A06    Demonstrate your understanding of the bonding energy curve as a function of the bond distance.

Assume that two atoms are on infinite distance from each other. As they start approaching each others, they start to attract each others. As the attraction increases, there is a decrease in potential energy between the two atoms. If we decide to set the energy level to zero (could be set to any arbitrary value, but zero is often used for this purpose) when the two atoms are on infinite distance, the energy decreases as the two atoms approaches each other. However, when the two atoms approach each other, a repulsive potential energy level develops that increases as the two atoms come closer and closer. As seen from the energy curve, an energy minimum exists. The location of this energy minimum is the same as the interatomic spacing.

Final potential energy curve

The potential energy curve can also be calculated from the bond force curve. The energy is defined as force x distance. As soon as the bonded atom is moved from its interatomic spacing distance, the force (either repulsive or attractive) increases. However, when one of the atoms is moved away from the other atom, the attractive force starts decreasing at a certain point. However, because the distance increases, the product of force x distance remains rather constant after after the maximal force has been reached. The latter explains why the energy curve levels of to the right in the figure shown above.