They want to get as far away from each other possible, the ideal angle is 120. But what we have here is a four-membered ring, so what angle does 90° that have to be, that bond? 90 degrees.

它们想要尽量远离彼此，最理想的是形成120°键角,但现在是个四元环,所以这键角应该多大？

麻省理工公开课 - 化学原理课程节选

It means that we better get away from these deterministic models where we have a little electron here with its potential energy and its kinetic energy.

它的意思是我们最好远离,这些确定性模型,那里有一个小电子,它具有势能和动能。

麻省理工公开课 - 固态化学导论课程节选