posted by danny123 .
An atom contains a total of 29 electrons. When the atom is in the ground state how many principle energy levels will contain electrons?
How do you figure this out?
Remember how the orbitals fill.
3s 3p 4s
3d 4p etc.
You can have 2 s electrons, 6p electrons, and 10 d electrons.
So let's add them up.
1s2 2s2 2p6 3s2 3p6 3d10 4s1
which gives you 29 electrons; therefore, 4 is the highest principal quantum number.