The atomic-molecular structure of matter began to be actively studied by Lomonosov. For the first time, a Russian scientist applied in chemistry a theory whose essence was reduced to certain provisions.
- All substances include “corpuscles”. Lomonosov called molecules this term.
- The corpuscles are made up of "elements." This term Lomonosov used to refer to atoms.
- All particles (both atoms and molecules) are continuously moving. The thermal state of all bodies is the result of the movement of their constituent particles.
- The same atoms are molecules in simple substances, various atoms are molecules in complex substances.
Atomistic teaching was subsequently applied by Dalton. The basis of the theory of the English scientist, characterizing the structure of matter, repeats the theory of Lomonosov. However, Dalton somewhat developed it. An English scientist tried to determine the atomic masses of elements known at that time. At the same time, Dalton denied the presence of molecules in simple substances, arguing that a simple substance contains only atoms. While complex elements include "complex atoms".
The doctrine of the atomic-molecular structure of substances was finally established only by the middle of the 19th century.
A molecule is called the smallest particle of a substance. It has all the chemical properties of an element. Atom is the smallest particle included in the composition of molecules of complex and simple substances. The composition of the atom determines the chemical properties of the elements. According to this provision, the modern definition of the smallest particle follows. Thus, an atom is an electrically neutral particle. It consists of a nucleus charged positively and electrons charged negatively.
In accordance with modern concepts, molecules make up vaporous and gaseous bodies. In solids, the smallest particles (molecules) are present subject to the presence of a crystal lattice, which, in turn, has a molecular structure.
There are several basic teachings.
A theory explaining the structure of matter indicates the presence of certain gaps between particles. The dimensions of these distances depend on the temperature and the state of aggregation of the object. The largest gaps between the molecules are observed in gaseous bodies. This determines the ability of gases to compress easily. The distance between the molecules in liquids is much smaller, so they are more difficult to compress. Solids practically cannot be compressed, due to the fact that the gaps between the particles are small.
Molecules are constantly in motion. The higher the body temperature, the higher the speed of movement. Between particles there are forces of mutual repulsion and attraction.
Molecules contain atoms that are also continuously in motion.
One type of atom is different from the other in properties and mass.
Solid molecular substances have crystal lattice sites that include molecules. The bonds between the particles are weak and break when heated. Therefore, such bodies have low melting points.
Bodies may have another structure. Substances can consist of atoms and other particles that make up the nodes of crystal lattices (for example, in iron, other metals). There are very strong bonds between these particles. To destroy them, you need to spend a lot of energy. This structure of the substance assumes a high melting point.
Based on the teachings, many phenomena are explained. For example, diffusion. This process is based on the ability of particles, molecules, atoms to penetrate into the gaps present between atoms or molecules in another substance. This, in turn, is possible due to the constant movement of the particles that make up the body.