Contributions to the development of Models of the Atom Ernest Rutherford

Previous model Thomson “Plum Pudding” Model: atoms have negative charges evenly distributed throughout the atom’s positive interior. PROBLEM: There was NO experimental evidence to show where the positive charge was located within the atom

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Testing Thomson’s model If Thomson’s model was correct then the alpha particles should have gone straight through the atom with little deflection

Rutherford’s Gold Foil Experiment 99% of alpha particles went straight through the gold foil. But, 0.5% deflected, and 0.5% reflected!

"...it was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you..." said Rutherford, 1936.

Rutherford’s Conclusions The ‘Plum Pudding’ model was wrong. An atom basically consists of a lot of empty space!

Rutherford’s Conclusions All of an atom’s positive charge is concentrated in a very small core at the atom’s center, which Rutherford called the nucleus. The negatively charged electrons move around the nucleus.

Rutherford’s Conclusions Also noted that if the entire atom is the size of a football stadium, the nucleus would be about the size of a marble sitting on the 50-yd line. Hundred times smaller than shown

Additional findings… The atom consisted of a nucleus: size 10-15 to 10-14 meter The nucleus contains the whole positive charge and almost the whole atom's mass. Around the nucleus, on the area of the size of the order of 10-10 meter, electrons are circling. Electrons have to circle around the nucleus on orbits, not to fell down on the nucleus. The orbits depend on electrons energy.

Bio Pioneer in nuclear physics: he discovered (and named) alpha and beta radiation, named the nucleus and proton and won the 1908 Nobel prize in chemistry for explaining radioactivity as the disintegration of atoms. Rutherford's description of an atomic structure with orbital electrons became the accepted model (with further help provided by his student and colleague, Niels Bohr), and in 1920 he predicted the existence of the neutron, which was later discovered by James Chadwick.

Bio from New Zealand's South Island, he spent most of his professional career overseas at McGill University in Montreal, Canada (1895-98), and at Manchester University (1898-1907) and Cambridge University (1919-37) in the United Kingdom. Rutherford was knighted in 1914, served as president of the Royal Society from 1925-30, and in 1931 was named Ernest, Lord Rutherford of Nelson (New Zealand).

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