lecture 7

Question 1

atomic spec can also be called ,,, and what is seen

Answer 1

electronic spec

u can only see changes to do with electrons

Question 2

when we change the state of an atom what do we also change

Answer 2

when we change the state of an atom,, we change its wavefunction!!!

think about all the steps we did : splitting it into radial and angular wave functions: if we change the first bit,, the wavefunction will also change.

Question 3

if wavefunction changes when u change the position of an e-. ,, and in electronic//atomic spec we interact an atom with a photon of light to change its position,, what different wavefunctions will we have

Answer 3

we will have an initial wavefunction: before the e- moving // transitioning due to absorbtion of a photon.
Y.i

and we will also have a final wavefunction,, this is the wavefunction after the atom has interacted with the photon of light. and has moved from its original place. Y.f

Question 4

gross selection rule for atomic // electronic spec

Answer 4

there must be a change in the dipole moment between the initial and final states.

Question 5

what can symmetry do

Answer 5

symmetry can predict if the whether the transition dipole is non zero

Question 6

initial and final wavefunctions of H

Answer 6

1s
2s
2p

Question 7

initial wavefunction is all about

Answer 7

n, l , ml

aka if we have a 1s 2s 2p etc orbital

Question 8

specific selection rule of atomic//electronic spec

Answer 8

describes the allowed transitions between states

shows what changes are allowed when things abs//emit photons of light

more focused on graphs whereas the gross selection rule is more focussed on the atom itself

Question 9

emission

Answer 9

lose photon

lose energy via a photon

Question 10

absorption

Answer 10

gain energy by absorbing a photon of light

Question 11

describe a photon and what quantum numbers it has

Answer 11

photon = one bit of light

it has a mass of 0
it has a spin of 0
it has an angular momentum of 1
l = 1

Question 12

what is conservation of angular momentum

Answer 12

when the angular momentum of the atom and light (photon) interact + act together

they conserve momentum between the initial and final wavefunctions.

Question 13

what transitions can and cant occur

Answer 13

only transitions that conserve angular momentum between initial and final are allowed!!

Question 14

for Hydrogen: write down the transition rules

Answer 14

change in l = +- l
change in ml = 0, +-1

change in n doesnt matter as long as l and ml dont change!!!

Question 15

what does the selection rule: change in l = +- 1 mean

Answer 15

that u can have transitions between
s -> p
p -> d
but u cant have an s -> s transition!!

think of the energy level diagram with energy on the y axid and l values on the x axis.

Question 16

on the energy level diagram of energy on the y and l value on the x,, what are the ml’s seen as

Answer 16

okay so for 2p
u have 3 different lines
theyre ml: -1 0 +1

those are whwat we mean by ml

Question 17

so if ur allowed a change of l +- 1,, what does this mean

Answer 17

where the line is of the initial e- position,, u can either move to the right or to the left but only by 1.

and same with ml values,, for s the ml = 0

so make sure u label ur graph fully so yk whats going on 💗 and remember that change in the n value doesnt matter if l = +-1 and ml = 0, +-1

Question 18

the labelled energy diagram with all the lines of the allowed transitions is called a

Answer 18

gotrian diagram

the thicker the lines: the more of that transition there issssss.

Question 19

okay so the H electron is special bc we only ever need to think of 1 e-,, and this can be described using what quantum numbers

Answer 19

n , l , ml

dont even need ms bc its 1/2

Question 20

okay but for He and for other atoms,, there are more than 1e- so what quantum numbers are used to describe them

Answer 20

we need the L, S, and J quantum numbers

bc these describe the whole atom,, not just 1e-,, they include all the e-!!!

Question 21

so the grotrian diagram for multielectron systems will include what difference to the normal H one.

Answer 21

the normal H one doesnt have J values and so theyre energy diagram isnt split into low and high energy.

bu for other atoms,, there is a J value,, and we need to show the higher and lower energy line splits!!! also label these bc it makes life sm easier once we think about the allowed transitions and selectrion rules!!

Question 22

okay so for a multielectron system :what rules are there and explain themmmm

Answer 22

change in J: 0, +-1
change in L: 0, +-1
change in S: 0!!

J when energy levels are split make sure u labels them using the 3/2 1/2 and 5/2 3/2 bc it makes this sm easier to do!!

for L = 0, +-1
remmeber that small l values can change,, but it may leave the L unaffected. L means u can move right / left

also its kinda easier if u draw the orbitals on top of eachother: so like the 4d ones directly above the 3p ones and draw arrows coming down that way: its easier to see the different j level changes

Question 23

if theres 3 different possible transitions,, what is there in emission spec

Answer 23

3 transition that lead to emissions gives u 3 lines in emission speccccc

Question 24

what is the multiplicity equation again

Answer 24

2S+1

u get a singlet,, doublet,, triplet etcccccc

u still need to respect pauli aswell tho

Question 25

so for He,, what is the multiplicity

Answer 25

1s2 ground state

and they cancel out bc theyre antiparallel

to give s=0

so then 2 x 0 + 1 = 1 so its a singlet

Question 26

He excited state multiplicity

Answer 26

1s1 2s1 same spin
add them = 1
2 x 1 + 1 = 3 triplet state
lower energy arrangement due to spin pair energy!!!!

1s1 2s1 but opp spins = cacel to give s = 0
and then 2 x 0 + 1 to give 1 so another singlet!!! but this is the higher energy arrangement

Question 27

why is a He triplet state lower energy than the He single stage

Answer 27

it’s lower in energy bc it’s spin pairing energy!!

bc they have the same spin (both going anti clock // clockwise)

Question 28

can u go from a singlet to a triplet state

Answer 28

nope

bc change in S = 0
and S in singlet is 0
and S in triplet is 1
so this would give a change in 1

Question 29

if change in S can’t change and has to be 0,, what happens when an atom,, like He,, has a singlet (s=0) and a triplet (s=1) state

Answer 29

u would see 2 different spectra

one for each spin state.

and each spin state will contain its transitions in its own spin state part

Question 30

fine structure due to spin orbit coupling: what do we see

Answer 30

we see how the orbitals in different shells are split into low and higher energy

Question 31

what differences in spectra does fine structure give

Answer 31

it gives 2 lines!!!
and the cm-1 between the lines is based on the atoms Z (nuc charge)

larger Z = larger angular momentum!!
so larger atoms will have a larger cm-1 value!!!

Question 32

for change in J being restricted to 0 or +-1 what’s an easier was to check this and see how many peaks are in emission spec

Answer 32

u draw the 4d split orbitals and the 3p split orbitals directly above one another and label the splits with their number (5/2 3/2) (3/2 1/2) then draw a line to where the e- is allowed to transition to based on J values.

the amount of lines u have is the amount of peaks ur emission spec will have.

Question 33

wavefunction strategy in atomic spec

Answer 33

okay so atomic spec causes a change in electrons : from where it initially is to where it finally will end up.

so a change in the atom = change in Y = Yi + Yf