atomic structure

atomic structure

1. when was it discovered?

   • John Dalton published his ideas about atoms in 1803. He thought that all matter was made of tiny particles called atoms, which he imagined as tiny spheres that could not be divided.

2. when was the electron discovered and who by?

   • Nearly 100 years later, J J Thomson carried out experiments and discovered the electron. This led him to suggest the plum pudding model of the atom. In this model, the atom is a ball of positive charge with negative electrons embedded in it - like currants in a Christmas pudding.

3. the plum pudding model

   • In 1909 Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, positively charged alpha particles were fired at thin gold foil. Most alpha particles went straight through the foil. But a few were scattered in different directions
     • This evidence led Rutherford to suggest a new model for the atom, called the nuclear model. In the nuclear model: the mass of an atom is concentrated at its centre, the nucleus the nucleus is positively charged

4. Developing models of atoms

   • Niels Bohr adapted Ernest Rutherford's nuclear model. Bohr did calculations that led him to suggest that electrons orbit the nucleus in shells. The shells are at certain distances from the nucleus. The calculations agreed with observations from experiments.

5. Structure of the atom

   • Nucleus and shells An atom has a central nucleus. This is surrounded by electrons arranged in shells. The nucleus is tiny compared to the atom as a whole: the radius of an atom is about 0.1 nm (1 × 10-10 m) the radius of a nucleus (1 × 10-14 m) is less than \frac{1}{10,000} of the radius of an atom For comparison, the radius of a typical bacterium is 1 × 10-6 m and the radius of a human hair is about 1 × 10-4 m

Imagens e arquivos do mapa