Electron clouds are 3D, not flat Electrons are spread out as much as possible, not usually round, and are moving rapidly These things are hard to see in a still picture

Electrons spread out in orbitals Orbitals have different SHAPES and ENERGY (distance from nucleus) Quantum numbers describe orbitals There are four quantum numbers

First of the four (n, #, #, #) Describes the distance from the nucleus to the orbital (and therefore describes the ENERGY of the orbital) Values: integers ≥ 1 As the distance from the nucleus increases, n increases. As the energy increases, n increases.

Each period as a unique n value Period 1: n=1 Period 2: n=2 Period 3: n=3 ETC

The transition from n≥2 to n=1in a hydrogen atom Result: ultraviolet emission lines of the hydrogen atom Greater the difference in the principal quantum numbers, the higher the energy of the electromagnetic emission

The transition from n≥3 to n=2 in a hydrogen atom Result: spectral line emissions of the hydrogen atom As the n value increases, the wavelength emitted decreases (in nm) Starting n value Wavelength (nm) ColorRedBlueViolet Ultraviolet

The transition from n≥4 to n=3 in a hydrogen atom Result: emission lines in the infrared band

Second of the four (n, l, #, #) Shape of the sublevel Range from 0 to n-1 (we will never deal with anything above l=3) l=0 = s l=1 = p l=2 = d l=3 = f

Third of the four numbers (#, #, m l, #) Denotes the orbital sublevel that is filled s sublevel has ONE orbital (sphere has one orientation in space) p sublevel has THREE orbitals (three orientations in space) d sublevel has FIVE orbitals (five orientations in space) f sublevel has SEVEN orbitals (seven orientations in space)

s sublevel: one orbital One orientation in space

P sublevels: three orbitals Three orientations in space

d sublevels: five orbitals Five orientations in space

f sublevel: seven orbitals Seven orientations in space

Integers from -l to l SO: s: m l = 0 only since l= 0 p: m l = -1,0,1 since l= 1 d: m l = -2,-1,0,1,2 since l= 2 f: m l = -3,-2,-1,0,1,2,3 since l= 3

Fourth number (#, #, #, m s ) It is either -1/2 or ½ Down or up

There is a very specific order in which electrons fill orbitals. It is not random. There are some exceptions.

1.Aufbau (next) Principle 2.Pauli Exclusion Principle 3.Hund’s Rule

Electrons fill the LOWEST energy sublevel before going to the next sublevel 1s fills, then 2s fills, then 2p fills, then 3s fills, then 3p fills ….

Electrons pair according to OPPOSITE spins ↑↓, not ↑↑ or ↓↓

Electrons spread out in equal energy sublevels before pairing electrons ( ↑ ↑ ↑ and not ↑↓ ↑ _)

First level to fill is 1s level Lowest energy sublevel Holds two electrons They are oppositely paired A sublevel is represented by __ and holds 2 electrons

Second sublevel is the 2s sublevel It holds 2 electrons because of s Electrons are oppositely paired

So, we filled 1s, we filled 2s Now comes 2p Holds six electrons because p orbitals hold 6 electrons 1s 2 2s 2 2p 6

From 2p, 3s fills with 2 electrons 3p fills with 6 electrons 4s fills with 2 electrons 3d fills with 10 electrons 4p fills with 6 electrons 5s fills with 2 electrons

Neutral carbon: 6 electrons ↑↓ ↑↓ ↑ ↑ _ 1s 2s 2p Six arrows for six electrons 1s 2 2s 2 2p 2

Some energy levels are SUPER close together The levels are so close that electrons are able to move between these orbitals in order to minimize repulsion… 4s and 3d orbitals are very close in energy Exceptions exist for some period 4 d block elements Cr is not 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 Cr is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 It actually takes LESS energy to split the electrons between the 5 sublevels than it does to put them together in the 4s and 3d