A05 Explain why there is a specific interatomic bond distance.
If two atoms (M1 and M2) interact with each other in space, they feel an attraction force. This attractive force (+) increases as the two atoms approaches each other. However, when they approaches each other, they also start to repel each other. The repulsion force (-) is a short range force compared to the attractive force, which means that it is first when the two atoms are close to each others as the repulsive force is noticed. However, when the repulsive force start to counteract the attractive force, it increases faster in strength than the attractive force does. By subtracting the repulsive force value (negative value) from the attractive force value (positive value), it is possible to construct a force balance curve (broken line in the graph below). As seen from the drawing, the force balance curve shows that M2 feels an increase in attraction until it reaches a maximal value, whereupon the attraction decreases as M2 approaches M1. At a certain distance (equilibrium position), the attractive and repulsive forces balance each other. This distance represents the interatomic bond distance (shown as a green horisontal line from M1). If M2 then is moved closer to M1, M2 will be repelled (negative value along the force balance curve).
By use of this curve, we can see that if two atoms are in equilibrium with each others, they are located at the interatomic bond distance. If one tries to separate the two atoms, they pull back because attraction dominates. If on the other hand one tries to force them closer, they repel each other.
Force balance curve
Stronger attraction (stronger bond strength) results in a steeper and higher force balance curve.
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