Bond Making – IGCSE Chemistry Definition

Bond making is the process of forming a new chemical bond between two atoms. It is always an exothermic process, meaning energy is released to the surroundings. When atoms join together, they move to a state of lower energy, and the difference is released as heat. The amount of energy released when a particular bond forms is equal to the bond energy of that bond.

Why bond making releases energy

Atoms bond together because the bonded arrangement is more stable (lower in energy) than the separated atoms. As atoms approach each other and the bond forms, the system moves to a lower energy state, and the excess energy is transferred to the surroundings. Stronger bonds release more energy when they form.

Role in chemical reactions

In any chemical reaction, old bonds in the reactants are broken (endothermic step) and new bonds in the products are formed (exothermic step). The overall energy change depends on the balance between these two steps. If the energy released by bond making exceeds the energy absorbed by bond breaking, the reaction is exothermic. If bond breaking requires more energy than bond making releases, the reaction is endothermic.

In bond energy calculations

After listing the bonds broken and their total energy, candidates list all the new bonds formed in the products and add up their bond energies. This gives the total energy released.

Energy change = total energy to break bonds - total energy released by making bonds.

A negative result means the reaction is exothermic (more energy released than absorbed).

Exam context

Paper 4 examiners often ask candidates to explain why a reaction is exothermic or endothermic in terms of bond breaking and bond making. The key phrase for full marks is: “the energy released by making new bonds is greater than the energy needed to break the bonds in the reactants.”

Worked exam question

In the combustion of hydrogen, 2H₂ + O₂ → 2H₂O, use bond energies to explain why this reaction is exothermic. (H-H = 436, O=O = 496, O-H = 463 kJ/mol) (3 marks)

Bonds broken: 2 x H-H + 1 x O=O = 872 + 496 = 1368 kJ [1]. Bonds made: 4 x O-H = 4 x 463 = 1852 kJ [1]. Energy released by making bonds (1852 kJ) is greater than energy needed to break bonds (1368 kJ), so the reaction is exothermic [1].

Common mistakes

The most frequent error is saying “making bonds requires energy” or “breaking bonds releases energy.” These are backwards. Always remember: breaking requires energy (endothermic), making releases energy (exothermic). A helpful mnemonic at IGCSE is that demolishing a building costs money (energy in), while building one produces something useful (energy out as stability).