105 Lecture 1 – Flashcards
Unlock all answers in this set
Unlock answers| what is spectroscopy? |
| the study of the interaction of matter with electromagnetic radiation |
| what is infra-red spectoscopy used to identify? |
| functional groups |
| what is Nuclear Magnetic Resonance Spectroscopy used to identify? |
| the CH framework |
| what is ultra-violet and Visible Spectroscopy used for? |
| to identify the ? system |
| what is mass spectroscopy used to identify? |
| the mass and formula |
| what is electromagnetic radiation? |
| it is light that is composed of oscillating electric and magnetic fields that transmit energy through space |
| in relation to the direction of propagation which axis would you find the electric and the magnetic field? |
electric field on Y axis
magnetic field on X axis |
| why cannot light always be modelled as simply a wave? |
because of wave partical duality
|
| what are particles of electromagnetic radiation called? |
photons
the energy (E) of a photon is related to the wave properties of
|
| the distance between succesive crests is known as the..... |
wavelength
symbol give : lamba
measured in metres |
| waves per second is known as...... |
frequency
symbol given: V measured in cycles per second = Hz |
| waves per metre as a unit length is known as..... |
wavenumber
symbol given: V with a line on top. measured in metres-1 |
2.998 x 108 m-1 is which constant? |
the speed of light baby!
it is given the symbol C |
6.63 x 10-34 Js is which constant? |
is it plancks constant
it is given the symbol 'h' |
| if you were given the frequency, how would you work out the energy of a photon? |
E = hv
E = plancks constant x frequency |
| if you were given the wavelength how would you work out the energy of a photon? |
E = hc/?
E= plancks x speed of light / wavelength |
| if you were given the wavenumber, how would you work out the energy of a photon? |
E = hcv-
E= plancks x speed of light x wavenumber |
| how to work out frequency ? |
v = c/?
frequency = speed of light / wavelength |
| how to work out wavenumber? |
v- = 1/?
wavenumber = 1/wavelength |
photons from different regions of the spectrum have very different energies - their wavelengths and frequencies vary according.
name the electro magnetic spectrum from highest energy to the lowest energy (7) |
gamma rays, xrays, UV, visible, Infra-red, microwave, radiowave
low energy radiowaves have longer wavelengths that high energy gamma rays |
| what wavelengths does visible light have? |
400-700nm
red light has a longer wavelength and lower energy than blue light |
103 Hz is how many kHz? 106 Hz is how many MHz? 109 Hz is how many GHz? |
103 Hz is 1 kHz 106 Hz is 1 MHz? 109 Hz is 1 GHz? |
| when light of a particular wavelength passes into a substance what are the two possible outcomes? |
1. no photons are absorbed - the substance transmits light of that wavelength
2. some or all of the photons are absorbed - molecules in the sample take up energy |
| if absorbtion occurs, what happens to the energy? |
it is always conserved
hence when a photon is absorbed the molecule undergoes an energy change that is equal to the energy of the photon. |
true or false? a molecule can be partially absorbed by a photon? |
False
a molecule CANNOT be partially absorbed by a photon; It s an all or nothing event |
| what must a photons energy be in order for it to be absorbed? |
its energy must be exactly equal the energy difference between the old and the new molecular energy states.
the same applies to the emission of a photon when a molecule in an excited state moves to a lower energy state |
| name the two types of molecular energy |
internal energy translational energy |
| define internal energy |
energy stored within a molecule from the result of its rotation, vibration or electrical distribution
|
| define translational energy |
this is the motion of the whole molecule through space translational energy cannot normally couple with electromagnetic radiation. changes in trasnlational energy result only from collisions between molecules |
true or false? translational energy can be coupled with electromagnetic radiation? |
false
translational energy cannot normally couple with electromagnetic radiation. changes in translation energy result from collisions between molecules. |
name the 3 ways internal energy can be classified according to how it is stored
these forms of energy are quantised what does this mean? |
rotational energy vibrational energy electronic energy
quantised means that the molecules can only lose or gain certain 'well defined' amounts of internal energy. it cannot gain or lose arbitary amounts
|
the approx energy gap between Rotational energy levels is:
?E ~10-19 - 10-22 J
which region of the electromagnetic spectrum has energies in this range? |
Microwave region have energy in this range
? 1- 10-3 m |
| when i say rotational energy which region should pop into your head? |
| microwave region |
vibrational energy levels ~ 10-19 - 10-22 J
which region has energies in this range? |
Infra red
when say vibrational energy you should think infra red |
| electronic energy levels are related to which region of the electromagnetic spectrum? |
| UV/ visible light photons |
here is a easy thing to help you remember the molecular energy levels and their relationship to the elctro magnetic spectrum
EU MR IV |
Electronic energy - UV/visible photons
Microwave photons - Rotational energy
Infra-red photons - Vibrational energy |
| what do the energy seperations between different quantum levels depend on? |
| they depend on the molecular structure |
| name the 4 common features of absorbtion spectrometers |
a radiation source a sample cell a dispersion element a light intensity detector
modern spectrometers use a beam splitter thater than a dispersion device and all wavelengths are collected simultaneously. this > speed and sensitivity |
what does an absorbtion spectrum show?
|
how much light has been absorbed by the sample as a function of the wavelength of the light.
the amount of light absorbed at each wavelength is usually displayed as absorbance (A)
|
| what kind of scale is absorbance measured in? |
a logarithmic scale
no light absorbed? = absorbance 0 90% light absorbed? = absorbance 1 99% light absorbec? = absorbance 2 etc |
in IR spectra what is commonly used instead of absorbance?
what affect does this have on the graph peaks? |
% transmittance is used more commonly that absorbance
this is the % of incident light passing through the sample
the absorbtion peaks are inverted when showing transmission |
the internal energy states of molecules are .......... in ways that depend on the structure of the molecule
........ gives direct information about the energy seperation between these molecular states because a ....... can only be absorbed if it has ..... the right energy to excite the molecule to a higher .......... energy state. Hence ........ information can be deduced from the energies of the photons that a molecule........... |
quantized, spectroscopy, photon, exactly, internal, stuctural, absorbs
the internal energy states of molecules are quantised in ways that depend on the structure of the molecule. Spectroscopy gives direct information about the energy seperation between these molecular states because a photon can only be absorbed if it has exactly the right energy to excite the molecule to a higher internal energy state. Hence stuctural information can be deduced from the energies of the photons that a molecule absorbs |
| which neigbouing levels are ~ 1000 more closely soaced than vibrational levels? |
Rotational levels
vibrational levels are ~1000 more closely spaced than electronic levels |
in order of closely spacedness name the 3 molecular energy levels.
Hint (RVE) Riding is Very Energetic |
| Rotaional ~ 1000 closely spaced than Vibration that is ~ 1000 more closely spaced than electronic levels |
| a consequence of quantixation is that THERMAL ENERGY in molecular substances is mainly distributed at what? |
Translational and Rotational energy. At all ordinary temperatures (0-500K) virtually all molecules are in their lowest (or ground) vibrational and electronic state
|
different spectroscopic techniques are the study of different types of molecular transition
what do each of these measure?
microwave spectroscopy infra red spectroscopy UV/visible spectroscopy |
microwave spec - rotational transitions infra red spec - vibrational transitons uv/visible spec - electronic transitions |
name the two ways spectra can be recorded.
do they give similar or different information?
which one is much more widely used? |
can be recorded as absorbtion or emission
they give similar information but absorbtion spectroscopy is much more widely used |
