The Bohr model of the atom, proposed by Niels Bohr in 1913, was a significant advancement in our understanding of atomic structure. According to this model, electrons occupy specific energy levels or orbits around the nucleus, and each orbit corresponds to a specific energy level. The key idea behind the Bohr model is that electrons move in stable, quantized orbits without emitting or absorbing energy.
In the Bohr model, the electron's motion in its orbit is governed by the balance between the attractive force of the positively charged nucleus and the centrifugal force due to the electron's motion. These forces are balanced such that the electron remains in a stable orbit.
When an electron is in a particular orbit, it possesses a specific amount of energy. According to Bohr's model, electrons can only occupy certain discrete energy levels. The electron is said to be in a "stationary state" or an "allowed orbit" when it is in one of these energy levels.
Now, according to classical electromagnetic theory, an accelerated charged particle (like an electron) emits electromagnetic radiation. If the electron were to move in a circular orbit, it would undergo acceleration, continuously losing energy and spiraling into the nucleus. This contradicts the stability of atoms observed experimentally.
Bohr resolved this contradiction by proposing that electrons can only exist in certain discrete orbits with specific energies. These orbits are called "stationary states" or "energy levels." The electron is not considered to move within the orbit as a classical particle but rather exists in a probability distribution around the nucleus. It's important to note that the Bohr model is a simplified representation of atomic structure and doesn't fully capture the behavior of electrons as quantum mechanics does.
In quantum mechanics, electrons are described by wavefunctions, which give the probability distribution of finding an electron in a particular region around the nucleus. These wavefunctions describe the electron's behavior as a wave rather than a classical particle with a definite position and trajectory.
In summary, the Bohr model of the atom proposed that electrons occupy specific energy levels or orbits around the nucleus. The model suggests that the electron doesn't move inside its own orbit after completing one revolution, but rather exists in a probability distribution around the nucleus, described by wavefunctions in quantum mechanics.