Electron shells and atomic orbitals

Electron shells:

• Formula for the number of electrons each shell can hold 2n^2
• Electrons orbit the nucleus in energy levels or electron shells.
• The energy level is determined by the principal quantum number (n).
• The larger the value for n the further away from the nucleus the shell is and the higher the energy.

Atomic orbitals:

• Only two electrons can ever be in a single orbital
• The two electrons must have opposite spins

The s-orbitals:

• Spherical in shape
• All shells contain an s-orbital
• S-orbitals can hold 2 electrons

The p-orbitals:

• 3D dumbbell shape
• All shells from n=2 upwards contain 3 p-orbitals
• There are three p orbitals px, py and pz

D and f-orbitals:

• 5 d-orbitals (from n=3 upwards)
• 7 f-orbitals (from n=4 upwards)

Filling orbitals:

• Lowest energy orbitals are filled first

• Sub-shells are filled singly first

• When all equal energy sub-shells contain one electron they pair up with another electron with an opposite spin