How do atomic orbitals differ from Bohr orbits?

Atomic orbitals differ from Bohr orbits as they represent probabilities of finding electrons, unlike Bohr's fixed circular paths.

Bohr's model of the atom, proposed by Niels Bohr in 1913, was a significant step forward in understanding atomic structure. In this model, electrons move in fixed circular orbits around the nucleus, similar to planets orbiting the sun. Each orbit corresponds to a specific energy level, and electrons can 'jump' between these levels by absorbing or emitting energy. This model successfully explained the hydrogen spectrum, but it had limitations. It could not accurately predict the spectra of atoms with more than one electron, nor could it explain the chemical behaviour of atoms.

In contrast, the concept of atomic orbitals emerged from the quantum mechanical model of the atom, which was developed in the 1920s and 1930s. This model views electrons not as particles moving in definite paths, but as 'clouds' of negative charge. An atomic orbital is a region of space around the nucleus where there is a high probability of finding an electron. The shape of an orbital can be spherical, dumbbell-shaped, or more complex, depending on the energy level and sublevel of the electron.

Unlike Bohr orbits, atomic orbitals do not represent fixed paths for electrons. Instead, they provide a statistical description of an electron's location. The electron can be found anywhere within the orbital, but is most likely to be in the regions of highest electron density. This model can explain not only the spectra of multi-electron atoms, but also the shapes of molecules and the formation of chemical bonds.

In summary, while Bohr orbits and atomic orbitals are both concepts used to describe the arrangement of electrons in an atom, they represent fundamentally different views of the electron's behaviour. Bohr's model treats the electron as a particle moving in a definite path, while the quantum mechanical model treats it as a probability cloud. This shift in perspective, from definite orbits to probabilistic orbitals, was a key development in the evolution of our understanding of atomic structure.