Module 2

• Lithium (Li) atom


  Atomic Number: 3, Atomic Symbol: Li, Mass Number: 7
• Atomic Number (Z)


  Number of protons in the nucleus
• Mass Number (A)


  Total number of protons and neutrons in the atom
• Number of neutrons


  A - Z
• Isotopes


  Atoms of the same element with the same number of protons, but different numbers of neutrons
• Isotopes have similar chemical properties because they have the same electronic structure. They may have slightly varying physical properties because they have different masses.
• There are various models for atomic structure
• Relative atomic mass (RAM)


  The weighted mean mass of one atom compared to one twelfth of the mass of one atom of carbon-12
• Relative Isotopic mass


  The mass of one isotope compared to one twelfth of the mass of one atom of carbon-12
• Calculating the Relative Atomic Mass of an Element

  1. (Isotopic mass x % abundance) / 100

  2. (Isotopic mass x relative abundance) / total relative abundance
• Relative molecular mass


  The average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12
• The 160 peak has double the abundance of the other two peaks because there is double the probability of 160 Br79-Br81 + as can be Br79-Br81 and Br81-79
• Summary of most important ions to know

  • Group 1: Hydrogen, Silver, Gold, Ammonium (NH4+)
  • Group 2: Zinc, Copper (II), Iron (II), Tin, Lead
  • Group 3: Iron (III)
  • Group 5: Phosphate (PO4 3-)
  • Group 6: Carbonate (CO3 2-), Sulfate (SO4 2-)
  • Group 7: Nitrate (NO3-), Hydroxide (OH-)
• How to work out the formula from the ionic charge

  1. Identify the ionic charges of the two ions

  2. Combine the ions together to get a neutral compound
• Lithium sulfate


  • Li+
  • SO4 2-
  • Formula: Li2SO4
• Calcium phosphate


  • Ca2+
  • PO4 3-
  • Formula: Ca3(PO4)2
• Writing ionic equations


  1. Take full equation

  2. Separate (aq) solutions into ions

  3. Cancel out spectator ions leaving ionic equation