Atomic Structure

Evolving ideas of atomic stucture

• John dalton etc

Mass Spectrometry

• The mass spectrometer determines the mass of separate atoms or molecules, and so can be used to find the average mass of a sample.
• In mass spectrometry using a time of flight (ToF) instrument, the substances in the sample are converted to high speeds (which depend on their mass to charge ratio), and arrive at a detector.
• STEP 1: Sample investigated is dissolved in a volatile liquid and injected through a fine hollow needle into the ionisation area whilst passing over a heater, turning the substance into gas.
• STEP 2: This vapour passes through an electron gun which bombards the atoms with electrons, knocking out electrons and forming positive ions.
• STEP 3: The positive ions are accelerated as they pass through an electromagnetic field (the acceleration area), giving each the same amount of kinetic energy.
• STEP 4: As the ions all have the same kinetic energy, the speed they travel at through the drift region is inversely proportional to their mass, so separating the ions within the focuses beam produced as they pass through a slit.
• STEP 5: When the ions hit the detector a charge is created. The amount of charge is relative to the abundance of the isotope in the sample - all of the atoms of one isotope will arrive at the same time.

Electron Arrangements and Ionisation Energy

Atomic Stucture and Isotopes