Bohr Model of the Atom

why is the nucleus of an atom positively charged

By Anne Marie Helmenstine, Ph.D. Chemistry Expert

Anne Helmenstine, Ph.D. is an author and consultant with a broad scientific and medical background. Read more

The Bohr Model has an atom consisting of a small, positively-charged nucleus orbited by negatively-charged electrons. Here's a closer look at the Bohr Model, which is sometimes called the Rutherford-Bohr Model.

Overview of the Bohr Model

The modern model of the atom is based on quantum mechanics. The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without all of the high-level math of the modern version. Unlike earlier models, the Bohr Model explains the Rydberg formula for the spectral emission lines of atomic hydrogen .

The Bohr Model is a planetary model in which the negatively-charged electrons orbit a

small, positively-charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar).

The gravitational force of the solar system is mathematically akin to the Coulomb (electrical) force between the positively-charged nucleus and the negatively-charged electrons.

Main Points of the Bohr Model

  • Electrons orbit the nucleus in orbits that have a set size and energy.
  • The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.
  • Radiation is absorbed or emitted when an electron moves from one orbit to another.

Bohr Model of Hydrogen

The simplest example of the Bohr Model is for the hydrogen atom (Z = 1) or for a hydrogen-like ion (Z > 1), in which a negatively-charged electron orbits a small positively-charged nucleus.


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