Both Rutherford’s and Bohr’s models have electrons orbiting the nucleus. Why did Rutherford’s model fail to explain atomic stability, while Bohr’s model succeeded?
Rutherford’s model proposed that electrons orbit the nucleus. However, a particle moving in a circular path is constantly changing direction, meaning it is accelerating. A negatively charged accelerating electron should continuously lose energy.
As the electron loses energy, it would spiral inward and eventually fall into the positively charged nucleus. If this occurred, atoms would collapse and matter would not exist. Since atoms are stable in reality, Rutherford’s model failed to explain this stability.
To resolve this, Niels Bohr proposed a new model in 1913. He introduced the concept of stationary states as a postulate. He stated that electrons do not move randomly but follow fixed circular paths called stationary states, orbits, or shells.
In a stationary state, the energy of an electron remains constant, even though it is in motion around the nucleus. Because the electron does not lose energy while in these fixed paths, it does not spiral into the nucleus.
Thus, Bohr’s model successfully explained atomic stability. These shells, also called energy levels, are represented by letters K, L, M, N or numbers n = 1, 2, 3, 4.
Explanation
The textbook context highlights that Rutherford's model failed because classical physics dictates that an accelerating charged particle loses energy. Since an electron in a circular orbit is constantly accelerating, it should lose energy, spiral into the nucleus, and cause the atom to collapse. Bohr solved this by postulating 'stationary states', where electrons orbit the nucleus without radiating energy, thus maintaining constant energy and atomic stability.
Solution Steps
Step 1: Explain Rutherford's limitation - an orbiting electron is accelerating and should lose energy, spiral inward, and collapse the atom.
Step 2: Contrast with Bohr's postulate - electrons move in fixed circular paths called stationary states or shells.
Step 3: Conclude with Bohr's success - in a stationary state, the electron's energy remains constant, preventing energy loss and explaining atomic stability.