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CHEM 211 > Unit 4 > Flashcards

Unit 4 Flashcards

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1
Q

Red wavelengths?

A

650-700nm

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2
Q

Orange wavelengths?

A

600-650nm

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3
Q

Yellow wavelengths?

A

550-600nm

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4
Q

Green wavelengths?

A

500-550nm

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5
Q

Blue wavelengths?

A

450-500nm

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6
Q

Purple wavelengths?

A

400-450nm

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7
Q

Resonance

A

radiation must have the same energy as a transition between two states

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8
Q

What kind of atomic/molecular transition is involved in UV-visible spectroscopy?

A

transitions of valence electrons

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9
Q

What kind of atomic/molecular transition is involved in infrared spectroscopy?

A

vibration transitions

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10
Q

What are ways in which an atom or molecule can become excited?

A
  • thermal energy
  • absorption of a photon
  • chemical reaction
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11
Q

Between which molecular orbitals do molecules energetically favour excitation?

A

HOMO to LUMO

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12
Q

Ground singlet state (S0)

A
  • totally spin quantum number = 0

- two electrons of opposite spin are in HOMO

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13
Q

1st excited singlet state (S1)

A
  • total spin quantum number = 0

- one electron is located in HOMO and a spin paired electron is in the LUMO

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14
Q

How and why does an excited molecule return to ground state?

A
  • excited state is transient

- via production of heat, light, or energy transfer to another molecule

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15
Q

What are ground state to excited state transition energies dependent on?

A
  • molecular structure
  • intermolecular interactions
  • local environment
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16
Q

Vapour phase

A
  • molecules can rotate and vibrate freely

- vibration and rotational fine structure observed

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17
Q

Dissolved in hexane

A
  • rotational freedom is lost

- collisions with solvent broaden the vibrational transitions

18
Q

Dissolved in water

A
  • stronger interactions with solvent broaden transitions further
  • obliteration of all fine structure
19
Q

Chromophore

A

part of a molecular entity responsible for an absorption band and the approximate location of the corresponding electronic transiition

20
Q

Provide an example of a chromophore

A

-aromatics
-alkenes
-alkynes
-carbonyls
(any unsaturated bonds)

21
Q

What can be done to decrease transition energies?

A

More conjugation of unsaturated bonds

22
Q

Effects of conjugation

A
  • shifts absorption maximum to longer wavelengths

- absorptivity doubles with each conjugated double bond

23
Q

Bathochromic

A

shift to longer wavelength

24
Q

Hypsochromic

A

shift to shorter wavelength

25
Q

Hyperchromic

A

shift to greater absorbance

26
Q

Hypochromic

A

shift to lower absorbance

27
Q

Auxochrome

A

chemical group that is attached to a chromophore and modifies its light absorption properties by altering the energies of the MOs

28
Q

Transmittance

A
  • the ration of the power (P) of the transmitted beam to the incident beam (P0)
  • often expressed as %
29
Q

Absorbance

A
  • negative logarithm of transmittance

- number of orders of magnitude by which transmittance is decreased

30
Q

Blank measurement

A
  • account for non-absorption losses of light

- measured using only the solvent and the same/matched cell

31
Q

Beer-Lambert Law

A

A=EbC (define!)

32
Q

Spectroscopy

A

the study of how physical systems interact with or produce electromagnetic (EM) radiation

33
Q

Spectrometry

A

the measurement of EM radiation to obtain information about systems and their components

34
Q

Spectrophotometry

A

describe measurements made with ultraviolet (UV), visible, and infrared (IR) light

35
Q

Molecular spectrophotometry

A
  • method of molecular analysis

- samples comprise a collection molecules

36
Q

Atomic absorption spectrophotometry

A
  • method of elemental analysis
  • isolated atoms do not usually exist in samples
  • must generate an atomic population with energy input
37
Q

Block diagram of spectrophotometer

A

light source > wavelength selector > sample cell > photodetector > electronics,computer

38
Q

Light sources

A
  • tungsten halogen lamp
  • deuterium lamp
  • light emitting diode
  • laser
39
Q

Wavelength selectors

A
  • diffraction grating
  • prism
  • filters
40
Q

Sample cell

A
  • quartz, glass, plastic

- macro, micro, sub-micro

41
Q

Photodetector

A
  • photomultiplier tube (PMT)
  • photodiode (array)
  • charge-coupled device (CCD)

CHEM 211 (5 decks)

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