Dalton and avogadro founded atomism and molecular theory, and their knowledge taught us to look at the world from a microscopic perspective. Dalton's atomism and avogadro's molecular theory are both theoretical explanations of the composition of matter. According to their theory, some substances are made up of molecules or atoms.

/kloc-in the 9th century, the British scientist J. Dalton summed up many important experiences and laws in chemical changes with quantitative research methods, and put forward a scientific atomic hypothesis. Avogadro, an Italian scientist, introduced the concept of "molecule" on the basis of Grusack's law of French chemist, which supplemented and corrected the deficiency of Dalton's atomism, thus forming the theory of atoms and molecules.

The main points of atomism and molecular theory are as follows:

1, all substances are composed of molecules, and molecules are the smallest particles that keep the chemical properties of substances.

2. Molecules are composed of atoms. In chemical changes, atoms combine to form molecules, and molecules are decomposed into atoms, which are the smallest unit that cannot be subdivided.

3. Different kinds of atoms or molecules have different properties, weights and sizes.

Atoms and molecules are always in motion.