Chapter 17 Spectroscopy Flashcards
what is mass spectrometry
a scientific method used to determine the relative atomic mass of an element or the relative molecular mass of a molecule
describe the first stage of mass spectrometry
the sample is vaporised so that it is in a gaseous state before entering the vacuum
describe the second stage of mass spectrometry
the gaseous sample enters the ionisation chamber where an electron is removed to make the molecule/atom a positive ion
describe the third stage of mass spectrometry
the ions enter the acceleration chamber where their velocities are increased to the same KE
describe the fourth stage of mass spectrometry
the accelerated ions enter the drift region where they separate out due to their varying masses and strike a detector that is tuned to only detect 1+ ions as a mass to charge ration or m/z ration
what does M+ represent
the moecular ion peak
what is the molecular ion peak
the peak furthest to the right of the mass spectra that has a m/z value equal to the Mr/Ar of the whole molecule/atom
why is there sometimes a very small peak one unit to the right of the M+ peak called M+1
1.1% of carbon atoms are carbon-13 increasing the mass of the molecule by 1.
what is the name given to all peaks before the molecular ion peak
fragment ions
what causes fragmentation
when the molecule is vaporised and then ionised it sometimes breaks apart to form two smaller molecules one takes both electrons and one loses both electrons creating a radical and fragment ion
why are fragment ions useful
they allow us to determine the structure of a molecule
what energy can bonds absorb
infrared energy
what can absorbing infrared energy do to a bond
make it vibrate more
what are the two types of bond vibration
bond stretching
bond bending
what two factors affect how much a bond stretches or bends
mass of atoms in the bond
strength of bond
what are the ideal factors for maximum bond vibration
heavy atoms
strong bonds
how does the frequency of infrared vary between bonds
different bonds absorb different frequencies of infrared energy
what does the infrared spectra show
how much infrared of a certain frequency is transmitted through a sample
why are wavenumbers used instead of frequencies
frequencies are extremely large values so using wavenumbers is more convenient
what do the peaks in an infrared spectra mean
infrared energy of that wavenumber has been absorbed by the sample
why is infrared spectroscopy useful
the wavenumbers absorbed correspond to a certain bond so we can determine the different bonds and functional groups present in a molecule
what is the fingerprint region
part of IR spectra below 1500cm^-1 that has multiple peaks so is very complex
why is the fingerprint region useful
because it is so complex every single molecule has its own unique fingerprint region which can be used to identify it
describe the three Ir spectra you need to know and the homologous series they relate to (values not important)
> alcohol - has a broad peak left side for O-H bond
aldehyde/ketone - has a thin peak in the middle for C=O
carboxylic acid - has both thin peak in middle for C=O and broad peak left side for O-H
give two uses of IR spectroscopy
breathalyser
pollutant sensor
how does IR spectra work in breathalysers
they can detect the C-O bond which you shouldn’t be exhaling unless you have an organic compound like alcohol in your system or a rare medical condition. This is indicated by a colour change
how does the IR spectra work in pollutant sensors
they can detect the C=O bonds in carbon dioxide, C-H bonds in methane and O-H bonds in water allowing us to monitor the level of greenhouse gas emissions in an area
what is the first stage of the greenhouse gas effect
UV and visible energy waves emitted by the sun and these high energy waves reach earth
what is the second stage of the greenhouse gas effect
some of the high energy waves absorbed by the ozone layer the rest is re-emitted from the earth into space in all directions as lower energy infrared waves
what is the third stage of the greenhouse gas effect
the IR is absorbed by molecules in the atmosphere increasing bond vibrations and putting the molecules into a higher energy state where they are unstable
what is the fourth stage of the greenhouse gas effect
the unstable molecules want to get rid of their extra and return to a relaxed stable state so emit infrared energy back to earth heating the planet up
give 5 sources of greenhouse gases
general pollution combustion of fossil fuels agriculture deforestation landfills
