History of the atom

• The first major theory that tried to explain what stuff is made out of was atomic theory, which states that everything is made up from tiny little particles that can't be broken down any further and that they're separated from each other by empty space.
• The idea of atomic theory was originally proposed by a Greek philosopher named Democritus, who was alive around 500 BC.
• It took another 2,300 years before anyone improved on Democritus's ideas.
• John Dalton described atoms as solid spheres and suggested that different types of spheres might make up the different elements.
• In 1897, J.J Thomson came up with the plum pudding model, which was based on his experiments that showed that the atoms couldn't be solid spheres and instead must have contained negatively charged particles, which we now know to be electrons.
• Ernest Rutherford and his students made a big discovery in 1909 when they fired positively charged alpha particles at a really thin sheet of gold.
• If the positive charge in the gold atoms was generally spread out as J.J Thomson had proposed with his plum pudding model, then the alpha particles should pass right through the sheet of gold because the weak spread out positive charge wouldn't be strong enough to affect them.
• The orbiting of the electrons is what prevents the atom from collapsing.
• A short while later, a guy called James Chadwick provided evidence for neutral particles in the nucleus which we now call neutrons.
• Further experiments by Rutherford found that the positive charge in the nucleus is actually made up of small discrete particles which we now know as protons.
• Rutherford suggested his nuclear model which proposed that there was a nucleas in the middle of the atom surrounded by electrons
• In 1913, Niels Bohr suggested a solution to Rutherford's problem, he suggested that the electrons orbited the nucleus in a similar way to how the planets orbit the sun and also that they were held in shells.
• Many experiments have supported Niels Bohr's model and it's pretty much the same one as we follow today with just a few small changes.
• Rutherford thought that the alpha particles would go through and some would deflect but some went through , more thank expected some deflected and some even deflected backwards.