Section 1.3 History of the Atom Flashcards
John Dalton
Early 1800s
From his experiments, he suggested that substances were made up of atoms that were like tiny, hard spheres.
He also suggested that each element had its own atoms that differed from the others in their masses.
He believed that these atoms cannot be divided or splitted and only rearranged themselves and combined with other atoms in new ways.
J.J. Thomson
End of the 1800s
He discovered the electron, which had a mass of about 2000 times smaller than the lightest atom
He experimented on beams of particles and notices that they were attracted to a positive charge
He created the plum pudding model (electrons embedded in a cloud of positive charge)
Ernest Rutherford
1911
He experimented with radioactive particles by firing positive charged particles at the thinnest piece of gold foil they could make.
He said that the positive charge is concentrated at the centre with electrons orbiting around it
Niels Bohr
1914
He suggested that the electrons must be orbiting the nucleus at set distances (in energy shells)
How did scientists discover neutrons?
Evidence for protons and electrons were clear due to their charge, however there was a missing mass in atoms. Scientists then concluded that neutron exists and have no overall charge. It was James Chadwick (1932) who discovered neutrons.
