Isotopes, Ions, and Mass Spectrometry Quiz

Isotopes

• Hydrogen, Deuterium, and Tritium are isotopes with 1 proton and 0, 1, and 2 neutrons respectively

Ions and Ionisation

• Ions are formed when an atom loses or gains electrons, resulting in an overall charge
• Ionisation is the process of removing electrons from atoms, resulting in positively charged ions

Mass Spectrometry

• A technique used to identify different isotopes and find the overall relative atomic mass of an element
• Time of Flight (TOF) Mass Spectrometry records the time it takes for ions of each isotope to reach a detector

TOF Mass Spectrometry Process

• Ionisation: a sample is vapourised and injected into the mass spectrometer, where a high voltage is passed, removing electrons and leaving +1 charged ions
• Acceleration: positively charged ions are accelerated towards a negatively charged detection plate
• Ion Drift: ions are deflected by a magnetic field into a curved path, dependent on the charge and mass of the ion
• Detection: positive ions hit the negatively charged detection plate, gaining an electron and producing a flow of charge

Atomic Orbitals

• Orbitals are clouds of negative charge that hold electrons
• There are different types of orbitals: s, p, d, and f
• Each orbital can hold a different number of electrons before the next one is filled: s-orbital = 2 electrons, p-orbital = 6 electrons, d-orbital = 10 electrons
• Energy of orbitals increases from s to d, meaning they are filled in this order

Electron Configuration

• Electrons pair up with opposite spin within an orbital to make the atom as stable as possible
• Electrons in the same orbital must have opposite spin
• Spin is represented by arrows
• Three rules for writing electron configurations:
  • Lowest energy orbital is filled first
  • Electrons with the same spin fill up an orbital first before pairing begins
  • No single orbital holds more than 2 electrons

Analysis and Spectra

• The current values are used in combination with flight times to produce a spectra print-out with the relative abundance of each isotope displayed
• A 2+ charged ion may be produced during ionisation, affecting the magnetic field and resulting in a smaller radius curved path
• The mass to charge ratio (m/z) of a 2+ charged ion is halved and appears as a trace at half the expected m/z value on the spectra

Chlorine Spectra

• Chlorine spectra display a characteristic pattern in a 3:1 ratio for Cl+ ions and a 3:6:9 ratio for Cl2+ ions
• This is due to the relative abundance of isotopes and the formation of chlorine molecules in different combinations