| Valency = 1- | Valency = 2- | Valency = 3- | Valency = 4- | | :--- | :--- | :--- | :--- | | (Monovalent) | (Divalent) | (Trivalent) | Tetravalent | | F^1–^ (Fluoride) | O^2–^ (oxide) | N^3–^ (nitride) | C^4–^ (carbide) | | Cl^1–^ (Chloride | S^2–^ (sulphide) | P^3–^ (phosphide) | | | Br^1–^ (Bromide) | | | | | I^1–^ (Iodide) | | | | | H^1–^ (Hydride) | | | | ** Writing Empirical Formula of Binary Ionic compounds: ** The basic principle for writing the formula (empirical formula) of an ionic compound(neutral) is to make *charge balance*. The total +ve charge of the +ve ions should be equal to the total –ve charge of the –ve ions. The positve ion is written first follwed by the negative ion. **Cross-over Rule: Aluminium oxide:** While writing formula of an