Principles

Question 1

What does the Pauli Exclusion Principle state?

Answer 1

An orbital can never contain electrons with the same SPIN…

…and the maximum number of electrons that can occupy the same orbital is TWO.

Question 2

What does the Aufbau Principle state?

Answer 2

Electrons occupy the LOWEST energy sublevels available.

(BUS analogy - you would sit in your own seat rather than next to someone else unless the bus is full)

E.G. it is common to see the 1s orbital occupied first, before 3s.

Question 3

What does Hund’s Rule state?

Answer 3

1) Within a sublevel, every orbital is SINGLY occupied before any are doubly occupied…

2) All electrons in singly occupied orbitals have the SAME spin.

E.G. 2p orbital would look like 1 1 1, before ⥮ 1 1, then ⥮ ⥮ 1, then ⥮ ⥮ ⥮.

Question 4

Why is Hund’s rule of “Within a sublevel, every orbital is singly occupied before any are doubly occupied” true?

Answer 4

Because electrons in the same orbital repel each other more than electrons in different orbitals.

And so electrons occupy different orbitals in the same sublevel to reduce repulsion.

Question 5

What are the 3 principles of electron configuration to remember?

Answer 5

Aufbau Principle

Pauli Exclusion Principle

Hund’s Rules