Things to remember: unit 2 and 3

• Properties of protons, neutrons and electrons

  • Relative mass
  • Relative charge
  • Location in the atom
• Protons: 1, 1+, nucleus
• Neutrons: 1, 0, nucleus
• Electrons: 1/1836 or negligible, 1-, shells
• The periodic table lists the elements in order of

  The number of protons in the nucleus
• Isotopes


  Atoms of the same element with different numbers of neutrons and different masses
• Isotopes can be represented as

  𝑍𝑋<|>A - the mass number (sum of protons + neutrons)<|>Z - atomic number (number of protons)
• This notation oxygen-16 means
• Different isotopes of the same element react in the same way

  Because they have the same number of outer shell electrons (OR the same electron configuration)
• The standard isotope that all atomic masses are based on is: carbon-12
• Relative isotopic mass


  The mass of an isotope relative to 1/12th of the mass of an atom of carbon-12
• Relative atomic mass


  The weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12
• The weighted mean mass


  An average mass calculated using the percentage abundance of each isotope and the relative isotopic mass of each isotope
• Mass spectrometer


  Used to determine the percentage abundance of each isotope in a sample
• A mass spectrum shows

  The m/z ratio (relative mass of ion to relative charge of ion) on the x axis and the abundance on the y axis
• Working out ionic charges from the periodic table

  • Group 1: 1+ charge
  • Group 2: 2+ charge
  • Aluminium: 3+ charge
  • Group 15: 3- charge
  • Group 16: 2- charge
  • Group 17: 1- charge
• Charges of silver and zinc ions
• How is the ionic charge shown for metals with variable charges

  As a Roman numeral in the name e.g. copper(II) chloride
• Binary compounds


  They contain only 2 elements. The suffix in the second part is -ide
• Polyatomic ions


  Ions with atoms of more than 1 element bonded together. Their suffix is -ate
• List all diatomic molecules

  • H2
  • O2
  • N2
  • I2
  • Cl2
  • F2
  • Br2
• What is 1 mol?

  The amount of a substance that contains 6.02x10^23 particles
• Equation linking mass, moles and molar mass

  1. Amount, n = 𝑚/𝑀

  2. m = n x M

  3. M = 𝑚/𝑛
• Relative molecular mass, Mr


  The mass of a molecule compared to the mass of an atom of carbon-12
• Relative formula mass


  The mass of a formula unit compared to the mass of an atom of carbon-12
• Hydrated salt


  A salt with water being part of their crystalline structure. The water is called water of crystallisation.
• In an experiment, when heating a hydrated salt

  Heat it to constant mass
• This means that the crystals are reheated repeatedly until the mass of the residue no longer changes
• The concentration of a solution is calculated using the equation


  C=𝑛/𝑉 unit moldm-3
• V = volume of the solution, must be in dm-3
• A standard solution


  A solution of a known concentration.
• How to prepare a standard solution

  Dissolve an exact mass of the solute in a solvent and make up the solution to an exact volume.
• What is molar gas volume?


  Vm – the volume per 1 mol of gas molecules at stated temperature and pressure.

  
• At RTP (20℃ & 101kPa) Vm = 24.0 dm3mol-1 = 24,000cm3 mol-1
• Calculating % yield


  Percentage yield = actual yield (in moles)/theoretical yield (in moles) x 100%
• Why is the actual yield lower than the theoretical yield?
• What is the limiting reagent?

  The reactant that is completely used up first and stops the reaction.
• How to find out which is the limiting reagent

  Calculate the moles of the reagents. Use the ratio from the equation.
• If there is a limiting reagent, any further calculations are based on its moles
• Atom economy


  Measures how well atoms have been utilised.