Molecular kinetic theory: the 3 states of matter
It is said that the whole universe is formed of matter and that when it changes, energy is generated. And as is normal, the curious nature of the human being has led us to ask ourselves on many occasions that all this matter is formed. Throughout history, different models have been devised to explain this, being one of them the molecular kinetic theory .
According to this model, matter would be constituted by a fundamental unit that can not be appreciated with the senses, I am talking about the atom. In turn, the atoms are grouped 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 .
- Maybe you're interested: "The 5 types of chemical bonds: this is how matter is composed
The origin of the kinetic theory
Up to the formulation of this model, different events occurred that allowed the bases to be offered to offer this theory.
To get started, the concept of atom was born in ancient Greece , under the atomistic school, whose disciples spread the idea that the atom is the indivisible unit that forms all matter of the universe. Democritus was one of its greatest exponents, but its proposals clashed directly with the ideas of Aristotle, which dominated the era, so they went unnoticed.
It was not until the beginning of the 19th century when the idea of the atom reappeared in the field of science, when John Dalton postulated the atomic theory , indicating that every substance is configured by atoms.
Prior to that, Daniel Bernoulli in 1738 argued that the gases were made up of molecules that collide with each other and with the surfaces, generating the pressure that is felt. After the appearance of the atomic theory, it is now recognized that these molecules are configured by atoms.
The molecular kinetic theory comes 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 made by Ludwig Boltzmann and James Clerk Maxwell.
- Related article: "The 9 postulates of Dalton's atomic theory"
The argument
This molecular kinetic theory postulates that matter is formed by a set of particles that are known as atoms or by molecules of these, that are constantly moving . As they do not stop moving, sooner or later they collide with another atom or against a surface.
This collision is performed kinetically, in other words, energy is transferred without losses , so that the colliding atom is fired in the other direction at the same speed, without stopping the movement. The kinetic energy that is generated in the collision is translated into the pressure that is felt.
Difference between the states of matter
Although the molecular kinetic theory was born from the study of the gaseous state, since there were many studies on it that allowed to write the ideas, 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 movement of atoms . Matter is formed by a set of particles that are in constant motion; in a gas, the atoms are free and move linearly throughout the available space, demonstrating the characteristic of gases always occupy all the space they have.
In the case of liquids, the distance between the atoms is not so big , but they are more together, although they continue moving with less speed. This explains why a liquid occupies a fixed volume, but can expand on a surface.
By last, in the solid state the atoms are very close, without a free movement although they vibrate in the place. Therefore, solids occupy a specific space and do not vary in volume.
According to molecular kinetic theory, the force that binds atoms together is known as Cohesion force . Its name is given because the solids that have more presence these unions, that is, 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 with measurable physical properties, such as the pressure or the temperature . In addition, it has a correlation with the mathematical formulas of the laws of ideal gases.
I will not go into much detail about this, but for example, it agrees with the formulas that indicate that at higher temperatures, atoms have a higher speed. It is easy to understand, for an ice to pass to liquid and then to steam it is necessary to apply heat. When the temperature rises, the H2O molecules gain speed and break the cohesion forces, changing the state of the matter.
