Final answer:
Atoms respond to unfilled energy levels by losing or gaining electrons to form more stable ions, following the quantized nature of electron energy levels and specific orbital filling order.
Step-by-step explanation:
When atomic energy levels are not filled, atoms tend to either lose or gain electrons to achieve a more stable state. This process is driven by an atom's need to fill its outermost energy level with the maximum number of electrons, thereby lowering its potential energy. In this context, atoms of metals such as lithium may lose an electron, resulting in a more stable ion, while nonmetals like fluorine may gain an electron to complete its outer shell.
The filling of atomic orbitals follows a specific pattern: electrons fill orbitals from the lowest energy level up, beginning closest to the nucleus. When multiple orbitals of equal energy exist, they first fill with one electron per orbital before pairing up. This systematic filling reflects the quantum nature of electrons, with energy levels being quantized and electrons requiring specific amounts of energy to move between levels.
As for the structure of the electron configuration, it can sometimes be counterintuitive; for example, after the 3p sublevel is filled, the 4s sublevel fills before the 3d sublevel, despite what might be expected. This phenomenon is a result of the unique energies associated with these orbitals, which have been confirmed by experimental observations and theoretical calculations.