Molecular orbitals Flashcards
What is sp2 hybridisation?
Mixing an s orbital with two p orbitals
What is hybridisation?
The process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals. These hybrid orbitals are degenerate
How is a sigma bond formed?
end on overlap of orbitals
How is a pi bond formed?
Side on overlap of orbitals
What allows colour?
Conjugated system
A single bond has
only sigma bonds
A double bond has
1 pi bond 1 sigma bond
A triple bond has
2 pi bonds 1 sigma bond
sp3
single bond
sp2
double bond
sp
triple bond
What kind of hybridisation do benzene and other aromatic groups have?
sp2
Electrons fill bonding molecular orbitals, leaving higher
HOMO/LUMO
energy antibonding orbitals unfilled
The highest bonding molecular orbital containing electrons is called
HOMO/LUMO
The highest occupied molecular orbital (HOMO)
The lowest antibonding molecular orbital is called
HOMO/LUMO
the lowest unoccupied molecular orbital (LUMO)
What can cause electrons to be promoted from HOMO to LUMO?
HOMO/LUMO
Absorption of electromagnetic energy
Why do most organic molecules appear colourless?
HOMO/LUMO
because the energy difference in HOMO and LUMO is relatively large. This results in absorption of light from the ultraviolet region of the spectrum
Some organic molecules contain…
HOMO/LUMO
chromophores
What is a chromophore?
HOMO/LUMO
A group of atoms within a molecule that is responsible for the absorption of light in the visible region of the spectrum
When can light be absorbed in a molecule?
HOMO/LUMO
When electrons in a chromophore are promoted from the HOMO to the LUMO
In what type of molecules do chromophores exist?
HOMO/LUMO
molecules containing a conjugated system
Electrons within a conjugated system are
HOMO/LUMO
delocalised
Molecules that have a conjugated system have alternating
double and single carbon to carbon bonds (or are aromatic molecules)
The more atoms in a conjugated system the
HOMO/LUMO
smaller the energy gap between HOMO and LUMO
