Kinetic-molecular theory: the 3 states of matter

Solid, liquid and gaseous: what is it that makes these states of matter exist?

It is said that the entire universe is made up of matter and that when matter changes, energy is generated. And as is normal, the curious nature of human beings has led us to wonder on many occasions what all this matter is made of. Throughout history, different models have been devised to explain this, one of them being the kinetic molecular theory.

According to this model, the matter would be constituted by a fundamental unit that is not possible to be appreciated with the senses, I am speaking of the atom. In turn, atoms are grouped together to form molecules.

To give a classic example, the water molecule is structured with an oxygen atom and two hydrogen atoms (H2O). But the kinetic theory not only postulates this, but also because there are the three fundamental states of matter: solid, liquid and gas.

The origin of the kinetic theory

Until the formulation of this model, several events took place that provided the basis for this theory.

To begin with, the concept of the atom was born in Ancient GreeceThe atom, under the atomist school, whose disciples spread the idea that the atom is the indivisible unit that forms all matter in the universe. Democritus was one of its greatest exponents, but his proposals clashed directly with the ideas of Aristotle, which dominated the time, so they went unnoticed.

It was not until the beginning of the 19th century that the idea of the atom reappeared in the field of science, when John Dalton postulated the theory of the atom. John Dalton postulated the atomic theory, indicating that every substance is configured in the form of an atom.indicating that every substance is made up of atoms.

Prior to this, Daniel Bernoulli in 1738 argued that gases were formed by molecules that collide with each other and with surfaces, generating and with surfaces, generating the pressure that is felt. After the appearance of the atomic theory, it is now recognized that these molecules are made up of atoms.

The kinetic molecular theory arises from a set of studies that were carried out mainly in gases, and whose final conclusion was similar. Some of the outstanding works are those carried out by Ludwig Boltzmann and James Clerk Maxwell.

The argument

This kinetic molecular theory postulates that the matter is formed by a set of particles that are known as atoms or by molecules of these same ones, which are in constant motion. As they do not stop moving, sooner or later they collide with another atom or against a surface.

This collision is kinetic, in other words, energy is transferred without lossThe kinetic energy generated in the collision is translated into the pressure that is felt. The kinetic energy generated in the collision is translated into the pressure felt.

Difference between the states of matter

Although the kinetic molecular theory was born from the study of the gaseous state, since there were many studies on it that allowed the ideas to be drafted, it also serves to explain the constitution of liquids and solids. Moreover, it offers a way to see differences between the different states of matter.

The key point lies in the degree of motion of the atoms. Matter is made up of a set of particles that are in constant motion; in a gas, the atoms are free and move in a linear fashion throughout the available space, demonstrating the characteristic of gases to always occupy all the space available to them.

In the case of liquids, the distance between the atoms is not so great, but they are closer together.but they are closer together, although they continue to move at a slower speed. This explains why a liquid occupies a fixed volume, but can expand over a surface.

Finally, in the solid state the atoms are very close together, without free movement, although they vibrate on the spot. Therefore, solids occupy a specific space and do not vary in volume over time.

According to kinetic-molecular theory, the force that binds atoms together is known as the cohesive force. Its name is given because solids have a greater presence of these bonds, that is, it is more cohesive than a liquid or a gas.

The importance of this model

The interesting thing about this theory is how it relates the existence of the atom to measurable physical properties, such as pressure or temperature. pressure or temperature. In addition, it has a correlation with the mathematical formulas of the ideal gas laws.

I won't go into too much detail about this, but for example, it agrees with the formulas that indicate that at higher temperatures, atoms exhibit higher velocities. It is easy to understand, for ice to turn to liquid and then to vapor, heat must be applied. As the temperature rises, H2O molecules gain speed and break the cohesive forces, changing the state of matter.