How we can add electron to atom if it is too small?

Why do neutral atoms of Chalcogen or Alkali metals emit photons/energy when you add an electron to them?

• I have problems with understanding why neutral atoms of Chalcogen or Alkali metals would emitt photons/energy when you add an electron to them. Can somebody explain in simple details why adding an electron to an neutral atom would emitt energy and were does the energy come from?

• Answer:

  Anytime you release energy, you are releasing electromagnetic waves. If that energy corresponds to visible wavelengths, you see emitted light. Likewise, in reverse. The energy is proportional to the frequency by Planck's constant.