Molecular structure has ... Which substance has a molecular structure

As is known, chemistry studies the structure and properties of substances, as well as their mutual transformations. An important place in the characterization of chemical compounds is the question of which particles they consist of. It can be atoms, ions or molecules. In solids they enter the nodes of the crystal lattices. The molecular structure has a relatively small number of compounds in a solid, liquid, and gaseous state.

In this article we will give examples of substances for which molecular crystal lattices are characteristic, and also consider several types of intermolecular interaction, characteristic for solids, liquids and gases.

Why you need to know the structure of chemical compounds

In each branch of human knowledge, it is possible to single out a group of fundamental laws on which further development of science is based. In chemistry is the theory of MV. Lomonosov and J. Dalton, explaining the atomic-molecular structure of matter. As scientists have established, knowing the internal structure, we can predict both the physical and chemical properties of the compound. All a huge number of artificially synthesized organic substances (plastics, drugs, pesticides, etc.) have predetermined characteristics and properties, the most valuable for its industrial and household needs.

Knowledge of the features of the structure and properties of compounds are in demand when carrying out control sections, tests and examinations in the course of chemistry. For example, in the proposed list of substances to find the right answers: what substance has a molecular structure?

• Zinc.
• Magnesium oxide.
• Diamond.
• Naphthalene.

The correct answer is: zinc has a molecular structure, as well as naphthalene.

Intermolecular Interaction Forces

It has been experimentally established that the molecular structure is characteristic for substances with low melting points and low hardness. How can we explain the fragility of the crystal lattices of these compounds? As it turned out, everything depends on the strength of the joint influence of particles in their nodes. It has an electrical nature and is called intermolecular interaction or van der Waals forces, which are based on the influence of oppositely charged dipole molecules on each other. It turned out that there are several mechanisms of their formation, depending on the nature of the substance itself.

Acids as compounds of molecular composition

Solutions of most acids, both organic and inorganic, contain polar particles that are oriented with respect to each other by oppositely charged poles. For example, in a solution of chloride acid HCI there are dipoles, between which there are orientational interactions. As the temperature of the molecules of hydrochloric, hydrobromic (HBr) and other halogen-containing acids increases, the orientation effect decreases, since the thermal motion of the particles interferes with their mutual attraction. In addition to the above listed substances, the molecular structure has sucrose, naphthalene, ethanol and other organic compounds.

How do induced charged particles arise

Earlier we considered one of the mechanisms of Van der Waals forces acting, called orientation interaction. In addition to organic substances and halogen-containing acids, the molecular structure has hydrogen oxide-water. In substances consisting of nonpolar, but prone to the formation of dipoles, molecules, such as CO ₂ carbon dioxide, it is possible to observe the appearance of induced charged particles - dipoles. Their most important property is the ability to be attracted to each other, thanks to the appearance of forces of electrostatic attraction.

Molecular structure of gas

In the previous subheading, we mentioned a compound such as carbon dioxide. Each of its atoms creates around itself an electric field that polarizes the atom to a nearby carbon molecule. It is modified into a dipole, which, in turn, becomes capable of polarizing other CO ₂ particles. As a result, the molecules are attracted to each other. The inductive interaction can also be observed in substances consisting of polar particles, although in this case it is much weaker than the orientational van der Waals forces.

Dispersion interaction

Both the atoms themselves and the particles in their composition (nuclei, electrons) are capable of continuous rotational and vibrational motion. It leads to the appearance of dipoles. According to the research of quantum mechanics, the emergence of instant double-charged particles occurs both in solids and in liquids synchronously, in such a way that the ends of molecules located side by side turn out to be opposite poles. This leads to their electrostatic attraction, called the dispersion interaction. It is characteristic of all substances, except those that are in the gaseous state, and whose molecules are monatomic. However, van der Waals forces can arise, for example, in the transition of inert gases (helium, neon) to the liquid phase at low temperatures. Thus, the molecular structure of bodies or liquids determines their ability to form various types of intermolecular interaction: orientational, induced or dispersive.

What is sublimation?

Molecular structure of a solid body, for example, iodine crystals, causes such an interesting physical phenomenon as sublimation - volatilization of I ₂ molecules in the form of violet vapor. It occurs from the surface of a substance in the solid phase, bypassing the liquid state.

This visually effective experience is often carried out in school chemistry classrooms to illustrate the structural features of molecular crystal lattices and the related properties of compounds. Usually it is low hardness, low melting and boiling points, poor heat and electrical conductivity, volatility.

Practical use of knowledge about the structure of substances

As we have seen, a certain correlation can be established between the type of crystal lattice, the structure and the properties of the compound. Therefore, if the characteristics of the substance are known, it is easy enough to predict the features of its structure and composition of particles: atoms, molecules or ions. The information obtained can also be useful if, in chemistry assignments, it is necessary to select from a definite group of compounds the substances having a molecular structure, eliminating those with atomic or ion types of lattices.

Summing up, we can draw the following conclusion: the molecular structure has a solid body, and its spatial structure of crystal lattices, and the peculiarities of the arrangement of polarized particles in liquids and gases are completely responsible for its physical and chemical properties. Theoretically, the properties of compounds containing dipoles depend on the magnitude of the intermolecular interaction forces. The higher the polarity of the molecules and the smaller the radius of the atoms in their composition, the stronger the orientational forces arising between them. Conversely, the more atoms that make up a molecule, the higher its dipole moment, and, hence, the more significant the dispersion forces. Thus, the molecular structure of a solid body also affects the interaction forces between its particles - dipoles.