Unit+2-+The+Atom


 * __The Atomic Theory__**

- All matter is made up of tiny particles called atoms. - Atoms cannot be created or destroyed by ordinary means. - Atoms are made up of a positively charged nucleus (which is made up of protons and neutrons) with orbiting electrons (which have a negative charge). - Atoms of one [|element] have identical properties. - Atoms of different elements have different properties. - When two or more elements combine in a constant ratio, they form a new substance called a compound.

The Discoveries of the Atom

- John Dalton is the scientist credited with discovering the atom and having scientific proof that all matter is made up of atoms - JJ Thompson's [|Cathode Ray] Experiment proved that particles exist smaller than atoms; it discovered the electron - Ernest Rutherford discovered that the atom had a very small, but dense nucleus using his Gold-foil Experiment. In this process, he bombarded a piece of gold foil with electrons. He came to the conclusion that an atom has a nucleus because some of the electrons passed through, some were deflected, and others refracted (went through but changed direction) - This discovery disproved the Plum Pudding Model in which an atom was made of a random mixture of particles - Niels Bohr described the behaviour of electrons in the atom like the planets' orbit around the sun. His theory stated that electrons occupy distinct regions, called shells, and when these electrons absorb energy, they jump up an energy level. When the electron releases energy, it returns to what is called its ground state

This image shows the Plum Pudding model, theorized by Thompson. In this theory, it was believed that the atom was randomly made up of particles (electrons, protons, and neutrons)

This image shows the results of Rutherford's Gold-Foil Experiment. It shows the paths of the electrons. In it you can see that some os the electrons went straight through, while others reflected or refracted. This lead to the conclusion that the atom has small and dense nucleus. (Nucleus is represented by the small, pink ball in the centre)



This is an illustration of the Bohr Planetary Model. The nucleus is located in the centre and the electrons are located around it, in their shells. The electrons orbit around the nucleus.

To get a closer look at the atom click [|HERE].