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Chemistry sem 1 > Atomic and molecular orbitals > Flashcards

Atomic and molecular orbitals Flashcards

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1
Q

What does the wavefunction squared tell us

A

the probability of finding an electron

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2
Q

what is an electron density plot

A

where you draw dots for the shape of the orbital to represent the electrons

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3
Q

what is a boundary surface representation

A

it is the outline of the electron density plot it enclosed around 95% of the probability of finding an electron

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4
Q

what does the 2 s orbital look like

A

spherically symmetrical, nucleus at centre, no nodal plane in surface boundary but spherical node

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5
Q

what does the 3s orbital look like

A

spherically symmetrical, nucleus at centre of sphere, no planar node, 2 spherical nodes

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6
Q

what does a 2p orbital look like

A

3 identical p orbitals, nodal plane through nuclei, different coloured nodes are different amplitudes of the wavefunction

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7
Q

what does a 3d orbital look like

A

two nodal planes that intersect at the nuclei except for dz^2 which is 2 nodal cones

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8
Q

what form do orbitals have

A

ψ=R(r).A(θ,ⱷ)

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9
Q

What does R(r) refer to

A

the radial wavefunction, how wavefunction varies with distance from nucleus

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10
Q

what does A(θ,ⱷ) refer to

A

the spherical harmonic, how the wavefunction varies with angle around the nucleus

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11
Q

what are the features of the R(r) and r graphs

A

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)

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12
Q

what does the shading of an orbital mean

A

relative sign of the wavefunction (its phase) and is important for bond formation

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13
Q

whats an s orbital phase like

A

spherically symmetrical
boundary surface consistent phase
the phase diagram is like a squared exponential

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14
Q

whats a p orbital phase like

A

one phase for each lobe
looks like a sin graph with the ends trailing off

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15
Q

what is the quantum number n

A

principle quantum number, all orbitals with the same value of n belong to the same shell, integer

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16
Q

what is the quantum number l

A

angular momentum quantum number, same subshell, l determines shape l=0,1…n-1

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17
Q

what is the quantum number ml

A

magnetic quantum number, individual orbitals, orbital orientation (z is 0)
l,l-1,l-2,0….-l

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18
Q

how does phase bonding work

A

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

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19
Q

what happens when atomic orbitals with different phases interact

A

forms an antibonding mo
forms a nodal plane
has a higher energy level than a bonding orbital due to being destabilised

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20
Q

what happens when atomic orbitals with the same phase interact

A

lower in E than separate AOs
constructive interference
build up of electron density between the nuclei of the two atoms

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21
Q

what is the aufbau principle

A

lowest available mo first

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22
Q

what is the pauli principle

A

max of 2e- in each orbital
opposite spins (ms quantum number =+-0.5)

23
Q

What is hunds rule

A

if degenerate orbitals are available they will be occupied individually before the e-s pair up, parallel spins

24
Q

what is bond order

A

the number of electrons in bonding mos minus the number of electrons in antibonding mos divided by 2

25
Q

what does a low bond order number mean

A

Less stable, weaker bond, longer length, if 0 there is no stable bond

26
Q

what is the trend of E of aos

A

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

27
Q

where does Pz lie

A

along the internuclear bond (Px is up and py is out of the page)

28
Q

what are the energy levels comparatively of the p orbitals

A

Pz are lower, Px and Py are the same

29
Q

what makes the aos able to overlap to form mos

A

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

30
Q

what difference does a heteronuclear diatomic make

A

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

31
Q

Higher Zeff means

A

more electronegative

32
Q

what does a higher Zeff mean for MOs

A

for sigma electron density more centered on electronegative atom
for sigma star it is more centered on the other atom-different phases remember node

33
Q

What are the two reasons to be non bonding

A

lack of overlap (rigorous)
energy mismatch (less rigorous)

34
Q

How do we check that Mo theory is correct

A

Photoelectron spectroscopy

35
Q

what does photoelectron spectroscopy tell us

A

identity of orbitals
energy of orbitals

36
Q

what would the results look like

A

lower energy mo would appear first with the higher signal intensity (intensity of e-)

37
Q

what molecules show sigma/pi crossover

A

B2,C2,N2, (Li2, Be2 orbital not fully occupied)

38
Q

why do some molecules show crossover and not others

A

due to size of 2s 2p energy gap
for O2 and F2, orbital mixing does occur but not enough for a cross over

39
Q

what ordering of mos do O2 and F2 have

A

sigmapz below pipx,py

40
Q

what ordering of mos do B2 to N2 have

A

Pipxpy below sigmapz

41
Q

what ordering of mos do CO and CN have

A

sp mixing! you can tell by looking at what the homonuclear diatomics do

42
Q

what ordering of mos in OF

A

there is no sp mixing

43
Q

what does paramagnetic mean

A

drawing into a magnetic field, molecule has unpaired electrons

44
Q

what does diamagnetic mean

A

pushed out of a magnetic field, molecule has all of it electrons paired

45
Q

what are the 4 bond order relationships

A

-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

46
Q

what are isoelectronic species

A

if they have the same number of electrons

47
Q

what are some chemical properties of CO

A

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

48
Q

what does HOMO mean

A

Highest occupied molecular orbital

49
Q

what does LUMO mean

A

Lowest unoccupied molecular orbital

50
Q

what does it mean if the bond order of a molecule is 0

A

the molecule is too stable to exist

51
Q

what is electron affinity

A

electron attachment

52
Q

what are the principles of mos

A

sigma bonds have lower energy than pi
greater the number of nodes the greater the energy

53
Q

what is a degenerate pair

A

electron orbitals that have the same energy

Chemistry sem 1 (3 decks)

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