The lowest lying excited state of sodium is 2.104 eV above the ground state. Given that Planck's constant is 4.135x10 (to the negative 15 pwr.) eV/Hz, what color of light do you expect sodium atoms to give off? Table salt is the crystal sodium-chloride NaCl. If you have a gas burner in your kitchen, take some salt and throw it onto the flame. The flame will excite the sodium atoms to this excited state, and they will then fall back down to the ground state giving off a spontaneous emission photon. What color do you see form the salt in the flame? Does it agree with your prediction?