To put numbers on this, a typical approximation for bond energy as a function of stretch would be E = 500x^2, where x is the stretch in Angstroms and E is the energy change in units of thermal noise at room temperature (about 0.6 kcal/mol). A bond length deviation of 0.01 Angstroms is already negligible, because its associated stretch energy is far below thermal fluctuation levels. Parts per billion are totally invisible.