1.4 Sub-shells & Atomic Orbitals

What is a sub-shell?

A division of a principal energy level (shell) where electrons occupy regions of similar energy (s, p, d sub-levels).

What are the sub-shell types?

s, p, and d (in increasing energy within a shell).

How many electrons can each sub-shell hold?

• s = 2

• p = 6

• d = 10

What is an atomic orbital?

A region in space around the nucleus where there is a high probability of finding an electron.

How many electrons can one orbital hold?

A maximum of 2 electrons (with opposite spins).

How many orbitals are in each sub-shell?

• s = 1 orbital

• p = 3 orbitals

• d = 5 orbitals

What is the shape of an s orbital?

Spherical (around the nucleus).

What is the shape of p orbitals?

Dumbbell (hourglass-shaped) with three orientations: px, py, pz.

What is the difference between shells and sub-shells?

Shells are main energy levels (n = 1, 2, 3…), while sub-shells are divisions within shells (s, p, d).

What is electronic configuration?

The arrangement of electrons in shells and sub-shells of an atom.

What rule is used to fill electron sub-shells?

Electrons fill lower energy sub-shells first (Aufbau principle).

What is the correct filling order of sub-shells?

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s…

Why is 4s filled before 3d?

Because 4s is lower in energy than 3d in the ground state.

How do you write electronic configuration?

Write sub-shells in order and show number of electrons as superscripts (e.g. 1s² 2s² 2p⁶).

Example electronic configuration of sodium (Na, Z=11)?

1s² 2s² 2p⁶ 3s¹

What happens to electrons when ions form?

Electrons are lost or gained from the outermost sub-shell.

Electronic configuration of Mg²⁺?

1s² 2s² 2p⁶

Electronic configuration of N³⁻?

1s² 2s² 2p⁶

What is a key feature of orbitals?

Each orbital can hold a maximum of 2 electrons with opposite spins.

What is the main idea of sub-shell energy levels?

Sub-shells have different energies even within the same shell (s < p < d).