last orbital in an atom?

Question

why is the last orbital in an atom usually not full loaded with electrons. example 3s2 3p4 why it is a general behavior of atoms

Answer 1

After the atomic number 3 (it means for shells N, O, P and so on) the filling of the shells show iregularities
the outer shell can only have electrons of subshell s or p which are filled with 2 or 6 electrons so the outer shell have usually a number of electrons between 1 and 8 ( 8= noble gas)
All chemistry is based on this principle called Aufbau

Answer 2

yes. and the aufbau principle states that electrons are added to a lower energy level orbital first .