Things to note:
  • Word equations consist of chemical names only. Do not include the physical state of substances present, such as aqueous, solid, liquid or gas, in the equation.
  • Chemical equations consist of chemical formula only. Always ensure that you have balanced the equation. Never leave any chemical equation unbalanced.
  • Half-equations are equations involving the transfer of electrons.
  • Ionic compounds consists of positive and negative ions.
  • When drawing the ions, always ensure that the brackets and the charge of the ion is present. The charge should be written as '3+', '3-', etc. The quantity of the charge should come first before the + or - sign.
  • Covalent molecules consist of atoms.
  • When determining the chemical formula of any covalent compounds, use the valency of the elements present to decide. 
  • The valency of the element will also tell us how many electrons it needs to share in order to form a stable electronic configuration.
  • For structural representation or structural formula, a short straight line (horizontal/ vertical/ diagonal, doesn't matter as long as it is straight) will indicate a pair of electrons (2 electrons) shared between 2 elements. 
  • 2 shared electrons will be represented by a straight line, known as single bond.
  • 4 shared electrons will be represented by a double line, known as double bond.
  • Example: structural formula of water, H-O-H. 
  • Metals are made up of positive ion and sea of delocalised electrons.
  • When drawing dot-cross diagrams, different elements should adopt different symbol as its electrons.

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