Predominantly discussed atomic models include the Rutherford Model, the Bohr Model and Chadwick's Model. Each of these models proposes various theories concerning an atom's structure, and successive models build upon the last to produce the modern perception of the atom.
The Rutherford Model asserted that the atom was composed of a infinitesimally small positively charged molecule, orbited by negatively charged electrons. Bohr's model took this concept further by proposing that electrons actually circled atoms in concentric rings, with electrons residing in different rings depending on energy level. The Chadwick Model takes from both the Rutherford Model and Bohr Model, but concludes that neutrally charged particles known as neutrons must also compose the atom.