Dalton has been engaged in the study of atomic problems, and accumulated his main views on atomism through data, experiments and thinking. 1803 put forward the famous conclusion in September: ① atoms are very tiny and inseparable particles that constitute chemical elements. In chemical reactions, atoms keep their original properties. ② All the atoms of the same element have the same quality, but the atoms of different elements have different quality, and the quality of atoms is the most fundamental feature of each element. (3) When atoms of elements with simple numerical ratios combine, chemical reactions occur between them to form compounds, and the atoms of the compounds are called complex atoms. ④ When atoms of one element combine with atoms of another element, a simple number ratio is formed.

On June 265438+1October 2 1 day of the same year, Dalton reported his theory of chemical atomism and read out his second paper, the first relative weight table of the smallest particle of an object. His theory has aroused widespread concern in the scientific community.

After 1804, Dalton conducted an analysis experiment on the chemical composition of methane and ethylene. In this process, he discovered the law of multiple proportion: when two or more compounds are generated by the same two elements, if the mass of one element remains the same, the relative weight of the other element in the compound becomes a simple integer ratio. Dalton thinks that the law of multiples can be regarded as the inference and proof of atomism. From 65438 to 0807, Thomson introduced Dalton's atomism in detail in his book Chemical System.

In the second year, Dalton's main chemical work, A New System of Chemical Philosophy, was officially published, which recorded Dalton's main experiments and atomism theory in detail, and Dalton's atomism was officially published. Dalton's atomism has a solid scientific foundation, but there are new contradictions in the face of new experimental facts. Its biggest disadvantage is that the molecular formula of the compound must be determined according to the existence of the known compound in advance.

18 1 1 year, Italian scientist avogadro introduced the concept of molecule into atomic theory. He thinks that the particles that make up a gas are not atoms, but molecules. Simple materials's molecules are composed of the same kind of atoms; The molecule of a compound consists of several different atoms. Avogadro's hypothesis basically overcomes the shortcomings of Dalton's atomism. It can be said that Dalton's theory of atoms and molecules could not really be established without avogadro's supplement.

Compared with the previous atomic theory, this atomic and molecular theory supplemented by avogadro has made great progress. In the past, there was no transition between atoms and macroscopic substances, so it was very difficult to infer the properties of various substances from atoms. Now, different levels such as molecules and atoms have been found in the material structure. Therefore, we can think that people's understanding of how matter is constituted is close to the true nature of matter.