History of the Periodic Table Flashcards
What did Democritus do?
First proposed everything was made of tiny particles surrounded by empty space. His idea was opposed at the time
What did John Dalton do?
Showed that common substances always broke down into the same substances in the same proportions. Various compounds are combinations of atoms of different elements, each of a particular size and mass (can’t be created or destroyed)
What did J.J. Thompson Do?
Discovered the electron, showing it through the plum pudding model - atoms were uniformly packed spheres of positive matter filled with negatively charged electons.
What did Ernest Rutherford do?
Was studying the effects of X-rays on gases - and decided to study atoms as well, by shooting small positively charged alpha particles at a gold sheet of foil. Most of the particles went through, but some bounced back. He concluded that atoms were mainly space with a few electrons, with most of the mass at the centre - the “nucleus”
What did Niels Bohr do?
Said that electrons orbit the nucleus at fixed energies and distances, able to jump from one level to another, but not in the spaces between.
What did Werner Heidenberg do?
Created the uncertainty principle, determined it was impossible to determine the exact position and speed of electrons.
What’s the current model?
Quantum model - electrons cannot be pinpointed but exist within a range of locations.
