Higher energy of outer orbitals around nucleus I remember reading that the outer orbitals of atom have higher energy. If an electron is given enough energy it goes to higher energy orbitals from $n=1$ to $n=2,3,4...$ 
My question is that why do the outer orbitals have higher energy? Is is because of charges?
 A: I understand you are confused, because the electron's potential (EM) energy is negative. When you say becomes higher, you mean less negative.
Let's say the electron is at a stable energy level around the nucleus as per QM. This is due to certain forces:


*

*the EM force (potential negative energy) keeps the electron close to the nucleus

*the kinetic energy of the electron keeps the electron away from the nucleus

*the HUP keeps the electron away from the nucleus (in case it would get too close)
Now these three forces equal out, and the electron is in a stable QM orbit (not classical orbital).
Now let's say the electron/atom absorbs a photon. The photon's energy gets transferred into the electron, and the electron moves further from the nucleus.
Now let's see the forces away from the nucleus:


*

*the EM force (attraction) between the electron and the nucleus becomes less strong, the potential negative energy decreases, which means higher energy

*the kinetic energy of the electron must decrease, less momentum 

*the HUP becomes less important
So basically the answer to your question is, away from the nucleus, the electron's potential (EM) negative energy decreases, which means higher energy.
A: Although this is quantum mechanical...If I explain in classical way you can think electrostatic force between nucleus and electron is directing inwards and due to this effect electron rotating around nuclear. Then due to rotation there appears a centrifugal force $\frac{m_ev^2}{r}$ directing outward. now when it getting more energy its kinetic energy $\frac{mv^2}{2}$ increased I.e velocity $v$ increased i.e more centrifugal force $r$ also increased .In this way more energy absorbing by electron and due to more outward centrifugal force increases its orbit radius $r$.I know this is classical but I just try to make it simplify.
