A the concentration gradient!
It slowly gets compressed so I guess you can say it moves slowly as the space gets compressed
<span>We know that electrons are occupied on a cloud surrounding
the nucleus. So which means that the bigger the electron cloud, the bigger the
number of electrons. So in this case, since Na shrank so it lost some
electrons. And since Cl+ grew in size of the electron cloud so electron was
added to it.</span>
