Electromagnetic spectrum Flashcards
what speed does electromagnetic spectrum travels?
3 *10 ^8
the wavelength of each wave length
10^3
10^-2
10^-5
0.5 * 10^ -6
10^-8
10^ -10
10^ -12
Radio waves:
When placed inside a magnetic field, the nuclei of some atoms can spin in two (or more) directions, let’s say ‘up’ and ‘down’. The energy difference between these two states is similar to that of a radio-wave photon,
NMR and MRI imaging.
so radio waves can make nuclei flip spin from up to down, or vice versa.
Microwaves:
The energy of microwaves is enough to make molecules rotate.
rotational spectroscopy, and of microwave ovens
(the spinning water molecules bash into neighbouring molecules and heat them up).
Infrared:.
The energy of IR is now enough to make molecules vibrate. This is the basis of vibrational spectroscopy
Visible light:
In large conjugated molecules (e.g. carotene, chlorophyll, heme, and azodyes) the electronic energy levels are close together. Visible light has enough energy to excite electrons, making these molecules colourful.
Ultraviolet:
The energy of UV is now so great it can excite electrons even in small molecules where the separation between electronic levels is large. This is the basis for UV-vis spectroscopy. In the deep UV it can even break chemical bonds and initiate chemical reactions. In biological systems, this can damage the organism (e.g. sunburn).
X-rays:
The energy of X-rays is now so large that it can eject core electrons from atoms. This is the basis for surface analysis methods like XPS.
EM definitation
a stream of mass-less particles, called photons, each traveling in a wave-like pattern at the speed of light
characteristics of EM
Radio more like waves
gamma more like particle
what is a photon
A photon is an elementary particle that is a quantum of the electromagnetic field
c
3 x 10 8
h plank
6.63 x 10 -34
v
frequency
c
v fancy V
energy
h v
energy
hc/ wavelength
nano
x 10 9
radio
2+ nuclei flip
microwave
molecule rotation
IR
Bond vibrates
UV
valence electron excited. large + small molecules. photon release when back to normal
light
valence electron excite photon light emitted. large molecules
x rays
eject core electrons
ground state
electrons lowest energy level
quanta
it is discrete bundles energy levels in proportional to the frequency of the radiation
energy
it cannot exist between two levels
how to raise energy levels in electrons
put in a photon
what happens
it will move up a energy level
emisson spectra
if you place a wavelength in a gas, some of the wavelengths will be absorbed (photon). this will produce emissions in the spectra and black lines. specific elements have individual spectra
energy levels
is is always negative once it is positive you will say it is ionised
other spectra
electron absorb photon
release photon
specific colour in line
CO2
absorbs in the IR and warms the atmosphere – the Greenhouse effect.
Ozone
absorbs UV light but not visible light – the ozone layer allows visible sunlight through to the planet surface, but protects it from damaging UV.
NMR, UV/vis and IR spectroscopy all
depend on energy quantisation and exploit different types of molecular energy levels (nuclear, electronic and vibrational).
Etotal =
Etrans + Erot + Evib + Eelec
Thus, molecules
have translational, rotational, vibrational and electronic energy levels
,molecule energy
each of which are independent of the others.
Molecules can only exist in certain discrete energy states. They can:
Translate
Rotate
Vibrate
and their electrons can change energy.
Translational energy levels:
if a molecule is in a container of macroscopic size (e.g. this room) translational energy levels are so close together they seem continuous.
Rotational energy levels:
separated by ~10-23 J (~0.006 kJ mol-1)
Rotational energy levels:
separated by ~10-23 J (~0.006 kJ mol-1) value 1
Vibrational energy levels:
separated by ~10-20 J (~6 kJ mol-1)
1000
Electronic energy levels:
separated by ~10-18 J (~600 kJ mol-1)
100,000
that atoms do not have bonds,
so they cannot rotate or vibrate
Each electronic level has
a set of its own vibrational levels…
…and each vibrational level has
a set of its own rotational levels.
continuous spectra (the sun)
continuous means that there are no gasps in wavelength
how to produce continuous spectra
hot/ dense gas — slit — prism detection
emission detection
hot gas of an element
electrons are excited and absorb the heat/ current
it goes through a slit
pass prism
detects wavelength that have been aborbed
Absorption Spectrum:
hot gas
pass through cold gas - it will absorb photon + energy
it will appear as dark lines
why is the sun not continuous spectra
because the cooler atmosphetre
how do we know the sun elements
In 1814, Joseph Fraunhofer studied the dark absorption lines in the spectrum from the Sun. The wavelengths of these lines were identical to those from emission spectra measured on Earth from elements such as sodium, hydrogen, etc. This allowed scientists to work out the composition of the Sun’s atmosphere 93 million miles away!
But there were some lines in the spectrum that had never been seen before on Earth
emission
it loses photon
absorption
it gains photon
modern spectra
sample —– light ——- diffraction grating ——– iris——– detector
