The energy levels of an electron in an atom are roughly analogous to the steps of a ladder. An electron jumping to higher energy levels can be compared to a workman climbing up a ladder. We are going to compare the energy levels of an electron in a hydrogen atom to a vertical ladder braced upon a wall.

To get to a higher energy level, an electron must gain energy. It does this by absorbing a photon having exactly the right amount of energy for the jump. To climb to a higher step, the workman must use energy. He got this energy from food.

There are some important differences, however. First of all, the energy levels available to an electron are not equally spaced like the steps on a ladder. They get closer together the farther away from the ground state the electron is. If this were a ladder, it would be like stepping smaller and smaller distances as one moved up. The top steps would be barely millimeters apart.