How strong is a covalent bond?

The rupture force of single covalent bonds under an external Load was measu red with an atomic force microscope (AFM). Single polysaccharide molecules were covalently anchored between a surface and an AFM tip and then stretche d until they became detached. By using different surface chemistries for th e attachment, it was found that the silicon-carbon bond ruptured at 2.0 +/- 0.3 nanonewtons, whereas the sulfur-gold anchor ruptured at 1.4 +/- 0.3 na nonewtons at force-loading rates of 10 nanonewtons per second. Bond rupture probability calculations that were based on density functional theory corr oborate the measured values.