Formal Charge & Molecular Orbital Theory - Orgo Chem

What is formal charge?

the charge of an atom or molecule assuming that all of the bonds are 100% covalent

Formal charge formula

#VE - (#NBE + ½ Bonding E)

Carbocation

carbon atom with a positive formal charge

Carbanions

carbons with a negative formal charge

Usually, what is the formal charge of a H atom that has 1 bond

usually 0

What is the Molecular Orbital Theory?

describes that electrons can be found in orbitals belonging to the entire molecule including in phase and out of phase

• describes that electrons move from filled to empty orbitals

• stronger than VB theory

What does LCAO mean?

Linear Combination of Atomic Orbitals: combining orbitals both in and out of phase

Connective interference (in phase)

when electrons are attracted to the positive nuclei causing orbital overlap (sigma bonding)

Destructive interference

when electrons move away from the positive nuclei (antibonding)

What is a node line? When is it used?

node line is an area of a molecule where there is 0% chance of finding an electron; used to represent an antibonding orbital

Higher energy = ..

less stable (electrons are farther from the positive nucleus)

Lower energy =

more stable (b/c electrons are closer to positive nucleus)

What are the frontier molecular orbitals?

includes LUMO and HOMO which represents the orbitals chemical reactivity

What is LUMO in an energy diagram?

Lowest Unoccupied Molecular Orbital- contains no electrons, less stable, and higher in energy diagram

What is HOMO in an energy diagram?

Highest Occupied Molecular Orbital- contains electrons, more stable, and lower in energy diagram

HOMO-LUMO Gap

the difference in energy

electrons always fill the .(blank) orbitals first

lowest energy