Shells with fixed energy
Bohr's model: stationary states.
Saving the atom
Rutherford's electrons should lose energy and fall into the nucleus. In 1913 Niels Bohr offered a new model.
What did Bohr say about the paths of electrons?
What this lesson covers
The idea
Electrons revolve only in allowed circular orbits called stationary states, shells or energy levels (K, L, M, N… or n = 1, 2, 3, 4…), each of definite energy, and lose no energy there, so the atom is stable.
Saving the atom
Rutherford's electrons should lose energy and fall into the nucleus. In 1913 Niels Bohr offered a new model.
What did Bohr say about the paths of electrons?
- Electrons move only in certain fixed paths and do not lose energy there
- Electrons move randomly around the nucleus
- Electrons sit inside the nucleus
Bohr's shells
Press Next step to build Bohr's picture.
Why the atom does not collapse
In a stationary state the electron's energy stays constant even though it keeps moving. That is how Bohr explained why atoms are stable.
In Bohr's model, electrons revolve only in allowed circular orbits called stationary states, shells or energy levels (K, L, M, N… or n = 1, 2, 3, 4…). Each has a definite energy and the electron loses no energy there, so the atom is stable.
Notes
Bohr's model: electrons revolve only in fixed shells (stationary states, energy levels: K, L, M, N… or n = 1, 2, 3, 4…), each with a definite energy, losing none there, so the atom is stable.
Check yourself
Stationary states are also called …
From the nucleus outward, the shells are named …
How does Bohr's model explain why the atom is stable?
Which shell has n = 3?
- nuclei. The nucleus is the dense centre of the atom, not a path for electrons.
- shells or energy levels — correct. Yes!
- cathode rays. Cathode rays are streams of electrons in a tube.
- A, B, C, D. The names start from K, a naming that came from early X-ray experiments.
- N, M, L, K. The K shell is the one closest to the nucleus.
- K, L, M, N — correct. Yes!
- An electron in a stationary state keeps a constant energy, so it does not spiral inward — correct. Yes!
- The electrons stop moving. Electrons keep revolving around the nucleus.
- The electrons can move anywhere they like. Electrons can revolve only in the allowed shells.
- K. K is the shell with n = 1.
- M — correct. Yes!
- L. L is the shell with n = 2.