I am in the very center of the nucleus of an atom that has only one proton and electron – hydrogen. Now I will tell you where in such an atom there is an electron. I open and close my eyes as fast as I can, each time I see an electron in a different place, sometimes I see it very far away or very close, it happens very rarely, most often I observe it at a certain distance, on average it is equal to 3/2 * 0.0529 nm. Basically, I do not know where I will find an electron when I open my eyes again, but I can tell you what is the probability of seeing an electron at a given distance. The probability of seeing an electron at a given distance slowly increases with increasing distance from the nucleus, is greatest at a distance of 0.0529 nm from its center, and then decreases very quickly.