Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Chemistry Of The Elements > Magnetic and spectral properties of TM properties > Flashcards

Magnetic and spectral properties of TM properties Flashcards

1
Q

Singlet

A

spins of electrons are in different directions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Triplet

A

spins of electrons are in the same direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Selection rules for electron transitions

A

the selection rules tell us about the probability of a transition and hence the intensity of the resulting band in the spectrum

  • spin selection rule: ΔS = 0
  • laporte selection rule: a change in parity is required, since a photon has angular momentum
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Approximate wavelength ranges of the different colours (nm)

A

red: 700-620
orange: 620-580
yellow: 580-560
green: 560-490
blue: 490-430
violet: 430-380

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why are electronic spectra bands broadened?

A

spectra are broadened through the effects of molecular vibrations and rotations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Molar extinction coefficient, ε

A

the proportionality constant: how intrinsically intense the absorption is (can be defined at any wavelength)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What do ⫪-donor ligands do to Δ o ?

A

small Δ o

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What do ⫪-acceptor ligands do to Δ o ?

A

large Δ o

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the energy of transitions for d 1 , d 4 (high-spin), d 6 (high-spin), and d 9 ?

A

the energy of the transition is equal to Δ o

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the energy of transitions for d 2 , d 3 , d 7 (high spin) and d 8 ?

A

complexes of these ions show more than one band - usually two or three - of very different energies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What do electron-electron repulsions depend on?

A

they depend on the arrangement of the electrons in the different d orbitals and on their spin
(repulsion is different according to which d orbitals the electrons occupy).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Russell-Saunders coupling scheme

A

spin-spin: coupling of spin angular momenta of electrons
→ S then 2S+1

orbit-orbit: coupling of orbital angular momenta
→ L

spin-orbit: coupling of the spin and orbital angular momenta
→ J
(only a small effect for 1st row TM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Term symbol

A

a kind of ‘shorthand’ describing the energy, angular momentum and spin multiplicity of an atom in any state

(Different terms have different energies)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How to identify lowest-energy states using Hund’s Rules

A
  1. The ground state has the largest spin multiplicity (2S+1)
  2. If two terms have the same spin multiplicity, the term with the larger value of L is the lowest in energy
  3. For <1/2 filled subshell, ground state has lowest J and vice versa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the “weak-field approach”?

A

it assumes that the effect of the ligand field splitting is substantially less than that of interelectronic repulsion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the “strong-field approach”?

A

where the ligand field splitting is assumed to be much larger than the interelectronic repulsion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What do orgel diagrams show?

A

the effect of ligand field on the relative energies of the terms

(energy v splitting plots)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Requirements for orgel diagrams

A
  • High-spin cases only
  • Spin-allowed transitions only (i.e. only those states having the same spin multiplicity as the ground state are included - except for d 5 as none are spin-allowed)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is an electron hole?

A

a single electron in an empty d-orbital
(same as a +ve charge in a filled d-shell)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are term symbols used for in spectroscopy?

A

To describe the electronic states of atoms or ions based on total spin (S), orbital angular momentum (L), and total angular momentum (J).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the spin multiplicity of a singlet state?

A

1 (i.e. 2S+1=1, so S=0)

22
Q

How do you determine the ground term symbol?

A

Use Hund’s rules:
- Maximum spin
- Then maximum L
- For < 1/2 filled subshell, lowest J
- For >1/2 filled subshell, highest J

23
Q

What do Orgel diagrams represent?

A

Orgel diagrams show the energy levels of high-spin d-electron configurations in weak field ligands

24
Q

For which d-electron configurations are Orgel diagrams useful?

A

Mostly for d 1 to d 7 in high-spin complexes since d 8 and d 9 are too complex

25
What is the difference between Orgel and Tanabe-Sugano diagrams?
Orgel diagrams are qualitative and only for high-spin. Tanabe-Sugano diagrams handle both high- and low- spin and give quantitative splitting.
26
What determines the relative energy levels in an Orgel diagram?
Electron–electron repulsion and the crystal field splitting from ligands
27
What transitions are shown in Orgel diagrams?
Only spin-allowed transitions
28
What do Tanabe-Sugano diagrams show?
they plot the energy levels of electronic states for a specific d n configuration as a function of ligand field strength (Δ o
29
What is B and what does it measure?
B = the "Racah" parameter It measures repulsion of terms of the same multiplicity
30
How does the Racah parameter vary from free ions to complexes?
B is often reduced in complexes from the free ion value due to covalency (e.g. pairing energies are lower in complexes)
31
What is the Nephelauxetic effect?
the reduction in interelectronic repulsion between d-electrons of a transition metal when it forms a coordination complex
32
Why does the Nephelauxetic effect occur?
Ligands allow the d-electrons to delocalise more, which spreads out their charge, reducing repulsion
33
When are bandwidths likely to be broad?
when the gradient of the ground state and excited states on Orgel/ Tanabe-Sugano diagram are very different from one another as it means the magnitude of E is very sensitive to small changes in Δ and therefore to vibrations
34
Why can transitions occur in octahedral complexes when electronically forbidden?
if the transition is vibronically allowed
35
Why are there stronger absorption of tetrahedral vs octahedral?
p-d mixing in tetrahedral complexes relaxes the Laporte selection rule (p and d orbitals have the same symmetry)
36
How is the spin selection rule relaxed?
By spin-orbit coupling (a spin-forbidden transition may be observed if it has similar energy to a spin-allowed transition)
37
Why do first-row transition metal d-d states not emit light?
They absorb light instead because an electronic excited state energy may be converted into vibrational energy on a timescale of 1 picosecond (10 -12 s) which is much faster than for the emission of a photon.
38
Why do charge-transfer transitions tend to have higher intensity absorptions?
the Laporte selection rule doesn't apply
39
How can LMCT be interpreted?
- Flow of charge - Oxidation of the ligand, reduction of the metal - Process occurs within the timescale of absorption of a photon by the complex (~10 -16 s) - Rapid charge recombination (once the charge is transferred, there is a large thermodynamic driving force for the charge to return to its groundstate - these states don't last long)
40
What metals favour LMCT?
metals in high oxidation states
41
LMCT in tetrahedral d 0 complexes
MnO 4 - intense purple Cr 2 O 4 2- intense yellow Cr 2 O 7 2- (acidified chromate solution) intense orange
42
What metals favour MLCT?
Metals in low oxidation state (relatively easy to oxidise)
43
What is the energy of MLCT related to?
- the ease of oxidation of the metal - the ease of reduction of the ligand
44
Requirements of MLCT
- Likely to occur at low energy - Requires metal to be in low oxidation state - Requires ligands to have low-lying acceptor orbitals, usually ⫪*
45
What technique gives direct experimental evidence of MLCT?
Time-resolved infrared spectroscopy (TRIR)
46
How does time-resolved infrared spectroscopy (TRIR) work?
IR absorption spectroscopy of a molecule while in its electronically excited state. The IR stretches of reporter groups, such as the C=O group of esters, shift to lower frequencies in the excited state, indicating a weakening of the C=O bond due to the partial population of the ⫪* orbital.
47
What are the main classes of bulk magnetism?
1. Diamagnetism 2. Paramagnetism 3. Ferromagnetism 4. Ferrimagnetism
48
Diamagnetism
- Exhibited in substances with paired electrons - Application of external magnetic field causes a 'distortion' of the electronic orbital currents (i.e. the sample is repelled against the applied field)
49
Paramagnetism
- Exhibited in substances with unpaired electrons - It is caused by the circulation of unpaired electrons (generates a magnetic field directed with the applied field) -Expressed as the magnetic moment (𝜇)
50
When can orbital contribution to 𝜇 occur?
If it is possible to transform the orbital occupied by an unpaired electron into an equivalent orbital by rotation around the direction of the applied field. This means spin-only formula cannot be used.
51
When is orbital contribution expected?
if the ground-state term has T symmetry but NOT if E or A symmetry
52

Chemistry Of The Elements (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions