The History Of The Atom Flashcards
What was the name of the scientist who at the start of the 19th century described atoms as solid spheres and said that different spheres made up the different elements.
The scientist name was John Dalton
What did J J Thomson conclude from his experiments done in 1897
He concluded that atoms weren’t solid spheres, his measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles called electrons. He also came up with a new theory know as the plum pudding model.
What did the plum pudding model show
The plum pudding model showed the atom as a ball of positive charge with electrons stuck in it.
How did Rutherford show that the plum pudding model was wrong
Ernest Rutherford and Ernest Marsden conducted the alpha particle scattering experiments. They fired positively charged alpha particles at an extremely thin sheet of gold. From the plum pudding model they were 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. Whilst most of the particles did follow this rule, some were deflected more than expected and a small number were deflected backwards. So the plum pudding model couldn’t be right, so Rutherford came up with an idea to explain what had happened,the nuclear model of the atom.
What does Bohr’s model explain
Scientists realised that electrons in a “cloud” around the nucleus of an atom as Rutherford described would be attracted to the nucleus, causing the atom to collapse. Neils Bohr’s nuclear model of the atom suggested that all neutrons were contained in shells. Bohr proposed that electrons orbit the nucleus in fixed shells and aren’t anywhere between. Each shell is a fixed distance from the nucleus. Bohr’s theory of atomic structure was supported by many experiments and it helped to explain lots of other scientists observations at the time.
Who conducted further experiments and what did they find
Further experiments by Rutherford and other scientists showed that nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus. These particles are called protons. James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus which are called neutrons. This lead to a model of the atom which is pretty close to the one scientists use today.
