• The chemical formula of a compound indicates its constituting elements and the number of atoms of each combining element.
  • In molecular compounds, the combining capacity, i.e., valency of each combining element determines the chemical formula of the compound.
  • Chemical formula is a short representation of a compound with the help of symbols and valency of elements.
  • The formula of a compound represents atoms of all the elements present in it and number of each type of atoms.
  • CCl4, H2O, HCl, H2S, CH4, CO, CO2, PCl5, PCl5, PCl3, N2O5 are examples of molecular compounds.
  • The formula of ionic compounds show the simple whole number ratio of ions in it, i.e., the positive and negative ions.
  • Chemical equations is short representation of chemical reaction with the help of symbols of elements and formulae of compounds.
  • Reactants are substances taking part in reaction and products are substances formed.
  • Chemical reaction is a process in which one substance changes into another substance.
  • In ionic compounds, charge on each ion is used to determine the chemical formula of the compound.
  • A complete reaction represents symbolically the reactants, products, their physical states and conditions under which a reaction occurs.
  • The equation is balanced in term of mass number of atoms and charges in ionic reaction.
  • Combination reaction involves combination of two substances to produce new substance.
  • Decomposition reactions are those in which a compound breaks down into simpler substances.
  • Displacement reaction is reaction in which more reactive element can replace less reactive element.
  • Double displacement reaction involves exchange of ions between two compounds.
  • Precipitation reactions produce insoluble salts.
  • Oxidation is a process which involves loss of electrons.
  • Reduction is a process which involves gain of electrons.
  • Redox reactions are those in which oxidation and reduction, i.e., loss or gain of electrons takes place simultaneously.
  • Oxidising agent is a substance which can gain electrons easily, e.g., non-metals are good oxidising agents.
  • Reducing agents are those substances which can lose electrons easily, e.g., metals are strong reducing agents.
  • Oxidising agent gets reduced whereas reducing agent gets oxidised.
  • Decomposition reaction carried out with the help of electricity is called electrolysis.
  • Photochemical reactions are chemical reactions taking place in presence of sunlight.
  • Ionic reactions are those which involve ions, positive or negative charged ions. The total charge on both sides as well as number of atoms of different elements should be equal in balanced ionic equation. They are fast reactions.
  • Reactions involving the gain or loss of oxygen or hydrogen by substance. Oxidation is gain of O2 or electronegative element, removal of H2 or electropositive element of loss of electrons. Reduction is process in which H2 or electropositive element is added, O2 or electronegative element is removed or gain of electrons takes place.