-
370 BCE
Demokritos theorises tiny indivisible particles
Demokritos thought that all matter must be made of incomprehensibly small pieces that couldn't be made any smaller. There was no easy way to develop this idea or communicate it at the time, so this theory went undeveloped for ~2170 years. -
Dalton discovers atoms
John Dalton dicovered that the tiny indivisible particles Demokritos talked about were in fact real, and were tiny spheres which he called atoms. He knew that they came in different types, or elements and that different elements could be combined together to make compounds. -
JJ Thompson discovers electrons
JJ Thompson did an experiment which led him to believe that atoms were made of a positive mass with negative "electrons" spread evenly throughout. We now know this to be false, but his theories on electrons were true. -
Rutherford discovers the nucleus and electron shells
Rutherford suggested that an atom is mostly empty space, with the electrons not being arranged around a central object called a nucleus. Rutherford came to this conclusion after an experiment that involved the firing of radioactive alpha particles particles through thin gold foils and detecting the alpha particles. Rutherford found that approximately 1 in 8000 were deflected so most of the atom is made up of empty space. -
Bohr discovers electron shells
Niels Bohr discovered electron shells in 1913 when he realised that if Rutherford's model was accurate, the electromagnetic field generated by the electrons would make them spiral into the nucleus and collapse the atom within 16 picoseconds, meaning that all atoms would be unstable. This was obviously incorrect, so Bohr fixed that.
