Atomic and molecular orbitals Flashcards
What does the wavefunction squared tell us
the probability of finding an electron
what is an electron density plot
where you draw dots for the shape of the orbital to represent the electrons
what is a boundary surface representation
it is the outline of the electron density plot it enclosed around 95% of the probability of finding an electron
what does the 2 s orbital look like
spherically symmetrical, nucleus at centre, no nodal plane in surface boundary but spherical node
what does the 3s orbital look like
spherically symmetrical, nucleus at centre of sphere, no planar node, 2 spherical nodes
what does a 2p orbital look like
3 identical p orbitals, nodal plane through nuclei, different coloured nodes are different amplitudes of the wavefunction
what does a 3d orbital look like
two nodal planes that intersect at the nuclei except for dz^2 which is 2 nodal cones
what form do orbitals have
ψ=R(r).A(θ,ⱷ)
What does R(r) refer to
the radial wavefunction, how wavefunction varies with distance from nucleus
what does A(θ,ⱷ) refer to
the spherical harmonic, how the wavefunction varies with angle around the nucleus
what are the features of the R(r) and r graphs
when the radial wavefunction hits 0 it is a radial node
an s orbital has a non 0 amplitude at the nucleus, all others are 0 at the nucleus
all orbitals go to 0 at large distances from the nucleus (r)
what does the shading of an orbital mean
relative sign of the wavefunction (its phase) and is important for bond formation
whats an s orbital phase like
spherically symmetrical
boundary surface consistent phase
the phase diagram is like a squared exponential
whats a p orbital phase like
one phase for each lobe
looks like a sin graph with the ends trailing off
what is the quantum number n
principle quantum number, all orbitals with the same value of n belong to the same shell, integer
what is the quantum number l
angular momentum quantum number, same subshell, l determines shape l=0,1…n-1
what is the quantum number ml
magnetic quantum number, individual orbitals, orbital orientation (z is 0)
l,l-1,l-2,0….-l
how does phase bonding work
if the orbital has the same phase, it is a wave, so there is constructive interference which enhances electron density, but if they have different phases, there is destructive interference which means there is 0 probability of the electrons existing there
what happens when atomic orbitals with different phases interact
forms an antibonding mo
forms a nodal plane
has a higher energy level than a bonding orbital due to being destabilised
what happens when atomic orbitals with the same phase interact
lower in E than separate AOs
constructive interference
build up of electron density between the nuclei of the two atoms
what is the aufbau principle
lowest available mo first
what is the pauli principle
max of 2e- in each orbital
opposite spins (ms quantum number =+-0.5)
What is hunds rule
if degenerate orbitals are available they will be occupied individually before the e-s pair up, parallel spins
what is bond order
the number of electrons in bonding mos minus the number of electrons in antibonding mos divided by 2
what does a low bond order number mean
Less stable, weaker bond, longer length, if 0 there is no stable bond
what is the trend of E of aos
E of 2s and 2p go down across period
gap between 2s and 2p increases
energy of 1s goes down sharply after He
if the aos have similar Es they are likely to interact
where does Pz lie
along the internuclear bond (Px is up and py is out of the page)
what are the energy levels comparatively of the p orbitals
Pz are lower, Px and Py are the same
what makes the aos able to overlap to form mos
if they are cylindrically symmetric about the internucleus axis, overlap is possible
Px and Py are not cylindrically symmetric so overlap with the s orbital is not opossible, also the energy requirement
what difference does a heteronuclear diatomic make
different types of orbitals (and sizes) on the two sides of molecule
aos are at different Es so each bonding or antibonding mo is unequally shared between the two atoms
Higher Zeff means
more electronegative
what does a higher Zeff mean for MOs
for sigma electron density more centered on electronegative atom
for sigma star it is more centered on the other atom-different phases remember node
What are the two reasons to be non bonding
lack of overlap (rigorous)
energy mismatch (less rigorous)
How do we check that Mo theory is correct
Photoelectron spectroscopy
what does photoelectron spectroscopy tell us
identity of orbitals
energy of orbitals
what would the results look like
lower energy mo would appear first with the higher signal intensity (intensity of e-)
what molecules show sigma/pi crossover
B2,C2,N2, (Li2, Be2 orbital not fully occupied)
why do some molecules show crossover and not others
due to size of 2s 2p energy gap
for O2 and F2, orbital mixing does occur but not enough for a cross over
what ordering of mos do O2 and F2 have
sigmapz below pipx,py
what ordering of mos do B2 to N2 have
Pipxpy below sigmapz
what ordering of mos do CO and CN have
sp mixing! you can tell by looking at what the homonuclear diatomics do
what ordering of mos in OF
there is no sp mixing
what does paramagnetic mean
drawing into a magnetic field, molecule has unpaired electrons
what does diamagnetic mean
pushed out of a magnetic field, molecule has all of it electrons paired
what are the 4 bond order relationships
-bond enthalpy increases as bond order decreases
-bond distance decreases as bond order increases
-bond enthalpy decreases as bond distance increases
-bond stretching frequency increases as bond order increases
what are isoelectronic species
if they have the same number of electrons
what are some chemical properties of CO
Lewis base-makes it toxic due to it being able to bind to iron centre in haemoglobin more effectively than O2
HOMO c centred lone pair, acts as a donor ligand in complexes
LUMO c centred p* orbital so accepts electrons from transition metal ligands
what does HOMO mean
Highest occupied molecular orbital
what does LUMO mean
Lowest unoccupied molecular orbital
what does it mean if the bond order of a molecule is 0
the molecule is too stable to exist
what is electron affinity
electron attachment
what are the principles of mos
sigma bonds have lower energy than pi
greater the number of nodes the greater the energy
what is a degenerate pair
electron orbitals that have the same energy
