http://www.wcnet.org/~chadb/be.html

In the picture above the black dot represents the nucleus and the red dots represent the electrons.  The black circles around the black dot are symbolic of the electron cloud.

In the nucleus there are 4 protons and 5 neutrons.  There are 4 electrons in the electron could with a configuration of 1s²2s².  That means that in the first shell there are 2 electrons and in the second shell there are two electrons.  If Beryllium had a complete second shell there would be 8 electrons.  Since there are only two electrons in the second shell it is easier for the atom Beryllium to loose the two extra electrons as opposed to gaining 6.