Which statement best describes how electrons fill orbitals in the periodic table?

• A. Electrons fill all p orbitals before any s orbitals.
• B. Electrons always pair up in an orbital before occupying separate orbitals of the same energy.
• C. Electrons fill orbitals randomly without regard to energy levels.
• D. Electrons fill orbitals in order of increasing energy, following the Aufbau principle.

Answer: (D)

Verified step by step guidance

1. Understand that electrons fill atomic orbitals according to specific rules that minimize the energy of the atom.
2. Recall the Aufbau principle, which states that electrons occupy orbitals starting from the lowest energy level to higher energy levels sequentially.
3. Remember Hund's rule, which says that electrons will fill degenerate orbitals (orbitals of the same energy) singly first, before pairing up, to minimize electron repulsion.
4. Note the Pauli exclusion principle, which states that an orbital can hold a maximum of two electrons with opposite spins.
5. Combine these principles to conclude that electrons fill orbitals in order of increasing energy, not randomly, and do not fill all p orbitals before s orbitals; instead, they fill the 4s orbital before the 3d, for example.