golemsena

I got this,..

In molecules such as alkanes the most stable comformation is the one where hydrogen atoms are as far apart from each other as possible. But why do they repel each other? I get that electron clouds repel each other, but what about other (attractive) forces such as london dispersion? Also, is the thing only applicable to hydrogens, or in a more general way, every atom tries to be as far away as possible from every other atom? If yes, why and what's the magnitude of these forces? Feel free to answer in depth in you want.