All atoms have the same mass

Student info: Dalton and his atomic model

It is strange that there are so many different pure substances that when they are chemically broken down (analysis), some (relatively few) substances always remain that cannot be further broken down into other substances (→ elements).
The English teacher and naturalist John Dalton (1766 to 1844) finally provided an explanation for this fact. Dalton conducted research in a wide variety of fields and became an important pioneer of chemistry as an exact natural science.
Dalton's most important contribution to science was his atomic theory. He postulated that the atom is the smallest indivisible unit of matter. "Elements consist of the same and indivisible particles, the atoms, which are characteristic for the respective element". According to his idea, there are not any number of different atoms (Democritus), but just as many different ones as there are elements. The atoms differ in their mass and size. Different atoms can be combined with one another through synthesis and separated again through analysis. Because only certain whole atoms can be united with each other in syntheses, the substances react with each other in a ratio of constant mass proportions.

The key messages of Dalton's atomic model :

  1. Every substance consists of the smallest, indivisible spherical particles, the atoms.
  2. All atoms of an element have the same volume and mass. The atoms of different elements differ in their volume and mass.
  3. Atoms are indestructible. They can neither be destroyed nor created by chemical processes.
  4. In chemical reactions, the atoms of the starting materials are rearranged and linked to one another in certain proportions

Of course, John Dalton couldn't see atoms either. His statements were model assumptions , which provided explanations for many observations. Many of his assumptions still hold up today. For example, scanning tunnel microscopes have been used to create images of atoms that show that atoms are actually spherical in shape. It is also true that atoms have a certain mass and a certain volume. It is also correct that the atoms are involved in chemical reactions

The assumption that atoms are the smallest particles and indestructible turned out to be a mistake.

task : Calculate the size (diameter) of a carbon atom.

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