Chemistry ions

• What is expected of A Level Chemistry students regarding common ions?

  Students are expected to know the names and symbols of common ions and work out the formulae of ionic compounds.
• What are the symbols of some common positive ions (cations)?

  • Hydrogen: H+
  • Sodium: Na+
  • Silver: Ag+
  • Potassium: K+
  • Lithium: Li+
  • Barium: Ba2+
  • Calcium: Ca2+
  • Copper(II): Cu2+
  • Magnesium: Mg2+
  • Zinc: Zn2+
  • Lead: Pb2+
  • Iron(II): Fe2+
  • Iron(III): Fe3+
  • Aluminium: Al3+
• What are the symbols of some common negative ions (anions)?

  • Chloride: Cl–
  • Bromide: Br–
  • Fluoride: F–
  • Iodide: I–
  • Hydrogencarbonate: HCO3–
  • Hydroxide: OH–
  • Nitrate: NO3–
  • Oxide: O2–
  • Sulphide: S2–
  • Sulphate: SO4^2–
  • Carbonate: CO3^2–
• Why must the number of positive charges equal the number of negative charges in ionic compounds?

  To ensure that the compound has no overall charge.
• What is the formula for sodium chloride?

  NaCl
• How is the formula for magnesium oxide written?

  MgO
• What is the "cross-over" method for determining the formula of ionic compounds?

  1. Write the ions side by side.
  2. Draw arrows that cross each other.
  3. Write the charges at the arrow ends.
  4. Write the formula:

  • Positive ion without charge.
  • Subscript for the number unless it is 1.
  • Negative ion without charge.
  • Subscript for the number unless it is 1.
• What is the formula for magnesium chloride using the cross-over method?

  MgCl2
• How should compound ions be treated when writing formulas for ionic compounds?

  Put brackets around their symbol if more than one is needed to balance the charges.
• What is the formula for magnesium hydroxide?

  Mg(OH)2
• What is the formula for ammonium sulphate?


  (NH4)2SO4
• What is the formula for copper(II) sulphate?

  CuSO4
• What is the formula for sodium hydroxide?

  NaOH
• What is the formula for ammonium chloride?

  NH4Cl
• What is the formula for magnesium chloride?

  MgCl2
• What is the formula for magnesium oxide?

  MgO
• What is the formula for lithium fluoride?

  LiF
• What is the formula for barium sulphate?

  BaSO4
• What is the formula for calcium carbonate?

  CaCO3
• What is the formula for zinc oxide?

  ZnO
• What is the formula for iron(III) oxide?

  Fe2O3
• What is the formula for iron(II) chloride?

  FeCl2
• What is the formula for lead(II) nitrate?

  Pb(NO3)2
• What is the formula for ammonium nitrate?


  NH4NO3
• What is the formula for potassium bromide?

  KBr
• What is the formula for sodium bicarbonate?

  NaHCO3
• What is the formula for calcium hydroxide?

  Ca(OH)2
• What is the formula for magnesium carbonate?

  MgCO3
• What is the formula for ammonium carbonate?

  (NH4)2CO3
• What is the formula for sodium phosphate?

  Na3PO4
• What is the formula for potassium sulfate?

  K2SO4
• What is the formula for ammonium phosphate?


  (NH4)3PO4
• What is the formula for calcium phosphate?

  Ca3(PO4)2
• What is the formula for barium carbonate?

  BaCO3
• What is the formula for strontium sulfate?

  SrSO4
• What is the formula for lithium sulfate?

  Li2SO4
• What is the formula for sodium sulfate?

  Na2SO4
• What is the formula for potassium phosphate?

  K3PO4
• What is the formula for ammonium sulfide?

  (NH4)2S
• What is the formula for calcium sulfide?

  CaS