A model suggested in 1913 to explain the stability of atoms which
classical electrodynamics was unable to account for. According to the classical view
of the atom, the energy of an electron moving around a nucleus must continually diminish
until the electron falls onto the nucleus. The Bohr model solves this paradox with
the aid of three postulates (→ Bohr’s first postulate,
→ Bohr’s second postulate,
→ Bohr’s third postulate). On the whole, an atom
has stable orbits such that an electron moving in them does not radiate
electromagnetic waves. An electron radiates only when
making a transition from an orbit of higher energy to one
with lower energy. The frequency of this radiation is related to
the difference between the energies of the electron in these two orbits,
as expressed by the equation hν = ε1 - ε2,
where h is → Planck’s constant and ν the radiation
frequency. The electron needs to gain energy to jump to a higher orbit. It gets
that extra energy by absorbing a quantum of light
(→ photon), which excites
the jump. The electron does not remain on the higher orbit and returns to its lower
energy orbit releasing the extra energy as radiation.
Bohr’s model answered many scientific questions in its time though the model itself is
oversimplified and, in the strictest sense, incorrect. Electrons do
not orbit the nucleus like a planet orbiting the Sun; rather, they
behave as → standing waves. Same as
→ Bohr atom.
See also: → Bohr; → model.
