The mass of a proton is taken as one unit and its charge as plus one.
The mass of an electron is considered to be negligible and its charge is minus one.
The Structure of an Atom-- According to Dalton’s atomic theory the atom was indivisible and indestructible. But the discovery of two fundamental particles (electrons and protons) inside the atom, led to the failure of Dalton’s atomic theory. Then, It became necessary to know how electrons and protons are arranged within an atom. For explaining this, many scientists proposed various atomic models. J.J. Thomson was the first one to propose a model for the structure of an atom.
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