The number of electrons in the outer orbit determines the elements properties
Positively Charged Nucleus
Niels Bohr showed the atom as a small, positively charged nucleus surrounded by orbiting electrons. He also discovered that electrons travel in seperate orbits. It is questioned if Bohr was influenced by anyone through his discoveries
James Chadwick discovered that there are particles with no electric charge that, along with protons, make up an atoms nucleus, these particles are called neutrons. He made his discovery with influence from Rutherford's Atomic theory.
Otto Hahn, Lise Meitner, and Frtitz Strassman discovered nuclear fission together, by bombarding a uranium atom with neutrons, it eventually split. When atoms are split during nuclear fission, a large amount of energy is released