Question

For f block elements shld I remember the configuration or do I need to remember the reason also for their config

Answer 1

You should primarily focus on understanding the reasons for their configurations, including the general trends and the principles behind common exceptions. While remembering a few key configurations can be helpful, conceptual understanding is more valuable.

Answer 2

For f-block elements, it is more beneficial to understand the reasons behind their electronic configurations rather than merely memorizing each one. While knowing the general configuration and a few common exceptions is helpful, a deeper understanding allows you to:

1. Derive Configurations: Understand the general electronic configuration: $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$. For lanthanides, this is typically [Xe]$4f^{1-14}5d^{0-1}6s^2$, and for actinides, it's [Rn]$5f^{1-14}6d^{0-1}7s^2$.
2. Explain Exceptions: Recognize that the energy differences between the $(n-2)f$, $(n-1)d$, and $ns$ orbitals are very small. This leads to exceptions where an electron might enter the $d$-orbital instead of the $f$-orbital (e.g., for elements like Gd, Lu, Cm, Lr) to achieve greater stability (half-filled or completely filled $f$-orbitals, or due to slight energy advantages). Understanding this principle is crucial.
3. Predict Properties: The electronic configuration directly influences the chemical properties, oxidation states, and magnetic behavior of these elements. Understanding the configuration helps in explaining these observed properties.

In summary: Focus on understanding the general rules, the reasons for exceptions, and how the configurations relate to their position in the periodic table. While remembering the exact configurations for a few key elements (especially those with exceptions) can be useful, the underlying principles are far more important for a comprehensive understanding.