C1 atomic structure

• the sub-atomic particles are protons and neutrons in the nucleus, and electrons orbiting in energy shells
• relative masses of sub-atomic particles:

  electron = 1/1840

  proton = 1

  neutron = 1
• relative charges of sub-atomic particles:

  electron = -1

  proton = +1

  neutron = 0
• atomic number is the number of protons in the nucleus of an atom
• atomic number is represented by Z
• mass number is the number of protons and neutrons in the nucleus of an atom
• mass number is represented by A
• isotopes are two atoms with the same number of protons and electrons but a different number of neutrons
• isotopes react in the exact same way chemically
• electrons orbit the nucleus of an atom and are held in electron shells which increase in energy the further you get from the nucleus
• electrons can behave as a particle, wave or cloud of charge
• the first shell holds up to 2 electrons, the second shell holds up to 8 electrons and the third shell holds up to 18 electrons
• a mass spectrometer is an instrument which can be used to determine the relative atomic mass of a sample
• there are many types of mass spectrometry but all are based on forming ions and separating the ions based on their charge:mass ratio
• time-of-flight spectrometry records the time taken for ions to reach a detector and uses this to identify them
• TOF spectrometry has the following stages:

  • ionisation
  • acceleration
  • ion drift
  • detection
  • analysis
• in the first stage of TOF spectrometry, ionisation, the sample is vaporised and injected into the chamber
• the two types of ionisation in TOF spectrometry are electron bombardment, where ions lose an electron, and electrospray, where ions gain a proton, both create 1+ ions
• in the second stage of TOF spectrometry, acceleration, the molecules are given energy so they all have the same kinetic energy, then accelerated towards a negative plate
• in the third stage of TOF spectrometry, ion drift, ions are deflected by a magnetic field so travel in a curved path, depending on their charge and mass
• in the fourth stage of TOF spectrometry, detection, positive ions hit negative plate, they gain an electron, this causes a current to flow, greater abundance = greater current
• in the fifth stage of TOF spectrometry, analysis, current values are used in combination with flight times to produce a mass spectrum
• mass spectra are produced from a mass spectrometer, they show the abundance of different ions separated by their mass/charge ratio
• energy levels are divided into sub-levels, named s, p, d and f
• different orbitals have different energies depending on the energy level they are in
• the atomic orbitals of each main level have different shapes with different energies, these are the sub-levels, they represent a volume of space where there is a 95% chance of finding an electron
• s-orbitals can hold up to 2 electrons
• p-orbitals can hold up to 2 electrons each, but come in groups of 3 so 6 electrons in the sub-level
• d-orbitals can hold up to 2 electrons each, but come in groups of 5 so 10 electrons in the sub-level
• electron configuration is written in the form 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 and so on
• the 4s orbital is filled before the 3d orbital because it is of lower energy
• the electron configuration of chromium is 1s2 2s2 2p6 3s2 3p6 4s1 3d5
• ionisation energy is the minimum energy required to remove one mole of electrons from one mole of atoms in a gaseous state
• first IE is shown by the equation:

  $M_{(g)} → M^+$$_{(g)} +$$e^-$
• second IE is shown by the equation:

  $M^+$$_{(g)} → M^{2+}_{(g)} +$$e^-$
• third IE is shown by the equation:

  $M^{2+}_{(g)} → M^{3+}_{(g)} +$$e^-$
• along a period, first IE increases due to decreasing atomic radius and increasing electrostatic forces of attraction
• down a group, first IE decreases due to increasing shielding and increasing atomic radius
• electrospray ionisation of X process:

  • X is dissolved in a solvent
  • X is injected through a needle at high voltage
  • it gains a proton
  • the equation is X + H+ -> XH+
• remember which type of ionisation is which because electrospray ionisation has a p in it so a proton is gained, and electron bombardment has an e in it so an electron is lost

  electron bombardment is the same as electron impact