6th - molecular orbital energy Flashcards
problem with lewis structure
cannot explain excited states
not all molecular properties can be explained (liquid o2 being blue even tho its said to follow the octet rule)
how can we improve our understanding of chemical bonding
apply wave mechanics
apply the schrodinger equation to multi electron systems
soltuion of molecular schrodinger equation gives
molecular orbitals
what is the diff between atomic and molecular orbitals
molecular orbitals surround the whole molecule
not just the nucleus
molecular orbital probability density
determined by psi squared
where molecular wavefunction is psi
how do we construct molecular orbitals
construct using atomic orbitals using
linea combination of atomic orbitals LCAO
rule for linear combination of atomic orbitals
4 AO gives 4 MO
X AO gives X MO
what approx is linear combination of atomic orbitals based on
that the molecular orbital wavefunction for 2 electrons is the product of two, 1 electron wave functions.
psi MO = psi AO1 x psi AO2
when two atoms come together to form a bond, we must look at the
cross section of their wavefunction.
this cross section is symmetrical
sharp peak shape.
combo of 2 1s orbitals
both in phase is called an
in phase combination
no angular or radial nodes
both phases are +/-
constructive interference, bond will be formed
combo of 2 1s orbitals
in opposite phases
out of phase combination
makes a difference in orbital interaction
destructive interference
different types of wave interference
constructive interference
both in phase, increase amplitude of the wave (same wavefunction signs)
destructive interference
opposite phases, they cancel out
(opposite wavefunction signs)
bonding Mo characteristics
in phase combo of AO
bonding MO
contributes to the bonding interaction of the 2 nuclei
large amount of electron density (large wavefunction value) between the nuclei
M shape with 2hs in the centre with bond connecting them
circle
favourable interaction
antibonding MO characteristics
out of phase combo of AO
antibonding
reduces the bonding interaction between the 2 nuclei
node present at midpoint between the 2 h atoms
unfaourable interaction
2 semi circles with node in the middle
MO energies
bonding MO: most of e- density is between 2nuclei, llows stabilisation due to being attracted to both atom nuclei. lower in energy bc stable
antibonding MO: less e- density between the 2 nuclei. higher in energy, less stable
AO sphere: 50% e- density between 2 nuc, 50% from each AO
