Bohr بؤر Bohr
*Fr.: Bohr*
Niels Bohr (1885-1962), Danish physicist who made several important
contributions to modern physics. He won the 1922 Nobel prize for physics
in recognition of his work on the structure of atoms. |

Bohr atom اتم ِ بؤر atom-e Bohr
*Fr.: atome de Bohr*
The simplest model of an atom according to which electrons move
around the central nucleus in circular, but well-defined, orbits. For more details
see → *Bohr model*. → *Bohr*; → *atom*. |

Bohr magneton مگنتون ِ بؤر magneton-e Bohr (#)
*Fr.: magnéton de Bohr*
A fundamental constant, first calculated by Bohr, for the intrinsic
→ *spin magnetic moment* of the electron.
It is given by: *μ*_{B} = eħ/2*m*_{e} =
9.27 x 10^{-24} joule/tesla = 5.79 x 10^{-5} eV/tesla,
representing the minimum amount of magnetism which can be caused by the revolution
of an electron around an atomic nucleus. It serves as a unit for measuring the
magnetic moments of atomic particles. → *Bohr*; *magneton*, from → *magnet*
+ → *-on*. |

Bohr model مدل ِ بؤر model-e Bohr
*Fr.: modèle de Bohr*
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 *h*ν = ε_{1} - ε_{2},
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 wave*s. Same as
→ *Bohr atom*. → *Bohr*; → *model*. |

Bohr radius شعاع ِ بؤر šo'â'-e Bohr
*Fr.: rayon de Bohr*
The radius of the orbit of the hydrogen electron in its ground state
(0.529 Å). → *Bohr*; → *radius*. |

Bohr's first postulate فراوس ِ نخست ِ بؤر farâvas-e naxost-e Bohr
*Fr.: premier postulat de Bohr*
One of the postulates used in the → *Bohr model*, whereby
there are certain steady states of the atom in which electrons can only travel in stable orbits.
In spite of their acceleration, the electrons do not radiate electromagnetic
waves when they move along stationary orbits. → *Bohr*; → *first*;
→ *postulate*. |

Bohr's postulate فراوس ِ بؤر farâvas-e Bohr
*Fr.: postulat de Bohr*
One of the three postulates advanced in the → *Bohr model*
which led to the correct prediction of the observed line spectrum of hydrogen atom.
See also → *Bohr's first postulate*,
→ *Bohr's second postulate*,
→ *Bohr's third postulate*, → *Bohr*; → *postulate*. |

Bohr's second postulate فراوس ِ دوم ِ بؤر farâvas-e dovom-e Bohr
*Fr.: deuxième postulat de Bohr*
One of the postulates used in the → *Bohr model*, whereby when an atom is
in the steady state an electron travelling in a circular orbit should have
→ *quantized* values of the
→ *angular momentum* which comply with
the condition *p = n(h/2π)*,
where *p* is the angular momentum of the electron, *h* is
→ *Planck's constant*, and *n* is a positive integer called
→ *quantum number*. → *Bohr*; → *second*;
→ *postulate*. |

Bohr's third postulate فراوس ِ سوم ِ بؤر farâvas-e sevom-e Bohr
*Fr.: troisième postulat de Bohr*
One of the postulates used in the → *Bohr model*, whereby the
atom emits (absorbs) a quantum of electromagnetic energy
(→ *photon*) when the electron
passes from an orbit with a greater (lesser) *n* value to one with a lesser
(greater) value. The energy of the quantum is equal to the difference
between the energies of the electron on its orbits before and after the transition
or "jump": *h*ν = ε_{1} - ε_{2}, where
*h* is the → *Planck's constant* and ν the
frequency of the transition. → *Bohr*; → *third*;
→ *postulate*. |