) and ending with 71 (Lutetium).
F-block elements share complex electron configurations because they involve the filling of the 4f and 5f sublevels.

• Lanthanoides are specifically concerned with the 4f sublevel's filling, resulting in unique properties like luminescence and high magnetic susceptibility.
• Their placement as f-block elements means they do not follow traditional element sequence patterns found in the d-block or p-block.

Overall, understanding the f-block is key for studying why certain elements exhibit such rich and varied chemical and physical behaviors.