concepts of Aufbau's Principle, Hund's Rule, and Pauli's Exclusion Principle

Aufbau's Principle

• dictates how electrons fill atomic orbitals in an atom.

• Electrons occupy orbitals starting from the lowest energy level to the highest.

• The 1s orbital is filled first, followed by 2s, then 2p, and so on.

• Each electron is added to the lowest available energy level before moving to higher energy levels.

Hund's Rule

• governs how electrons are placed into degenerate (same energy) orbitals.

• Electrons fill degenerate orbitals with parallel spins (arrows pointing in the same direction) before pairing up.

• Unpaired electrons are more stable than paired electrons due to electron-electron repulsion.

• Orbitals are filled one electron at a time with parallel spins before any orbitals are doubly occupied.

Pauli's Exclusion Principle

states that no two electrons in an atom can have the same set of four quantum numbers.

• n (Principal Quantum Number)

• l (Angular Momentum Quantum Number)

• ml (Magnetic Quantum Number)

• ms (Spin Quantum Number)

The four quantum numbers (n, l, ml, ms) uniquely describe each electron

n

Principal Quantum Number

l

Angular Momentum Quantum Number

ml

Magnetic Quantum Number

ms

Spin Quantum Number

n (Principal Quantum Number)

Describes the energy level.

l (Angular Momentum Quantum Number)

Describes the shape of the orbital (s, p, d, f).

ml (Magnetic Quantum Number)

Describes the orientation of the orbital in space

ms (Spin Quantum Number)

Describes the spin of the electron (+1/2 or -1/2)