Arguably the founding figure of the atomic theory. Democritus begins to theorise somewhere in 400BC that all matter is made up of miniature "atoms" which are not visible to the naked human eye.
Nuclear Model Developed by Ernest Rutherford
In 1803, following Democritus' theory, John Dalton created the first atomic model named the 'Solid Sphere Model' and also defines the atom as indivisible (this is later proven false)
Planetary Model Made by Niels Bohr
In 1904, Physicist JJ Thomson makes a giant stride in the study of the atom theory. He discovered the existence of electrons. As a result, Thomson went on to portray the 'Plum Pudding Model'. Which shows the prevalence of electrons scattered around a positive charge.
Quantum Model As Shown by Erwin SchrÖdinger
In 1911, with sufficient evidence, Ernest Rutherford showed that an atom is composed of concentrated energy in the centre (what we now know as the nucleus) To prove this, Earnest fired positively charged alpha particles at a sheet of gold foil. While most passed through without deflection - some deflected at large angles. Meaning that atoms have concentrated energy in the centre as shown in his Nuclear Model
With a modification of Ernest's atomic model, in 1913, Niels Bohr states that the electrons (as discovered by JJ Thomson) move in constant orbits of fixed sizes and energies around the nucleus (as discovered by Ernest Rutherford). This statement is depicted in his Planetary atomic model.
The most recent and most widely accepted theory of the atomic structure comes from SchrÖdinger who in 1926, makes the correction to Niels Bohr's theory. He explains how electrons move in waves around the nucleus rather than in set paths as stated by Niels. Using this knowledge. It shows that electrons can be found in clouds called orbitals. Which show an approximate location of electrons.