UNIT 1.2 SPECTROSCOPY OF THE ELEMENTS

MASS SPECTROMETER

We've started talking about the periodic table and even used the mass of elements in calculations but how did we get them?  Mass spectroscopy.

So let's say you have a sample that you want to know what it is at an atomic level.   Put it in a mass spectrometer.  Step 1 vaporizes the sample.  Step 2 the gas is then hit with an electron beam to ionize the sample.  Step 3 uses electric fields to accelerate the ions made.  They fly down to step 4 which uses a magnetic field to separate the mass to charge ration.  Think of it this way, if it is heavier it is harder to move.  Step 5 uses a detector to give you a readout of the mass versus the intensity %.  

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So the sample shown in the picture is of 1 element.  But there are 2 amu values.  If you look at a periodic table, we are looking for an element between these 2 numbers (but closer to 35).  This must be chlorine (Cl).  Why does it have 2 and why is the value on the periodic table 35.453? 

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The periodic table value is actually calculated by the relative abundance on Earth.  So all over the world these samples are run and the overall value is agreed upon by scientists and put on the periodic table.