Write the chemical formulae of the following:
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.

In order to write a chemical formula, the following steps should be followed

Step 1- Write down the symbols of the elements/ions, which combine to form a molecule of the compound, side by side. (While writing the formula of a compound containing a metal and a non-metal, the symbol of the metal is written first followed by that of the non-metal.)

Step 2- Write the valency of each element /ion.

Step 3- Interchange the valencies of the elements /ions and write as the subscript. Write them close together and ignore ‘1’ to obtain the formula.

Step 4- The radical/polyatomic ions must be written in brackets before the subscript is written. In case the number of polyatomic ions is one, the bracket is not required. An example is shown below:

(a) Write the symbol.                                                                     Ca         PO₄

(b) Write the valency of each element                                            2           3

(c) Interchange the valencies of the elements and write as the subscript. Ca₃ ( PO₄)₂                  

(d) Write them close together to obtain the formula.                                  Ca₃(PO₄)₂