Matter is discontinuous in nature (it does not repeat itself continuously). It is formed from elementary grains: atoms (the smallest possible particle of an element according to John Dalton 1807). 105 atoms or elements have been discovered, each designated by its name and symbol. For example: carbon C; nitrogen N; hydrogen H; oxygen O.
Atoms differ in their structure and mass, and are themselves fragmented into small particles: electrons, protons and neutrons, which are the same regardless of the substance or matter under consideration. The atom does not often exist in a free state; it combines with other elements to form molecules. There are diatomic molecules (H2, O2, NaCl.......) and polyatomic molecules (H2O, H2SO4, etc.).
- Enseignant: salima Samai