15.3 Absorption & Emission

Absorption

If you recall the equation for electric potential energy, ${U_E=k\frac{q_1q_2}{r}}$, you can see that the electrons orbiting the nucleus will have some negative potential energy. As they move to a higher position further from the nucleus, their potential energy will increase. Due to conservation of energy, the electrons must be given some energy in order to jump that gap and get to a higher energy level. This energy comes from photons.