(N/A) The development of the atomic model progressed through several stages:
$1$. Thomson's Model: $J$.$J$. Thomson proposed that an atom consists of a positively charged sphere with negatively charged electrons embedded in it,similar to seeds in a watermelon. The total positive and negative charges are equal.
$2$. Rutherford's Model: Ernest Rutherford proposed that an atom has a tiny,positively charged central nucleus containing almost all the mass. Electrons revolve around this nucleus in circular paths.
$3$. Bohr's Model: Niels Bohr refined the model by proposing that electrons revolve in discrete,stable orbits without radiating energy.
Features of the presently accepted model (Bohr-Rutherford model):
$(i)$ The atom has a small,dense,positively charged nucleus at the center where the entire mass is concentrated.
$(ii)$ Electrons revolve around the nucleus in specific,well-defined circular orbits called discrete energy levels or shells,and they do not lose energy while moving in these orbits.