Answer:
He discovered the electron - J.J Thompson
He discovered periodic changes in properties of elements when they are listed in order of their atomic weights - Dimitri Mendeleev
He experimented with the deflection of cathode rays by a magnetic field - J.J Thompson
He carried out experiments that measured the scattering of alpha particles by heavy atoms - Ernest Rutherford
His model of the hydrogen atom led to an accurate calculation of the wavelengths of light emitted by an excited hydrogen atom - Neil Bohr
He proposed the planetary model of the atom with most of the mass of the atom concentrated in a very small nucleus - Ernest Rutherford
He modified the planetary model of the atom by suggesting electrons could travel about the nucleus in only a few discrete stable orbits - Neil Bohr
Explanation:
J.J Thompson discovered the electrons. He initially called them cathode rays and he also studied how they are deflected in magnetic fields and by so doing established that they are negatively charged particles.
Ernest Rutherford is renowned for his experiment using the thin gold foil and alpha particles to determine that atoms have a positively charged massive core called the nucleus. This led to the proposition of the planetary model of the atom.
Dimitri Mendeleev discovered periodic changes in properties of elements when they are listed in order of their atomic weights. This led to the discovery of the Mendeleev periodic table.
Neil Bohr model of the atom gave accurate explanation of the emission spectra of the hydrogen atom. His atomic model suggested that electrons could travel about the nucleus in only a few discrete stable orbits.
