What happens if everything is made of tiny elements and that two of the same substance would always be broken down into the same elements?
I am going to shoot a negative ray through some metal plates and see what happens. Oh, now I have discovered the electron and so I am going to show it as a Plum Pudding.
Just like my crazy teacher I am going to shoot positively charged alpha rays at foil. Turns out my teacher is wrong and that there is space in an atom.
Democritus challenged the elemental theory in 440 BCE and said that everything was made up of tiny particles which were indestructible. He called them 'Atomos'. John Dalton in 1808 revived the idea of this model adding that all substances were made up of elements and that two of the same substance will always be made up of the same elements.
What Happens if the Electrons Orbit The Nucleus rather than just having space in between?
Using the Cathode Ray Tube experiment J.J Thomson concluded that there must be positive and negative particles in the atom. He created a model of this in the 'Plum Pudding Model' where the raisins represent the electrons and the dough represents the protons. This was discovered in 1897.
What happens if atoms don't orbit but are completely random. I will just hit it with some gamma rays and see. Wow! I was right.
In 1911, Ernest Rutherford discovered that the model his teacher had created was wrong. This was discovered because he wanted to learn more about atoms and so shot gold foil with positively charged alpha rays. Some went through, like the previous model suggested, but others deflected. This led to him concluding that there was space in atoms. He called the dense centre the nucleus.
In 1913, Niels Bohr stipulated that electrons must orbit the nucleus and be able to jump orbits but not exist in between. They had to orbit at fixed energy levels as well. This was discovered when he realised that Rutherford's model was too unstable due to mechanics and electromagnetic theory and that the electrons would release radiation causing them to lose their charge over time.
In 1925 Heisenberg creates the quantum theory. He states that electrons don't orbit but actually have areas which electrons are more likely to reside. He discovered this idea through mathematical calculations but also a gamma ray microscope. His mathematical calculations showed that you could never predict where an atom could be or its velocity at that point.