The structure of an atom have been described in different way by several scientists. Amony this scientist that have described an atom and contribute to discovery and development of its component include the following

1. Johh Dalton

2. Sir J.J Thompson

3. Ernest Rutherford

4. .R.A . Millikan

5. Niel Bohr

6. James Chadwick


DALTON'S ATOMIC MODEL

In the seventh century Democritus (Greek philosopher) defined am atom as the smallest indivisible particle of matter. In 1808 John Dalton (an english scientist) further expanded this definition by stating that atom was the smallest indivisible particle of an element, which can take part in the chemical reaction. He certainly up postulated some theory which is used in supporting his atomic definition. However, some of this theory were later on modify.

*Dalton's atomic theory/ modification*

1. He stated that am atom is the smallest indivisible particle of an element. 

               Modification

This statement no longer hold due to the discovery of sub-atomic particle such as proton, nuetron, and electrons which are particle smaller than the atom itself

2. He stated that atom can neither be created nor destroyed.

              Modification

This statement no longer hold because
atom can be created and by the process called radioactivity.

3. He stated that all the atom of a particle element were alike in every respect but different from atom of all other element.

                    Modification

This theory no longer hold due to the discovery of isotopes.



THOMPSON'S ATOMIC MODEL

J.J Thompson refer to his atomic model as the watermelon model or as the plum paddling model. According to hin, he said an atom was a sphere of positively charge particle in which negatively charge electron were embedded. This model was discarded as it was discovered that electrons were actually situated on the shell or orbit of am atom and not within the atom. J.J Thompson also discovered that protons and electrons are measured in their charge to mass ratio. The charges on an electron was measured by R.A . Millikan. James Chadwick discovered neutron while Henry Mosely coined the ferm atomic number. 
Niels Bohr worked on the electrical model of an atom while Ernest Rutherford accurately described an atom has been like a minuture solar system. He said that an atom was like a minature solar system with electron revolving round the necleus just like the planet revolve round the sun. He further explain that they was a force of attraction between the necleus and electron which kept the electron moving in a circular part around the nucleus. If this force of attraction is destroyed, the electron spiral on a straight into space.

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