Spectroscopy
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How does a mass spectrometer work
-determines mass of molecules by measuring the mass - to - charge ratio of ions -the size of the trace produced is dependent in the relative abundance of the ion
How is the mass of the molecular ion the same as that of the compound
Mass of electron is negligible
What is the definition for the molecular ion
The positive ion formed in mass spectrometry when a molecule loses an electron
Which is the molecular ion peak
The clear peak with the highest m/z value on the right hand side of the mass spectrum
What is responsible for the M+1 peak
-The very small peak one unit after the m+ peak is known as the m+1 peak and it exists as some of the carbon present is the carbon -13 isotope (1.1%)
What is fragmentation
The process in mass spectrometry that causes a positive ion to split into peices , one of which is the positive fragment ion
What’s the equation for fragmentation occurring
M+ —-> A+ + B. Molecular ion —> fragment ion and radical
Does the radical produce a peak
No because only the positive ions are detected
How do bonds vibrate
The covalent bonds that join atoms in molecules can absorb infrared radiation. This absorbed energy makes the bonds vibrate
What are the two ways bonds can vibrate
Bending or stretching motion about a central point
What happens to the vibrations with temperature
They increase with temperature
How does the amount a bond stretch or bend depend on the mass of the atoms and the bond strength
-lighter atoms vibrate faster -weaker bonds vibrate slower
How do different covalent bonds have different strengths
This is due to the different masses of the different atoms at either end of the bond. This affects bond strength and length
What happens as a result of differing bond strengths
The bonds vibrate at their own unique frequency. This is measured as wavenumbers in cm-1
What’s the most common frequency
200-4000 this is in the infrared region
What is the impact of this on the environment
The suns visible light and ir radiation passes through the atmosphere and reaches the earths surface where it is absorbed. Some of the ir radiation is remitted by the earths surface as longer wavelength ir
What are 3 greenhouse gases
Water vapour , methane and carbon dioxide
What then happens to the longer wavelength ir
These gases absorb it as it has the same natural frequency as their bonds
Then what happens
Eventually the vibrating bonds in these greenhouse gases re emit this energy as radiation- increasing the atmospheric temperature, leading to global warming.
What are the dips on the infrared spectrum called
Peaks
What can we gather from the peaks
Each peak is at a wavenumber that can be related to a particular bond in the molecule
What does a larger peak tell us
The greater the absorbance
What are some uses of ir spectroscopy
Identification of particular bonds in a molecule and identification of compounds by direct comparison of spectra
What are real world uses of ir spectroscopy
Breathalyser- checking alcohol content in breath Drug analysis in forensic science Checking co2 concentrations in the atmosphere and greenhouses