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What are intermolecular forces?

Intermolecular forces

In the field of chemistry, biology and physics, there is a group of intermolecular forces that act on groups of molecules considered stable or on some functional groups that contain large molecules or macromolecules. This type of force is also known as the Van de Waals force . They are forces that despite being weak can generate a large number of phenomena and provide an explanation about why some molecules that are light are liquid or solid at a certain temperature and pressure , generally normal.

Intermolecular forces What are they, characteristics, types, properties, examples 

What are intermolecular forces?

Intermolecular forces are all those interactions whose main function is to be able to hold molecules together , they are a type of electrostatic force that provides a series of properties to liquids and solids.

  • Definition
  • Characteristics of intermolecular forces
  • Types of intermolecular forces
  • Properties
  • How they differ from intramolecular forces
  • Importance
  • Examples of intermolecular forces

Definition

It is important to remember that there are atoms inside a molecule and that they remain united. This union occurs thanks to intermolecular forces , which can be essentially ionic or covalent bonds . This type of force is what is responsible for holding all the molecules together and also, they are responsible for providing a series of characteristics with respect to the chemical part of the substances.

Characteristics of intermolecular forces

The main characteristics that can be observed in intermolecular forces are the following:

  • They do not have the same strength as intramolecular ones .
  • It has the ability to be able to exert an attraction between the molecules that are part of a certain substance.
  • Its intensity tends to decrease drastically when the distance between the molecules is increased.
  • This type of force does not have any kind of advantage in gases .
  • It can be seen reflected in the different properties that liquids have, such as the melting point and the boiling point .
  • They have an order of magnitude which is relative and is based on the hydrogen bond, the dipole-dipole and the London scattering.
  • It occurs in the presence or absence of electrons .
  • The different intermolecular forces that can act between the molecules can be classified into permanent , induced , dispersed dipoles and finally, hydrogen bonds.

Types of intermolecular forces

There are several types of intermolecular forces which are mentioned below.

Van der Waals force

This type of force is located in the group of produces stabilization of the molecules forming a non-covalent chemical bond in which two types of forces participate, one is dispersion or attraction and the other, repulsion . The dispersion force is electrostatic because atoms have the ability to form small dipoles that, when electrons rotate around the nucleus, the dipole causes the atoms to polarize creating small attractive forces between the dipoles.

Electrostatic repulsion occurs in the electronic shells of the atoms that are located next to each other and the result is a minimum distance between the two nuclei. It is worth mentioning that the energy of the Van der Waals bond is 1 – 2 kcal / mol. Finally, the Van der Waals bond has three types or classes of bond, those of orientation, those of induction and those of dispersion.

Ion-dipole forces

This type of intermolecular force occurs when the ions that exist in a certain substance can interact with the dipoles that exist in a polar covalent molecule . In the polar bond, the atom that presents a higher electronegativity has the ability to attract electrons and in this way produces a negative dipole around it while at the same time a positive dipole is formed in the place where there is less amount of electronegativity.

In ion-dipole forces, the cation has a type of electrostatic attraction and is attracted by the negative dipole, the anion for its part is attracted by the electrostatic force towards the positive dipole.

Maxwell forces

This type of force refers to the different electric and magnetic fields that exist in time and that influence electromagnetic waves. There are four different forces, gravity , electromagnetism , strong and weak nuclear interaction .

Properties

The properties of the intermolecular forces will depend on the effect they produce on the physical and chemical properties of the elements. That said, there are properties related to state of aggregation , melting and boiling point , solubility , molecule density , and viscosity .

How they differ from intramolecular forces

Intramolecular forces are those that unite the atoms within a molecule and are forces that, in order to be executed, require the presence of a chemical change to later determine the chemical properties found in a certain substance. On the other hand, the intermolecular forces act on the molecules causing them to repel or attract each other , they are then in charge of determining the different physical properties of the elements.

Importance

This type of force is important mainly in gases as they are responsible for how they can behave. They also have a fundamental role in the states of aggregation of matter, with this we refer to the liquid, solid or gaseous states. These bonds actively participate in a series of processes in living species and in biological systems, such as enzymatic catalysis .

Without this type of force, life could practically not exist since they are in charge of giving the properties to substances , for example, if water did not have bonds through intermolecular forces, it would change state very easily and could not develop no life on earth. They are forces that are present in alcohol, DNA, carbohydrates, proteins, glucose and cellulose, without them, all these substances and many more could not exist.

Examples of intermolecular forces

Ammonia

Ammonia has two types of intermolecular forces, London’s and the interaction between dipoles . This happens because in this element there is a free electric cloud and for this reason, the dipoles are different from zero.

Ethanol

Ethanol is a highly volatile liquid and uses dipole-dipole forces to control its molecular weight. It has a large number of hydrogen bonds and thanks to the intermolecular force, this substance has a fairly high boiling point.

Water

Water has intense intermolecular forces and are known as hydrogen bonds , they act through a dipole-dipole force that occurs between the hydrogen atom and the electronegative atom. It also has small elements as well as a great electronegativity which causes partial charges to occur.

Methane

Methane has London intermolecular and permanent dipole forces as it has nonpolar molecules.

Ethyl alcohol

This substance also has hydrogen bonds , considered as the main intermolecular forces and for this reason, this type of alcohol has a high boiling point . Also, it is quite polarized due to hydrogen and oxygen bonds.

Diamond

The structure of diamonds depends on intermolecular forces which are based on the formation of hydrogen bonds .

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