definitions

• Acceleration


  Second stage of TOF spectrometry. The positively charged ions are accelerated by an electric field so that they have the same kinetic energy.
• Atom


  The smallest part of an element that can exist. All substances are made up of atoms.
• Atomic nucleus


  Positively charged object composed of protons and neutrons at the centre of every atom with one or more electrons orbiting it.
• Atomic number


  The number of protons in the nucleus.
• Electron


  Negatively charged subatomic particle which orbit the nucleus at various energy levels. Relative mass of 1/2000.
• Electron configuration


  The distribution of electrons of an atom in orbitals.
• Electron impact ionisation


  Method of ionisation in TOF spectrometry. The sample is vaporised and an electron gun fires high energy electrons at it, causing an electron to be knocked off each particle to produce 1+ ions.
• Electrospray ionisation


  Method of ionisation in TOF spectrometry. The sample is dissolved and pushed through a fine nozzle at a high pressure. A high voltage is applied to it causing each particle to gain an H+ ion. The sample is then turned into a gas.
• First ionisation energy


  The energy required to remove 1 mole of electrons from 1 moles of gaseous atoms to form 1 mole of gaseous 1+ ions. E.g. O(g)→ O+ (g) +e-.
• Ion detection


  Fourth stage of TOF spectrometry. The negatively charged plate detects charged particles and a mass spectrum is produced.
• Ion drift


  Third stage of TOF spectrometry. The ions enter a region with no electric field, so they drift through it. The lighter the ion, the faster they will drift.
• Ionisation


  First stage of TOF spectrometry. The sample can be ionised by electrospray ionisation or electron impact ionisation.
• Isotope


  Atoms of the same element with the same number of protons but a different number of neutrons. E.g. ^35Cl and ^37Cl.
• Mass number


  The total number of protons and neutrons in the nucleus.
• Mass spectrometer


  A mass spectrometer gives accurate information about relative isotopic mass and also about the relative abundance of isotopes.
• Mass spectrometry


  Mass spectrometry can be used to identify elements and determine relative molecular mass.
• Neutron


  Neutral subatomic particle present in the nucleus of the atom. Relative mass of 1.
• Nuclear charge


  Total charge of all the protons in the nucleus. It has the same value as the atomic number. Increases as you go across the periodic table.
• Proton


  Positively charged subatomic particle present in the nucleus of the atom. Relative mass of 1.
• Second ionisation energy


  The energy required to remove 1 mole of electrons from 1 moles of gaseous 1+ ions to form 1 moles of gaseous 2+ ions. E.g. O-(g) → O^2+(g) + e-.
• Sub-shells (orbitals)


  Electron shells are divided up into sub-shells which have slightly different energy levels. The sub-shells have different numbers of orbitals which can each hold up to two electrons. Types of sub-shell: s, p, d and f.
• Time of Flight (TOF) spectrometer

  A method of mass spectrometry where an ions mass-to-charge ratio is determined by a time of flight measurement. Consists of four stages: ionisation, acceleration, ion drift and detection.
• Atom economy


  The measure of the amount of starting materials that end up as useful products.
• Avogadro's constant


  The number of atoms, molecules or ions in one mole of a given substance. 6.02x10^23
• Concentration


  The amount of substance per unit volume. Units given in g/dm^3 or mol/dm^3.
• Empirical formula


  The smallest whole number ratio of atoms of each element in a compound.
• Limiting reactant


  The reactant that is completely used up since it limits the amount of products formed.
• Mole


  The mass of a substance containing the same number of units as there are atoms in exactly 12 g of carbon-12.
• Molecular formula


  The actual ratio of atoms of each element present in a compound.
• Percentage by mass


  A value representing the concentration of an element in a compound or a component in a mixture.
• Percentage yield


  The percentage ratio of the actual yield of product from a reaction compared with the theoretical yield.
• Relative atomic mass


  The average mass of an atom of an element over 1/12th the mass of an atom of carbon-12.
• Relative molecular mass


  The average mass of one molecule of an element or compound compared to 1/12th the mass of an atom of carbon-12.
• Co-ordinate bond


  A co-ordinate (dative covalent) bond contains a shared pair of electrons with both electrons supplied by one atom.
• Covalent bond


  A shared pair of electrons between two non-metals.
• Dipole


  Difference in charge between the two atoms of a covalent bond caused by a shift in electron density in the bond due to the electronegativity difference between elements participating in bonding.
• Electron pair repulsion


  Repulsion that exists between electron pairs due to the negatively charged electrons. This repulsion means electron pairs position themselves as far apart from each other as possible around the central metal atom.
• Electronegativity


  The power of an atom to attract the electron density in a covalent bond towards itself.
• Electrostatic forces


  The strong forces of attraction between oppositely charged ions.
• Hydrogen bonding


  An interaction between a hydrogen atom and an electronegative atom, commonly nitrogen, fluorine or oxygen. The slightly positive hydrogen is attracted to the lone pair on the electronegative atom. Hydrogen bonds are stronger than van der Waals and dipole-dipole forces but weaker than ionic and covalent bonds.