Question

Essentially, I am told electron shell closest to the nucleus is the lowest energy level and subsequent shells have higher energy (I.e. those further from the nucleus). But..... electrons in the furthest shell require the least amount of energy to remove them, so why is this not the lowest energy level? I think I may be conflating different concepts, but want to understand the fundamentals so that I can build on that. Any advice gratefully received.

Answer 1

The contradiction between electron energy levels and the ease of electron removal arises from the difference between the energy of an electron and its ionization energy. Electrons in outer shells are at higher energy levels but require less energy to remove due to effective nuclear charge and electron-electron repulsion.

Step-by-step explanation:

You are correct in noting that the electron shells closest to the nucleus hold electrons with the lowest energy, and that as we move away from the nucleus to higher shells, the energy levels of the electrons increase. This might seem paradoxical since the electrons furthest from the nucleus require the least energy to be removed.

This is because while the energy of an electron indicates how tightly it is bound to the nucleus, the energy required to remove it, known as its ionization energy, is affected by not just its own energy level but also by the effective nuclear charge and the presence of other electrons.

For the electrons in the outermost shell, known as valence electrons, the effective nuclear charge they feel is less due to the shielding effect of the inner electrons. Thus, these valence electrons, while at a higher energy level if isolated, are actually more loosely held in the environment of the atom and require less energy to remove.

Additionally, electrons in full or nearly full shells exhibit greater force of repulsion, making them easier to remove than if they were in a less populated shell closer to the nucleus.