Ionic formulae

• Compounds are substances formed when atoms of two or more elements join together
• The name of a compound can tell you what elements are joined together in the compound
• If the compound name ends with –ide then there are only 2 elements joined in it
• If the compound name ends with –ate or -ite then there is also oxygen in it
• Examples of compounds:

  • Magnesium oxide: magnesium and oxygen
  • Silver chloride: silver and chlorine
  • Lead sulfide: lead and sulfur
  • Iron oxide: iron and oxygen
  • Copper carbonate: copper, carbon, and oxygen
  • Zinc sulfite: zinc, sulfur, and oxygen
  • Iron sulphide: iron and sulfur
  • Sodium nitrate: sodium, nitrogen, and oxygen
• Chemical Formula tells you the number of atoms in a compound and the ratio they are to each other
• There are 2 ways to determine chemical formulae: by the elements' valency and by using prefixes
• Prefixes in chemical names indicate the number of atoms of each element in a compound

  • mono-: 1
  • di-: 2
  • tri-: 3
  • tetra-: 4
  • penta-: 5
  • hexa-: 6
• Valency is the same as the number of unpaired electrons

  • Valency rules help determine the ratio in which elements combine to form compounds
  • Example valency values:

  Fluorine: 1

  Sulfur: 2

  Helium: 0

  Carbon: 4

  Nitrogen: 3

  Hydrogen: 1

  Aluminium: 3

  Magnesium: 2
• Writing formulae:

  • Write down symbols of elements involved
  • Write valency of each element
  • Swap valency numbers over
  • Divide by a common factor
  • Re-write the formula
• Examples of writing formulae:

  • Phosphorus oxide: PO3
  • Magnesium sulfide: MgS
• Examples to try:

  • Hydrogen sulfide
  • Hydrogen chloride
  • Aluminium oxide
  • Carbon nitride
  • Hydrogen fluoride
  • Carbon chloride
  • Silicon oxide
  • Carbon hydride
  • Nitrogen iodide
  • Boron bromide
• Roman numerals are used for transition metals to indicate varying valencies

  • Example: copper(II) chloride
• Examples of writing formulae using Roman numerals:

  • Iron(II) oxide: FeO
  • Cobalt(II) nitride: Co3N2
  • Nickel(I) chloride: NiCl
  • Silver(I) oxide: Ag2O
  • Iron(III) bromide: FeBr3
  • Chromium(VI) oxide: CrO3
• Group ions contain more than one type of atom and cannot be split

  • Valency of group ions is determined by the charge in front of the ion
  • Example: carbonate ion (CO3)2- has a valency of 2
• Examples of writing formulae using group ions:

  • Magnesium sulfate: MgSO4
  • Ammonium carbonate: (NH4)2CO3
• Examples to try:

  • Aluminium nitrate: Al(NO3)3
  • Calcium sulfate: CaSO4
  • Ammonium hydroxide: NH4OH
  • Copper(II) carbonate: CuCO3
  • Iron(III) sulfite: Fe2(SO3)3
  • Magnesium phosphate: Mg3(PO4)2
• In ionic formulae, charges must be shown

  • Charge on ion is equal to the valency number of the element or group ion
• Examples of writing ionic formulae:

  • Sodium fluoride: Na+F-
  • Potassium sulphide: (K+)2S2-
  • Aluminium oxide: (Al3+)2(O2-)3
  • Ammonium chloride: NH4+Cl-
  • Iron(II) oxide: Fe2+O2-
  • Sodium hydroxide: Na+OH-
  • Zinc(II) nitrate: Zn2+(NO3-)2
  • Ammonium sulphate: (NH4+)2SO42-
  • Copper(I) nitride: (Cu+)3N3-
  • Calcium hydroxide: Ca2+(OH-)2
• Transition metal valencies can vary in different compounds

  • Valency of transition metals is shown as a Roman numeral in brackets after the element's name
• Examples of writing formulae using Roman numerals:

  • Copper(I) oxide: Cu2O
  • Nickel(II) sulfide: Ni2S2
• Examples to try:

  • Iron(II) oxide: FeO
  • Cobalt(II) nitride: Co3N2
  • Nickel(I) chloride: NiCl
  • Silver(I) oxide: Ag2O
  • Iron(III) bromide: FeBr3
  • Chromium(VI) oxide: CrO3
• Balanced chemical equations show the correct formulae of all substances involved in a reaction

  • State symbols indicate the state of the reactant/product (solid, liquid, gas, aqueous)
• Examples of balanced chemical equations:

  • CH4(g) + O2(g) -> H2O(l) + CO2(g)
  • CH4(g) + 2O2(g) -> 2H2O(l) + CO2(g)
• Examples to try:

  • Methane + oxygen -> water + carbon dioxide
  • Kerosine + oxygen -> carbon dioxide + water
• In a chemical reaction, atoms are rearranged into new substances without losing or gaining atoms

  • A balanced equation shows this rearrangement
• Examples to try:

  • Methane + oxygen -> water + carbon dioxide
• Potassium iodide and lead(II) nitrate react to form lead(II) iodide (yellow solid) and potassium nitrate (colorless solution)
• Molten iron is produced when aluminium reacts with solid iron(III) oxide, forming solid aluminium oxide as a product
• Solid calcium carbonate reacts with hydrogen chloride solution to produce calcium chloride solution, water, and a gas that turns limewater from colorless to milky
• Magnesium burns in oxygen to form solid magnesium oxide
• Potassium metal reacts with water to produce hydrogen gas and potassium hydroxide salt
• Calcium metal added to a solution of aluminium chloride forms aluminium metal and calcium chloride solution
• Silver(I) oxide powder breaks down to produce silver and oxygen
• Formula mass is calculated by adding up the relative atomic masses of every atom present in the substance
• Gram Formula Mass (GFM) is the mass of one mole of a substance in grams
• A solution is formed when a solute is dissolved in a solvent
• Concentration of a solution is the number of moles of substance dissolved in 1 liter of water (molarity)
• Standard solution is a solution of accurately known concentration
• A balanced equation provides information about the relative quantities of reactants and products in a reaction