The Development Of The Model Of The Atom

What is the order of scientists who contributed to the development of the model of the atom?

John Dalton, JJ Thomson, Rutherford, Niels Bohr, James Chadwick

What was John Dalton's theory?

-that matter was made up of tiny spheres (atoms) that couldn't be broken up
-each element was made up of a different type of atom

What was JJ Thomsons theory?

-discovered particles called electrons that could be removed from atoms (wasn't right)
-suggested atoms were spheres of positive charge with tiny negative electrons stuck in them: plum pudding model

What was Ernest Rutherford's experiment?

-fired a beam of alpha particles at thin gold foil: alpha scattering experiment
-expected particles to pass straight through the gold sheet or only be slightly deflected
-most particles went straight through but some were deflected more than expected and a few were deflected back

What did Ernest Rutherford's experiment discover?

-because some were deflected he discovered most of the mass of the atom was concentrated in the centre in a tiny nucleus
-nucleus must have a positive charge because it repelled the positive alpha particles
-nearly all particles went straight through so atom must be mostly empty space
-first nuclear model of the atom

What was Niels Bohr's theory?

-the nuclear model from the alpha scattering experiment was a positively charged nucleus surrounded by a cloud of negative electrons
-that electrons are orbiting the nucleus at certain distances called energy levels
-nucleus made up of a group of particles (protons) with the same positive charge that added up to the overall charge of the nucleus

What did James Chadwick discover?

the neutron which explained the imbalance between the atomic and mass numbers