Bohr Model

The most important properties of atomic and molecular structure may be exemplified using a simplified picture of an atom that is called the Bohr Model.This model was proposed by Niels Bohr .

The Bohr Model is also known  as the “planetary model” .For example,it is used as a symbol for atomic energy. The energy in “atomic energy” is actually the energy of the nucleus, rather than the entire atom. In the Bohr Model the neutrons and protons  occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun . The adjacent image is not to scale since in the realistic case the radius of the nucleus is about 100,000 times smaller than the radius of the entire atom, and as far as we can tell electrons are point particles without a physical extent.

planatery motion

This similarity between a planetary model and the Bohr Model of the atom ultimately arises because the attractive gravitational force in a solar system and the attractive Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons in an atom are mathematically of the same form. (The form is the same, but the intrinsic strength of the Coulomb interaction is much larger than that of the gravitational interaction; in addition, there are positive and negative electrical charges so the Coulomb interaction can be either attractive or repulsive, but gravitation is always attractive in our present Universe).

atomic model


Electrons are the smallest and lightest of the particles in an atom. Electrons have a negative charge, which means that they seem to be surrounded by a kind of invisible force field. This is called an electrostatic field.It has a constant circular motion around the nucleus of that atom.


Protons are much larger and heavier than electrons. Protons have a positive electrical charge. This positively charged electrostatic field is exactly the same strength as the electrostatic field in an electron, but it is opposite in polarity.

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