1. Electronic Structure

Shells

• Energy levels - it increases as the shell number increases (shell number - principal quantum number n)

n = 1

• 2 electrons

n = 2

• 8 electrons

n = 3

• 18 electrons

n = 4

• 32 electrons

Formula for the maximum number of electrons in shell (n)

• 2n² 

Atomic orbitals

• A region around the nucleus that can hold up to 2 electrons with opposite spins

S-orbitals

• Spherical shape

• n = 1 has 1 s-orbital (sub-shell 2)

• The greater the shell number (n), the greater the radius of the s-orbital

P-orbital

• Dumb-bell shape

• n = 2 has 3 p-orbitals (sub-shell 6)

• The greater the shell number (n), the further the p-orbital is from the nucleus

D-orbital

• More complex

• n = 3 has 5 d-orbitals (sub-shell 10)

F-orbital

• More complex

• n = 4 has 7 f-orbitals (sub-shell 14)

n = 1 order of filling

• 1s (2)

n = 2 shell order of filling

• 2s (2), 2p (6)

n = 3 order of filling

• 3s (2), 3p (6), 3d (10)

• However, 3d has a higher energy level than 4s so 4s goes first

n = 4 order of filling

• 4s (2), 4p (6), 4d (8), 4f (14)

Electrons-in-box model - explanation

• Electrons are negatively charged and they repel one another

• They have a property called spin (up or down)

• They must have opposite spins to counteract the repulsion between the negative charges

Orbitals with the same energy level

• One electron has to occupy each orbital before pairing starts

• This prevents any repulsion between paired electrons until there is no further orbital available

Exceptions for 3d before 4s

• Copper and Chromium

Simplified version of the Electronic Configuration

• Find the noble gas which fills up closest to the configuration (it must be lower)

Blocks in the Periodic Table

• S-Block - group 1 and 2

• P-Block - group 3, 4, 5, 6, 7, 8

• D-Block - middle table