3.1.1.1 fundamental particles

what has happened to the model of atomic structure and why?

It has evolved over time due to changes in knowledge and scientific understanding

what was the model of the atom known as in 1897?

the ‘plum pudding model’

describe the ‘plum pudding model’

an atom that consisted of a sphere of positive charge, with small negatively charges distributed/embedded evenly within it

what experiment disproved the plum pudding model in 1909?

the Rutherford scattering experiment → positively charged alpha particles (He2+ ions) were fired at a very thin sheet of gold

explain why the Rutherford scattering experiment showed that the plum pudding model was incorrect

* if the ppm was correct, most alpha particles would be slightly deflected by the positive sphere
* however most of the particles passed straight through the gold without any deflection and a small number deflected backwards

what atomic model did the results of the scattering experiment result in and why?

* a small positively charged nucleus (some He2+ deflected backwards)
* surrounded by a cloud of negative electrons
* most of the atom is empty space (most He2+ passed straight through)

what are the differences between the current model and the plum pudding model?

the current model has

* a nucleus in the centre


* protons and neutrons in the nucleus
* electrons in shells

describe the current model of the atom

an atom consisting of a nucleus containing protons and neutrons surrounded by electrons

* nucleus has an overall positive charge + contains almost entire mass of atom
* atom has a neutral charge (electrons = protons)

what change did Bohr introduce to the atomic model (after the scattering experiment)?

he stated that electrons orbit the nucleus at fixed distances/energy levels

give the relative mass + relative charge for a proton, neutron + electron

Mass Charge

proton: 1 +1

neutron: 1 0

electron: 1/1840 -1