Question

An atom contains a total of 29 electrons. When the atom is in the ground state how many principle energy levels will contain electrons?
a: 1
b: 2
c: 3
d: 4

How do you figure this out?

Answer 1

Remember how the orbitals fill.
1s
2s 2p
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.

Answer 2

thanks