Atomic
structure
Atoms structure
has undergone a chronological change from time to time in line with the
discoveries and sophistication in the field of science.
The first proposed
structure of an atom was called plum pudding, this was proposed by J.J Thompson
in 1904 after he discovered the electron, and the model established that atoms
consist of electron in a fluid of positive charges to balance the atom. This model
was proposed before the discovery of the nucleus. According to the model the
electrons are positioned throughout the atom and they are called the plums
while it is balanced by a positive charge called the pudding.
The above model
was disapproved after the discovery of the nucleus and hence the planetary or Rutherford
model of the atom was established, in this model the atom are believed to
consist of a centrally located nucleus surrounded by a cloud of orbiting
electrons, this model was proposed by sir Ernest Rutherford shortly after an
experiment carried out by Ernest Marsden and Hans Geiger.
A beam of
alpha particles were passed through a
thin film of gold foil, more than
90% of the beam pass through the atom unaltered , only fem at the center that
were distorted; some are deflected through an angle and some are returned. This
experiment led to the discovery of the atomic nucleus and hence a modification to
the atomic structure.
According to
the model the atom consist of a centrally located nucleus, positively charged
and massive, the atom is almost empty, with just the nucleus at the centre and
an electrons orbiting at the edges.
The Rutherford atomic model was found to be insufficient
because of some limitations, it fail to explain how an electron can maintain a
stable orbit. The motion of electrons in the Rutherford atom is unstable because
according to electromagnetic and classical
theory ; any charge particle moving a curved
path emit radiation, therefore the electrons orbiting the nucleus will lose
energy and be captured by the nucleus.
In 1913, sir
Neil bohr proposed another model for the structure of the atom, he reaffirm the
planetary nature of the Rutherford model but added that electrons only radiate
energy when they translate form one orbit to another and return back, when an
electrons get excited and jump from its ground state to a higher energy level,
and return back to their original orbit, they will lose the energy they gain. This
energy is lost inform of radiations, this means that electrons only emit the
difference between the two energy level.
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