In nature, very many atoms exist in bound form, forming special associations called molecules. However, inert gases, justifying their name, form monatomic units. The molecular structure of a substance usually implies covalent bonds. But there are so-called conditionally weak interactions between atoms. Molecules can be huge, made up of millions of atoms. Where does such a complex molecular structure occur? Examples are many organic substances, such as quaternary proteins and DNA.
No chemistry The covalent bonds that hold atoms together are extremely strong. But the physical properties of the substance do not depend on this, they depend on the van der Waals forces and hydrogen bonds, which ensure the interaction of neighboring fragments of structures with each other. The molecular structure of a liquid, gas, or fusible solid substance also explains the state of aggregation in which we observe them at a certain temperature. In order to change the state of a substance, simply heat it or cool it. Covalent bonds are not broken at the same time.
Boundaries of the beginning of processes
How high or low will the gas and melting points be? It depends on the strength of intermolecular interactions. Hydrogen bonds in a substance increase the temperature of the change in the state of aggregation. The larger the molecules, the more Van der Waals interactions in them, the more difficult it is to make a solid liquid or liquid gas.
Ammonia features
Most known substances in water are not soluble at all. And those that nevertheless dissolve enter into interaction, often with the formation of new hydrogen bonds. An example is ammonia. It is able to break down hydrogen bonds between water molecules and successfully build its own. In parallel, there is an ion exchange reaction, but it does not play a large role in the dissolution of ammonia. Basically, ammonia owes this process to hydrogen bonds. The reaction proceeds in both directions, the process can be in equilibrium in general at certain temperature and pressure. Other soluble substances, such as ethanol and sugars, also bind perfectly with water through intermolecular interactions.
Other reasons
Solubility in organic liquids is ensured by the formation of van der Waals bonds. The intrinsic solvent interactions are destroyed. A soluble substance binds to its molecules, forming a uniform-looking mixture. Very many vital processes became possible due to these properties of organic substances.
Toku - no
Why don't most substances conduct electricity? The molecular structure does not allow! Current requires the simultaneous movement of a large number of electrons, a kind of "collective farm" of them. This happens with metals, but non-metals almost never happen. At the boundary, in relation to this property, there are semiconductor materials having medium-dependent electrical conductivity.
Very many physical processes are easily explained if there is information about the molecular structure of a given substance. Aggregate states are well studied by modern physics.