Fichas
Spectroscopy
Fichas del conjunto (23)
- 1SpectroscopySpectroscopy is based on the measurement of absorption or emission of electromagnetic energy by a sample!
- 2This may be by molecules (molecular) or atoms (atomic)Radiation energy includes; visible light,UV radiation, infra red, radio f
requency, xrays - 3Introduction to Spectroscopy techniquesThe most widely used techniques are based on visible light, UV radiation, IR radiation and NMR becoming more widely used.
Each type of technique is distinct in that they monitor different types of molecular and or atomic transitions within the molecule/ atom of the sample - 4Basic PrinciplesElectromagnetic radiation is a form of energy that shows both electrical and magnetic characteristics.
Electromagnetic radiation can be considered to be a stream of separate groups of electromagnetic waves (photons)
The energy that is associated with electromagnetic radiation is related to the waveform. - 5Electrical fieldAt right angles of the electrical field waveform there is the magnetic field which oscillates at the same frequency.
From this we can define wavelength and frequency. - 6Wavelengththe distance between successive peaks
measured in (nm) - 7frequencythe number of successive peaks that pass a given point in 1 second
- 8Energy relationshipsAssociated energy of electromagnetic radiation is directly related to frequency and so is inversely related to wavelength
- 9EquationE = hv = hc/wavelength
- 10PhotonsThe particles of energy moving through space with wavelike properties are called photons.
In the energy relationships, E is the energy of the photons associated with a particular wavelength and so frequency.
Photons are discrete packets of energy - 11Energy in molecules and atomsTo appreciate absorption of energy by atoms and molecules it is necessary to consider energy distribution within atoms and molecules.
Energy content of matter is quantized.
Internal energy of atoms and molecules does not vary in a continuous manner.
They are normally in state of lowest energy. - 12Internal energy of molecules and atomsenergy associated with electrons
energy associated with vibrations
energy associated with rotations
Emol= E(elect)+E(vibr)+ E(rot)
In atoms, no vibrational or rotational energy involved. - 13AlterationInternal energy levels can be altered by absorption or emission of energy as radiation (photons)
Any atoms or molecule can only exist in a limited number of "permitted" energy levels.
Any changes in energy level must but in definite steps. - 14Photo slide here.Only photons of a particular frequency and wavelength will be selectively absorbed or emitted.
The set of available or "permitted" energy levels for any given atom or molecule will be distinct for that species. - 15P2Each element, or compound will have characteristic "permitted" energy levels and so absorb and emit characteristic photons.
So the wavelength and or frequency radiation absorbed or emitted by a species will identify- qualitative spec. - 16Quantitative spectroscopyMeasurement of the amount of radiation involved at the characteristic wavelength or frequency gives information on the number of absorbing or emitting atoms or molecules.
- 17On absorption of photons,the increase in internal energy of a molecule is accommodated in the vibrational, rotational and electric energies.
Absorption of electronic energies cause transition of the electron between orbitals. - 18Flame atomic spectroscopyThe liquid sample is aspirated into a spray chamber where it is formed into a fine spray of droplets - nebulisation
- 19The spray and fuel gases are carried to the flame.The solvent is immediately evaporated and salt particles vaporised.
- 20The molecular associations in the vapour are broken - molecular association to form some free ground state atomssome of the atoms formed in the flame may gain the correct amount of energy to be raised to the next energy state from the flame. some may be ionised by majority will remain in ground state
- 21Remember...Atoms of a particular element absorb only a specific quanta of energy related to promotion of the outer electron to excited states.
- 22specific energyAs such, the energy that atoms of each element can absorb is different to all other elements.
- 23Characteristic energyThe energy is specific to the energy required for transitions of that element.
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- Descripción
- Third level Food Analysis Fichas sobre Spectroscopy, creado por aisling-hefferna el 11/11/2015.
- Creado por
- aisling-hefferna · nov 2015
- Actualizado
- 17 dic 2016
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