When a 'chemical reaction' takes place, the atoms of the reactants or the products reacting bond with each other.
Explanation: In a chemical reaction, no outside atoms are used and no atoms are created or destroyed. In fact, the 'bonds' between the atoms are broken and then re-arranged in the chemical reaction to make the 'products' of the reaction. These products are not new products but simply products that have been obtained by the re-arrangement of atomic bonds.