Isotopes
Isotopes are:
The same element
They occupy the same position in the periodic table
They have:
The same number of protons.
A different number of neutrons
A different mass number to their general element (please see atomic and mass numbers)
In 1913 it was discovered that some elements could have atoms with different masses. A device known as a mass spectrometer could compare the relative atomic masses of atoms.
Picture from scienceaid.co.uk
The mass spectrometer is organised into four main sections:
1) Vaporisation
2) Ionisation
3) Acceleration
4) Deflection
5) Detection
1) Vaporisation
2) Ionisation
3) Acceleration
4) Deflection
5) Detection
Vaporisation
Each stage has a different fuction; during vaporisation an element introduced into the chamber is vaporised. All this means is that the element is changing its state to a gas which would allow it to into the next stage of the process which is called ionisation.
Ionisation
During this next stage the atoms are bombarded with electrons. As you should know, all atoms have electrons on their shells. When these atoms are bombarded with a stream of high-energy electrons there is a very good chance that the electrons present on the atom will get knocked out of their current position, sometimes two may be removed. Once the atoms have lost electrons they have therefore lost a negative charge (as all electrons are negative) hence they become a positive ion.
For example Na ------> Na+ (this means the sodium atom has lost one electron and becomes a positive ion)
Acceleration
The next phase is the acceleration of these ions; they are passed through holes in parallel plates to which an electric field is applied. It is this electric field that is responsible for the the acceleration of these ions. The ions make there way to the next stage which is the magnetic field.
Deflection
This is where the ions would now encounter a strong magnetic field. However they are not all defelected the exact same, they deflected according to their mass and charge.
Please be aware that particles can only pass through the instrument if they are positively charged (they have to lose electrons to become a positive ion).
Detection
If the electric and magnetic field stay constant only ions of a particular mass/charge will be detected by the ion detector. Ions with a smaller mass/charge will be deflected too much and ions with a large mass/charge will be deflected to little. If the strength of the magnetic field is increased the detector will then start to detect ions of a greater mass/charge.
See results below of what to expect from a mass spectrometer.
Each stage has a different fuction; during vaporisation an element introduced into the chamber is vaporised. All this means is that the element is changing its state to a gas which would allow it to into the next stage of the process which is called ionisation.
Ionisation
During this next stage the atoms are bombarded with electrons. As you should know, all atoms have electrons on their shells. When these atoms are bombarded with a stream of high-energy electrons there is a very good chance that the electrons present on the atom will get knocked out of their current position, sometimes two may be removed. Once the atoms have lost electrons they have therefore lost a negative charge (as all electrons are negative) hence they become a positive ion.
For example Na ------> Na+ (this means the sodium atom has lost one electron and becomes a positive ion)
Acceleration
The next phase is the acceleration of these ions; they are passed through holes in parallel plates to which an electric field is applied. It is this electric field that is responsible for the the acceleration of these ions. The ions make there way to the next stage which is the magnetic field.
Deflection
This is where the ions would now encounter a strong magnetic field. However they are not all defelected the exact same, they deflected according to their mass and charge.
Please be aware that particles can only pass through the instrument if they are positively charged (they have to lose electrons to become a positive ion).
Detection
If the electric and magnetic field stay constant only ions of a particular mass/charge will be detected by the ion detector. Ions with a smaller mass/charge will be deflected too much and ions with a large mass/charge will be deflected to little. If the strength of the magnetic field is increased the detector will then start to detect ions of a greater mass/charge.
See results below of what to expect from a mass spectrometer.
picture from www.chemguide.co.uk
The results appear as a graph, along the x axis you have the relative atomic mass and on the y axis you have relative abundance which is the measurment of the different amounts of ions present.
