Question

The electronic configurations of Eu (Atomic No. 63), Gd(Atomic No. 64) and Tb (Atomic No. 65) are:

• A. ${[Xe]^4f^6 5d^1 6s^2, [Xe]^4f^75d^16s^2}$ and ${[Xe]^4f^9 6s^2}$
• B. ${[Xe]^4f^65d^16s^2, [Xe]^4f^75d^16s^2}$ and ${[Xe]^4f^85d^16s^2}$
• C. ${[Xe]^4f^7 6s^2, [Xe] 4f^75d^16s^2}$ and ${[Xe]4f^96s^2}$
• D. ${[Xe]4f^76s^2, [Xe]4f^86s^2}$ and ${[Xe]4f^85d^16s^2}$

Answer 1

The Correct Option is C

To determine the electronic configurations of Europium (Eu), Gadolinium (Gd), and Terbium (Tb), we need to understand their positions in the periodic table and the distribution of electrons in their atomic orbitals. These elements are part of the lanthanide series.

1. Europium (Eu): The atomic number of Eu is 63. It follows Xenon ([Xe]), and the electrons fill the 4f, 5d, and 6s orbitals as follows:
   • The 4f orbitals can hold a maximum of 14 electrons, and for Eu, it fills up to 7 electrons due to its position in the series.
   • The electronic configuration is [Xe]4f^7 6s^2 since the 5d orbital is not yet filled in Europium.
2. Gadolinium (Gd): Gd has an atomic number of 64. Once again starting from Xenon ([Xe]):
   • It has one more electron than Eu, which fills the next available orbital after 4f^7.
   • This additional electron goes into the 5d orbital, resulting in the configuration [Xe]4f^7 5d^1 6s^2.
3. Terbium (Tb): Tb with atomic number 65 also follows the sequence after Gd:
   • It adds one more electron to the 4f series, resulting in 4f^8.
   • The configuration becomes [Xe]4f^9 6s^2 as the 5d^1 becomes 4f^9 to maintain Hund's rule of maximum multiplicity.

Now let's match these configurations with the given options:

1. The option [Xe]^4f^7 6s^2, [Xe] 4f^75d^16s^2 and [Xe]4f^96s^2 corresponds correctly to Eu, Gd, and Tb;

Therefore, the correct answer is: ${[Xe]^4f^7 6s^2, [Xe] 4f^75d^16s^2}$ and ${[Xe]4f^96s^2}$.