Democritus was the first to answer the question of "what is stuff?", in 440 BCE. He proposed that everything in the world was made up of tiny particles, surrounded by empty space. He speculated that they very in size and shape depending on the substance they compose which he called them particles 'atomos'.
In 1808, a quaker teacher named John Dalton, challenged this theory, although Democritus's idea was pure theory, Dalton showed that common substances always broke down into the same elements in the same portions. He concluded that the compounds were combinations of atoms of different elements
In the year of 1897, a physicist J.J Thompson, discovered electrons. He showed atoms as uniformly packed spheres of positive matter, built with negatively charged electrons. Yet his model of the atom didn't stick around long.
Rutherford became known as the father of the nuclear age. He shot small, positively charged alpha particles at a piece of gold foil. Thompsons theory did not work out as it would be like particles punching through a screen. Rutherford concluded that atoms consisted largely of empty space with just a few electrons while most of the mass was concentrated in the centre which he named the Nucleus.
In 1913, another of J.J Thompsons students, Niels Bohr, expanded on Rutherford's Nuclear model. He thought that electrons orbited the Nucleus at fixed energy's and distances. His planetary model took centre stage, but it ran into a few problems.
Werner Heisenberg showed that it was impossible to determine both the exact position and speed of electrons, as they moved around the atom.