The History of the Atom Flashcards
How did we prove that the Plum Pudding Model was wrong?
Rutherford conducted Alpha particle scattering experiments. They fired positively charged alpha particles at an extremely thin sheet of gold.
From the Plum Pudding Model, Rutherford was expecting the particles to pass straight through the sheet or be slightly deflected at most. This was because the positive charge of each atom was thought to be very spread out through the ‘pudding’ of the atom. But, whilst most of the particles did go straight through the gold sheet, some were deflected more than expected, and a small number were deflected backwards. So the Plum Pudding model couldn’t be correct.
So what did Rutherford conclude with?
Rutherford came up with an idea to explain this new evidence - the nuclear model of the atom. In this, there’s a tiny, positively charged nucleus at the centre, where most of the mas is concentrated. A ‘cloud’ of negative electrons surrounds the nucleus - so most of the atom is empty space. When alpha particles came near the concentrated, positive charge of the nucleus, they were deflected. If they were fired directly at the nucleus, backwards. Otherwise, they passed through the empty space.
What did Bohr’s Nuclear Model suggest? And what did Bohr Propose?
Niels Bohr’s Nuclear Model of the Atom suggested that all the electrons were contained in shells.
Bohr proposed that electrons orbited the nucleus in fixed shells and aren’t anywhere in between. Each shell is a fixed distance from the nucleus.
Further Experiments showed the Existence of Protons and Neutrons!
Rutherford and others, later, showed that the nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus. These particle were names protons.
20 years later, James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus which are now called neutrons.
