Curium (Cm) belongs to 5f series. Its atomic number is 96. Which of the following is the correct electronic configuration of Curium?

$[Rn]5f^76d^17s^2$

The correct answer is Option (1) → $[Rn]5f^76d^17s^2$

To determine the correct electronic configuration for Curium (Cm), we need to look at its position in the periodic table and the rules of stability for electron subshells.

1. Identify the Basics

• Atomic Number (Z): 96
• Series: Actinide (5f) series
• Nearest Noble Gas: Radon (Rn), which has an atomic number of 86

This means we need to account for 96 - 86 = 10 valence electrons.

2. Filling the Subshells

Normally, according to the Aufbau principle, the $7s, 5f$, and 6d orbitals are filled in that order. However, half-filled and fully-filled subshells offer extra stability.

• $7s$ subshell: Takes 2 electrons ($7s^2$).
• $5f$ subshell: Ideally, it would take the remaining 8 electrons ($5f^8$).
• Stability Exception: A half-filled $f$ subshell ($f^7$) is exceptionally stable. To achieve this, Curium "shifts" one electron to the 6d orbital.

3. The Final Configuration

By keeping the 5f orbital half-filled, the configuration becomes: $[Rn]5f^76d^17s^2$

Summary of Choice

The correct option is the first one: $[Rn]5f^76d^17s^2$.