The first one who did/said

1. Dalton

1.1. stated the first theory about the atomic structure.

1.2. Atoms of the same element are identical.

1.3. Atoms of different elements are different.

1.4. Law of Constant Ratios:

2. Thomson

2.1. Discovered the cathode rays

2.2. Carried out many experiments on the electric discharge through gases.

2.3. the atom electrically neutral.

3. Rutherford

3.1. the first atomic model on experimental Basis.

3.2. the Gold-Foil Experiment (Alpha rays).

3.3. the atom not a solid sphere

3.4. The atom structure resemble the solar system.

3.5. Discovered the nucleus. (+ve charged)

3.6. Electrons revolve around the nucleus at high speed in special orbital .

4. Bohr

4.1. the first scientist who explained atomic spectra of H2.

4.2. definite allowed energy levels.

4.3. the principle quantum number (n)

4.4. (quantum)

4.5. The spectral lines indicate the energy levels from which their electrons are transmitted back to the ground state.

5. modern atomic theory

5.1. De Broglie

5.1.1. The dual nature of electron.(Wave and Particle).

5.2. Heisenberg

5.2.1. Uncertainty principle.(velocity and position of an electron).

5.3. Schrödinger

5.3.1. The wave-mechanical theory of atom.

5.3.2. "the electron cloud " "Orbitals"