What are the parts of an atom?

A series of experiences made in the nineteenth century and early twentieth century, which led to the discovery of the electron, the cathode rays, the
X-rays, radioactivity showed that the atom, contrary to the name significance (atoms in Greek means indivisible), can not be considered  as a unitary particle, but as a complex system made up of other  masses less parts, some charged, others neutral.In 1904, J.J. Thomson proposed the first model of the atom: he conceives atom as a positively charged sphere, inside which electrons are distributed in symmetrical fashion. The static model of the atom was available by that 
time, being replaced later by that of Rutherford, as it
could explain many of the properties of the atom.

Rutherford proposed the nuclear model of the atom in 1912, saying that in center atom is a very small core-loaded with positive electricity,where almost the entire mass of the atom is concentrated  and around which rotate on circular orbits at certain distances, negative charged particles electrons, like planets revolving around the Sun. After conceptualisations
Rutherford knew, most of the atomic volume is empty,electrons  are animated by a continuous circular motion on orbit and they are maintained in balance due to centrifugal force balanced by the force of attraction between the positive nucleus and negative electrons. According to Rutherford's model, the atom of any element consists of two distinct parts:
-a central system called the kernel,
-outside of kernel, a part called the electronic shell

Atomic nucleus, although it is around the 10,000th of the atom diameter , contains almost the entire mass of the atom. It consists of several kinds of elementary particles from which,for the chemistry problems that we're
interested, we'll retain only:
- Protons - material particles  loaded with one electric elementary positive charge and whose mass is equal approximately to unity atomic mass (1.00727 0.000003 u.a.m.) and
- Neutron - neutral material particles, which also have the mass roughly equal  with atomic mass unit (1.00866).
For protons and neutrons, as part of the kernel, is used today the name nucleons, name justified by possible nuclear transformations: neutron =proton + electron, which means that the two particles would have two different quantum states of the same particles - nucleons.