Relative mass - 2.2 - (2)
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What do most elements contain a mixture of?
isotopes, each with a different relative isotopic mass
What is relative atomic mass?
the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12
What does the weighted mean mass take account of?
the percentage abundance of each isotope and the relative isotopic mass of each isotope
In the periodic table, in addition to the atomic number, each element is…
shown with its relative atomic mass
How are percentage abundances of the isotopes in a sample of an element found?
using a mass spectrometer
Are there different types of mass spectrometers?
yes
Do all mass spectrometers work to the same basic principle?
yes
Basic principle of mass spectrometers - 1) A sample is…
placed in the mass spectrometer
Basic principle of mass spectrometers - 2)The sample is vaporised and then…
ionised to form positive ions
Basic principle of mass spectrometers - 3) The ions are accelerated. Heaver ions move more…
slowly and are more difficult to deflect than lighter ions, so the ions of each isotope are separated
Basic principle of mass spectrometers - 4) The ions are detected on a mass…
spectrum as a mass-to-charge ratio m/z.
Basic principle of mass spectrometers - 4.1) Each ion reaching the detector adds to the…
signal so the greater the abundance, the larger the signal
mass-to-charge ratio m/z =
relative mass of ion / relative charge on ion
For an ion with one positive charge, what is this ratio equivalent to?
the relative isotopic mass, which is recorded on the x-axis of the spectrum
What is the percentage abundance?
how much of that isotope we have
What does m/z / mass to charge ratio mean?
tells us the different isotopes that have come through the mass spectra
To calculate relative atomic mass - 1) Multiply them all, add them together and then…
divide them by 100 or total abundance
To calculate relative atomic mass - Add up all abundances for…
total abundance
To calculate relative atomic mass - After you get the answer after dividing by total abundance or 100, look at the…
periodic table to see which element it is