Unit 4 Orbitals

Angular nodes

Straight cut across, touches the center

Radial node

Circular cut

sp3 hybrid

Use for tetrahedral molecules (109.5 degrees)

sp2 hybrid

use for trigonal molecules (120 degrees)

sp hybrid

use for linear molecules (180 degrees)

Hybrid structure/drawing

pointy shaded bits point towards the middle, bulbous unshaded parts on the outskirts

Amplitude determines…

total amount of energy in a wave. Bigger amplitude = more power

Wavelength of light determines

How much energy an individual molecule is able to grab out of light at one time

Light is quantized into fixed-sized pieces called

photons

Ephoton =

hc/wavelength = hv (frequency)

Intensity of light

The number of photons

More nodes means

shorter wavelength, more energy

To eject more electrons from a sample…

Make the light brighter

How to tell which element’s ionization energy is higher? How to tell which molecule’s energy is higher.

Element IE is higher as the radius gets smaller. Molecule IE is higher if its highest energy orbitals are bonding rather than antibonding.

How to tell which molecule donates (HOMO) and which accepts (LUMO) in electron transfer

The donor is the species with the higher-energy HOMO. The acceptor is the species with the lower-energy LUMO.

MO diagram rule

For B, C, & N, pi 2p is lower energy than sigma 2p

For O, F, Ne, sigma 2p is lower energy than pi 2p

Only consider valence electrons when filling it in and writing the orbital types

How to tell if electron lone pair is in a p orbital/delocalized

Leftover p orbitals form delocalized pi bonds in large molecules

If the atom its attached to is sp2 and next to a pi bond or part of a ring.

If electrons can be moved to make a resonance structure, electrons are delocalized.

Higher energy light means

larger energy gap

Lower energy light means

smaller energy gap

Removing a proton can sometimes allow more atomic orbitals to combine into MOs because

A lone pair may be created or become available, and it can participate in conjugation, allowing more MOs to be formed

sp hybridization, how many unhybridized p orbitals remain

2 p orbitals

sp2 hybridization, how many unhybridized p orbitals remain

1 p orbital

sp3 hybridization, how many unhybridized p orbitals remain

0 p orbitals

Find number of photons

Total energy/Energyphoton (Get from plugging wavelength into formula)

If the removed electron comes from an anti-bonding orbital

the bond order will increase by 0.5, and the bond attraction (strength) will increase

If the removed electron comes from a bonding orbital

the bond order will decrease by 0.5, and the bond attraction (strength) will decrease.

weaker bonds are

longer bonds

If highest energy orbitals are antibonding…

easier to ionize than bonding orbitals, lower ionization energy

Atomic orbitals

• ΔE > 0:

• absorption

• ΔE < 0:

emission

The more atoms involved in the extended 𝜋 system

the smaller the change in the electron “wavelength” in the HOMO-to-LUMO transition. 

Pi bonds always use

pure p orbitals

More protons =

stronger pull, higher IE

Larger radius =

weaker pull, lower IE

More core electrons =

less pull on outer electrons = lower IE

Electrons become excited by

absorbing energy from light/surroundings

Electrons are ejected/ionized when

it gains enough energy from light to overcome the attractive forces holding it to an atom