Final answer:
According to the Bohr model, electrons move around the nucleus in specific orbits called energy levels, with electrons filling orbitals in a consistent order. The electrons in the outermost energy level determine an atom's stability and its ability to form chemical bonds.
Step-by-step explanation:
According to the Bohr model, electrons encircle the nucleus of the atom in specific allowable paths called orbits. These orbits have fixed energy levels, with the closest orbit having the lowest energy. Electrons fill these orbitals in a consistent order: they first fill the orbitals closest to the nucleus, then they continue to fill orbitals of increasing energy further from the nucleus. The electrons in the outermost energy level determine the atom's energetic stability and its tendency to form chemical bonds with other atoms.