Atomic Structure

Página 1

Atomic Structure:

A mass spectrometer is used to separate ions having nuclei of differing mass, which can also be used to help identify complex molecules.

Ionisation:

-A sample is placed in the spectrometer and if not already a gas it is vaporised.

-Sample is dissolved and pushed through a small nozzle at a high pressure.

-High voltage applied to make electrons be lost turning the sample into a gas made up of positive ions. (electrospray ionisiation)

-These atoms are diffused into the path of the electrons from the electron gun and eventually ionised.

-The gun fires high energy electrons which knock out an electron from gaseous particles so they form positive ions.

-Doubly charged ions can also be produced but in smaller amounts as more energy is required to knock off two electrons.

Acceleration:

-Ions are accelerated to make sure they all have the same kinetic energy.

-Positive ions are accelerated due to electric field and focused onto a beam (passing through a series of slits).

-Ions with a lower mass to charge ratio experience a greater acceleration.

Deflection:

-The beam of fast moving positive ions is deflected by the magnetic field. The magnitude of the deflection depends on the mass to charge ratio of the ion. When m/z is small the deflection is large.

-The more the ion is charged the more it gets deflected.

Detection:

-Ions in beam detected electrically

-As ion hits detector, it accepts an electron which is amplified and signaled to the computer.

Uses:

-to measure relative atomic masses

-to find the relative abundance of is isotopes in a sample of an element

-check fragments that a molecule might break into so that the identity of the molecule can be found.

Página 2

Electronic Structure:

Electron shells are made up of sub-shells and orbitals. in the current model electrons have fixed energies. They are able to move around in energy levels.