Question

The electronic configuration of Pt(atomic number 78) is:

• A. [Xe] 4f¹⁴ 5d⁹ 6s¹
• B. [Kr] 4f¹⁴ 5d¹⁰
• C. [Xe] 4f¹⁴ 5d¹⁰
• D. [Xe] 4f¹⁴ 5d⁸ 6s²

Answer 1

The Correct Option is A

The electronic configuration of an atom describes the distribution of electrons in the orbitals of that atom. To determine the correct electronic configuration for platinum (Pt), which has an atomic number of 78, we need to consider how electrons fill the energy levels and sublevels based on the principles of quantum mechanics.

1. The Aufbau principle states that electrons fill lower-energy orbitals before occupying higher-energy ones.
2. According to Hund's rule, electrons fill degenerate orbitals singly first, before pairing up.
3. The Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers, meaning that an orbital can hold a maximum of two electrons with opposite spins.

Starting from xenon (Xe), which is the closest noble gas with a known configuration, the electronic configuration continues as follows:

• The 4f sublevel is completely filled with 14 electrons after Xe, giving the configuration: 4f^{14}.
• Next, the 5d sublevel starts filling. However, due to the stabilizing effect of a half-filled or fully filled d orbital, one electron from the 6s orbital can be used to complete the 5d sublevel to form a more stable configuration. As such, the configuration becomes 5d^9 6s^1 rather than 5d^8 6s^2.

Thus, the electronic configuration for platinum (Pt) can be written as:

[Xe] 4f¹⁴ 5d⁹ 6s¹

This corresponds to the provided option: [Xe] 4f¹⁴ 5d⁹ 6s¹. All other options either skip important sublevels or incorrectly pair sublevels, making them incorrect based on known principles of electron configuration.