“Atoms, molecules and ions. Theme

Every day we use some objects: we take them in our hands, perform any manipulations on them - turn them over, examine them, in the end, break them. Have you ever thought about what these items are made of? "What is there to think about? Of metal / wood / plastic / fabric!" - many of us will answer in bewilderment. This is partly the correct answer. And what are these materials made of - metal, wood, plastic, fabric and many other substances? Today we will discuss this issue.

Molecule and atom: definition

For a knowledgeable person, the answer to it is simple and banal: from atoms and molecules. But some people get puzzled and start bombarding them with questions: "What is an atom and a molecule? What do they look like?" etc. We will answer these questions in order. Well, first of all, what are an atom and a molecule? Let us tell you right away that these definitions are not the same thing. And even more than that, these are completely different terms. So, an atom is the smallest part of a chemical element, which is the carrier of its properties, a particle of matter of scanty mass and size. And a molecule is an electrically neutral particle, which is formed by several connected atoms.

What is an atom: structure

An atom consists of an electron shell and (photo). In turn, the nucleus consists of protons and neutrons, and the shell consists of electrons. In an atom, protons are positively charged, electrons are negatively charged, and neutrons are not charged at all. If the number of protons corresponds, then the atom is electrically neutral, i.e. if we touch a substance formed from molecules with such atoms, then we will not feel the slightest electrical impulse. And even super-powerful computers will not catch it due to the absence of the latter. But it happens that there are more protons than electrons, and vice versa. Then it would be more correct to call such atoms ions. If there are more protons in it, then it is electrically positive, but if electrons predominate, it is electrically negative. Each particular atom has a strict number of protons, neutrons and electrons. And it can be calculated. The template for solving problems of finding the number of these particles looks like this:

Chem. element - R (insert element name)
Protons (p) -?
Electrons (e) -?
Neutrons (n) -?
Solution:
p = serial number of chem. element R in the periodic system named after D.I. Mendeleev
e = p
n = А r (R) - № R

What is a molecule: structure

A molecule is the smallest particle of a chemical, that is, it is already directly included in its composition. A molecule of a certain substance consists of several identical or different atoms. The structural features of molecules depend on physical properties the substance in which they are present. Molecules are made up of electrons and atoms. The location of the latter can be found using structural formula... allows you to determine the course of a chemical reaction. They are usually neutral (have no electrical charge) and have no unpaired electrons (all valences are saturated). However, they can be charged, then their correct name- ions. Also, molecules can have unpaired electrons and unsaturated valences - in this case, they are called radicals.

Conclusion

Now you know what an atom is and all substances, without exception, consist of molecules, and the latter, in turn, are built of atoms. The physical properties of a substance determine the arrangement and connection of atoms and molecules in it.

Chemistry is the science of matter.

Elementary particle is an indivisible micro-object on the scale of atomic nuclei, which is indivisible.

Subatomic particle is an elementary or constituent particle that is part of the atom. Subatomic particles include an electron, a proton, and a neutron.

Neutron- elementary particle, has no charge. Almost equal in mass to a proton.

Proton - elementary particle, carrier of a positive charge. Almost equal in mass to the neutron.

Electron- an elementary particle, a carrier of a negative charge. The mass of an electron is approximately equal to 1/1836 of the mass of a proton.

Nucleons is a common name for protons and neutrons.

Atom- a unit of matter, consisting of a positively charged nucleus, which is surrounded by the same number of negatively charged electrons. The atom is electrically neutral.

Core- the central part of the atom, consisting of positively charged protons and neutral neutrons; the mass of each of these particles is approximately equal to 1 amu.

Atomic mass unit (amu)- unit of mass used for the masses of molecules, atoms, atomic nuclei and elementary particles. The atomic mass unit is defined as 1⁄12 of the mass of a 12 C carbon atom.

Atomic (ordinal) number - the total number of protons in the nucleus of an atom. It also shows the number of electrons in an atom.

Mass number is the total number of nucleons in an atom.

Atomic mass- mass number, expressed in atomic mass units. The atomic mass is always slightly less than the sum of the masses of the particles that make up the atom, since when an atom is formed from these particles, part of the mass is converted into energy and released in the form of radiation (mass defect).

Mass defect- the difference between the total mass of all nucleons of the nucleus in a free state and the mass of the nucleus.

Communication energy is the energy required to split the nucleus into free nucleons.

Isotope- atoms of the same chemical element with a different number of neutrons in the nucleus. Each isotope of an element has its own atomic mass, and the serial number and symbol of the element remain unchanged.

Molecule- a set of atoms held together by chemical bonds.

Chemical bond- This is the interaction of atoms, which determines the stability of the molecule (or crystal) as a whole.

Electronegativity- the ability of an atom to attract electrons.

Electronic pair- the bound state of two interacting electrons.

Covalent non-polar connection - a kind of covalent chemical bond, which is formed by When atoms interact with the same electronegativity. An electron pair is formed between them, which is equally owned by both atoms.

Covalent polar bond -a kind of covalent chemical bondwhich is formed by n when the interaction of atoms, the value of electronegativity is different, but not sharply; there is a displacement of the common electron pair to a more electronegative atom.

Ionic bond - the bond that is formed in the interaction of atoms that differ sharply from each other in electronegativity.

Hydrogen bond- a bond that forms between the hydrogen atoms of one molecule and the atom of a strongly electronegative element (O, N, F) of another molecule.

Molecular mass- sum atomic masses of all atoms in a molecule.

Intermolecular interactions- interaction of molecules with each other, which does not lead to rupture or the formation of new chemical bonds... Intermolecular interactions include all the forces of intermolecular attraction and repulsion.

Vanderwaals forces- a kind of forces of intermolecular interaction, due to which a substance has three states of aggregation.

Polar molecule- a molecule formed by atoms using a covalent polar chemical bond.

Avogadro's number- the number of particles in 12 grams 12 C and equal to 6.02 · 1023.

1 Mole is the amount of substance, equal to the number Avogadro, i.e. 6.02 · 10 23 particles.

Molar mass- the mass of one mole of a substance, measured in g / mol.

And he- A non-elementary particle that has a charge due to the removal or acquisition of one or more electrons.

Cation is a positively charged ion.

Anion- negatively charged ion.

Oxidation state- this is the number of electrons that must be added (reduced) or subtracted (oxidized) to the ion so that it turns back into a neutral atom.

Oxidation- withdrawal or complete removal of electrons from a particle.

Recovery- attachment or approach of electrons to a particle.

Complex ion is a complex ion consisting of two or more simple ions.

Salt is a compound of a certain number of cations and anions, which has a net charge of zero.

Salt crystal- stable formation of cations and anions, in which an ion of each type is as far away as possible from other ions with a charge of the same sign.

Coordination number - the number of atoms or chemical groups directly attached to the central atom in the complex ion or a molecule.

Solvation- electrostatic interaction between particles (ions, molecules) of a solute and a solvent. In simple words, it's just a dissolution process.

Hydration is a process of solvation in water.

Cathode- a negative electrode that supplies electrons.

Anode- a positive electrode that picks up electrons.

Electrolysis is a method of separating the components of a compound using electric current passing through a molten compound or solution.

1 Faraday- a value equal to 96485 C is simply the charge of 1 mole of electrons.

According to modern concepts:

Atom Is an electrically neutral particle consisting of a positively charged nucleus and negatively charged electrons.

It is wrong to say that "an atom is the smallest particle of a chemical element that retains all its chemical properties", because. chemical element - this is a kind of particles (atoms, ions, nuclei) with a certain charge of the nucleus; therefore the element does not consist of atoms!

In addition, chemical properties are the energy and speed of a chemical reaction, and they depend not only on the composition of the reacting particle, but also on its energy state, geometric shape and so on. Therefore, chemical properties are not possessed by atoms (and molecules), but their aggregates - chemical substances.

Molecule Is the smallest electrically neutral set of atoms that form a certain structure through chemical bonds, which determines the composition of a substance.

According to modern concepts, substances in a gaseous and vapor state consist of molecules. In the solid state, only substances are made of molecules, the crystal lattice of which has molecular structure(most organic substances; non-metals, except for boron, silicon, allotropic modifications of carbon; carbon dioxide CO 2; water H 2 O).

Most of the solid inorganic substances does not have a molecular structure: their lattice does not consist of molecules, but of other particles (ions, atoms); they exist in the form of macro-bodies (NaCl crystal, quartz druse, a piece of iron, etc.). Non-molecular substances include salts, metal oxides, diamond, silicon, metals, etc.

The chemical bond between molecules in substances with a molecular structure is less strong than between atoms in a molecule, therefore, their melting and boiling points are relatively low. In substances with a non-molecular structure, the chemical bond between particles is very strong, so their melting and boiling points are high.

1.3.2. The masses of atoms and molecules. Moth

The masses of atoms and molecules are extremely small, so a special unit of measurement is used for them - atomic mass unit (abbreviated designation "a. e. m."):

1 a. unit m = 1.66 · 10 –27 kg.

For example, the absolute mass of an aluminum atom:

m o (Al) = 4.482 · 10 –26 kg = 27 amu. eat.

More often use dimensionless magnitudes- relative atomic and molecular weights.

Relative atomic mass A r - a number showing how many times the mass of a given atom is more than 1/12 of the mass of a carbon atom 12 C.

For example:

A r (Al) = = 27.

Relative molecular weight M r - a number showing how many times the mass of a given molecule is more than 1/12 of the mass of a carbon atom 12 C.

For example:

M r (SO 2) =
= 64.

Along with the units of mass and volume, in chemistry they also use a unit of the amount of a substance called a mole (abbreviated designation - "mole").

Moth Is the amount of a substance containing the same number of structural units (atoms, molecules, ions, nuclei, electrons, radicals) as there are atoms in 0.012 kg (12 g) of carbon 12 C.

One mole of any substance contains Avogadro's number structural units, namely

N A = 6.02 · 10 23 mol –1.

A mole of a substance has a certain mass (molar mass) and a certain volume (molar volume).

Molar (molar) mass M Is the mass of 1 mol of a substance, expressed in mass units:

M (Al) = 27 g / mol; M (H 2 SO 4) = 98 g / mol.

Molar (molar) volume V m - the volume of 1 mol of a substance, expressed in units of volume:

V m (CO 2) = 22.4 L / mol (n.a.) 1; V m (H 2 O) = 18 ml / mol.

Example 1.1 ... During the Vietnam War (1962–1971), American troops used defoliants extensively to combat guerrillas. The "agent orange" defoliant (orange reagent) causes an accelerated fall of the leaves of trees. In total, 57 thousand tons of this preparation was sprayed over the jungle, which contained up to 170 kg of dioxin as an impurity. Now this defoliant is known under the name 2,4-D (2,4-dichlorophenoacetic acid). Calculate the mass of one defoliant molecule (molecular formula C 8 H 6 O 3 Cl 2): ​​a) in grams; b) in atomic mass units.

Solution:

a). To calculate the mass of a 2,4-dichlorophenoacetic acid molecule, you need to know its molar mass:

M (C 8 H 6 O 3 Cl 2) = 8 12 + 6 1 + 3 16 + 2 35.5 = 221 (g / mol).

We calculate the amount of substance according to the following formulas:

ν = m / M; ν = N / N A,

where m is the mass, M is the molar mass, N is the number of atoms or molecules, N A = 6.02 · 10 23 mol –1 is Avogadro's constant.

By combining these formulas, you can express the mass in terms of the number of molecules:

m = ν M = .

Substituting into the resulting formula N = 1, M = 221 g / mol, N A, we find:

m (C 8 H 6 O 3 Cl 2) =
= 36.7 · 10 –23 (g).

b). The absolute mass of a molecule is equal to the relative molecular weight multiplied by 1 amu. eat.

m (C 8 H 6 O 3 Cl 2) = 1 a. e.m.M r (C 8 H 6 O 3 Cl 2)

The relative molecular weight is numerically equal to the molar weight:

M r (C 8 H 6 O 3 Cl 2) = 221;

m (C 8 H 6 O 3 Cl 2) = 1 a. units 221 = 221 units eat.

Example 1.2. How many molecules are there in 1 liter of water?

Solution. 1. Weight 1 l water can be calculated using the density value (the density of water at 4С is equal to 1 g / cm 3):

m (H 2 O) = V (H 2 O) ρ (H 2 O);

V (H 2 O) = 1 l = 1 dm 3 = 1000 cm 3;

m (H 2 O) = 1000 cm 3 1 g / cm 3 = 1000 g.

2. Further reasoning can be carried out in two ways.

Method 1: by the amount of substance.

Using the formulas ν = m / M and ν = N / N A, we find:

ν (H 2 O) = m (H 2 O) / M (H 2 O); ν (H 2 O) = 1000 g / 18 g / mol = 55.6 mol.

N (H 2 O) = ν (H 2 O) N A; N (H 2 O) = 55.6 mol · 6.02 · 10 23 mol –1 = 334.7 · 10 23 = 3.35 · 10 25.

Method 2: using proportions.

18 g (1 mol) of H 2 O contain 6.02 · 10 23 molecules;

1000 g of H 2 O contain N molecules.

N (H 2 O) = 1000 6.02 10 23/18 = 3.35 10 25.

Example 1.3. Calculate the molar volume of aluminum if its density is 2.7 g / cm 3.

Solution. To calculate the molar volume through the density of a substance, you need to know its molar mass:

ρ (Al) =
; V m (Al) =
.

V m (Al) =
= 10 cm 3 / mol = 0.01 L / mol.

Lesson objectives: to deepen students' knowledge about atoms and molecules as complex structural particles of matter; give the concept of ions as charged particles; based on the structure of the atom, give the concept of a chemical element as a certain type of atoms; to acquaint students with modern Ukrainian nomenclature; to give an idea of ​​the distribution of chemical elements in nature.

Lesson type: combined.

Forms of work: heuristic conversation, story, work with a reference scheme.

Equipment: periodic table of chemical elements.

II. Homework check

1. We deafen the method of separating the mixture: salt + alcohol + water + iron filings.

Decantation and filtration.

Distillation.

Evaporation and crystallization.

2. Several students to choose from offer their mixture. We listen to the separation method, discuss the proposed option.

III. Updating basic knowledge

Recall from the courses in natural history and physics the main stages in the development of the theory of the structure of the atom.

Heuristic conversation

1. The theory of atoms of Democritus.

2. Creation of atomic-molecular doctrine by MV Lomonosov and J. Dalton.

3. Nuclear model of the atomic structure of E. Rutherford:

Atoms are composed of a positively charged nucleus and an electron shell.

The charge of the atomic nucleus and the total charge of all electrons are the same. The atom is electrically neutral.

Electrons move around the nucleus with different energy reserves, at different distances from the nucleus and form energy levels.

Consider the diagram of the structure of the atom.

The nucleus is made up of protons and neutrons.

The charge of the nucleus is equal to the ordinal number of the element in the periodic system (we fill in the diagram).

So let's summarize.

An atom is the smallest electrically neutral particle of matter, consisting of a positively charged nucleus and negatively charged electrons.

What happens if the number of protons and electrons in an atom is different?

He will enter the charge, and if

np< ne - , то отрицательного;

np> ne, then positive.

The charged particles are called ions. Positive ions are cations and negative ions are anions.

For example: H + - positive Hydrogen ion (Hydrogen cation);

F - - negative ion Fluorine (anion of Fluorine).

Let's draw a diagram of the structure of atoms and ions of Hydrogen and Fluorine.

We will fill the empty seats ourselves:

IV. Learning new material

The kind of atoms with the same nuclear charge is called a chemical element.

Consider the periodic table of chemical elements. In it, with the help of chemical symbols, all chemical elements known to man are depicted.

Chemical symbols in this form were proposed by the Swedish chemist J. J. Berzelius. They represent the first letter of the Latin name for chemical elements. If the names of several elements begin with the same letter, then another letter is added to the chemical symbol. These designations for chemical elements are international and understood by chemists and other scientists around the world.

In addition to the chemical symbol, the elements have their own names. Let's get acquainted with some of them according to the modern Ukrainian nomenclature. (For a textbook or diagram, we get acquainted with the names, chemical symbols of the elements and the pronunciation of the names of the 20 elements.)

In nature, chemical elements are distributed unevenly. Consider a diagram of their distribution in the Universe.

V. Securing new material

1. Let's construct a diagram of the structure of the atom of lithium using the periodic system.

The ordinal number is 3, therefore, the charge of the nucleus is Li +3, the number of electrons is 3. The scheme can be depicted as follows:

Scheme Be yourself.

The serial number is 4.

Core charge - +4.

The number of electrons is 4.

2. Find in the periodic system the designations of the following chemical elements:

Ferrum - Fe; Aurum - Au; Sulfur - S; Carbon - C.

3. Using the periodic system, fill in the missing cells in the table.

Vi. Lesson summary

Today we have not only repeated information about the structure of the atom, but also learned a lot of new things.

In particular:

A chemical element is a kind of atoms with the same nuclear charge;

Ion is a charged particle;

We learned the names of chemical elements;

We got acquainted with the periodic system of chemical elements of DI Mendeleev.

Creative task. Draw up a diagram of the structure of atoms B, C, Al.

TOPIC 1: Structure of materials

PART 1. “Materials Science. Structural technology

materials "

The concept of structure …………………………. ………………………

Atom, molecule, chemical bond ……………………………….

Phase state of matter …………………………………… ..

Gas and liquid …………………………………………………… ..

Solid …………………………………………….… ..

The technical significance of materials depends on the structure and is expressed in their properties. The structure of materials characterizes their structure.

Structure–The set of stable bonds of the material, ensuring its integrity and preservation of the basic properties during external and internal changes.

The structure of materials is determined by many factors: the structure of atoms, ions, molecules, the distribution of electrons in them, the type of bonds between particles, etc. In materials science, it is customary to consider three levels of the structure of materials: atom-molecule-phase.

Any substance is not something continuous, but consists of separate very small particles. The differences between substances are due to the difference between their particles: the particles of one substance are the same, the particles of different substances are different. Under all conditions, the particles of matter are in motion, and the higher the body temperature, the more intense this movement.

For most substances, particles are molecules. Molecules, in turn, are made up of atoms.

Molecule- the smallest particle of a substance that has its chemical properties.

Atom- the smallest particle of a chemical element that has its chemical properties.

An atom is a system consisting of a positively charged nucleus around which negatively charged electrons revolve. Electrons are attracted to the nucleus and repelled from each other. The electrons located closer to the nucleus are subject to greater attraction; they weaken the attraction of external electrons, which are at a greater distance from the nucleus. External electrons can detach from one atom and attach to another atom, changing the number of its external electrons. Such electrons are called valence.

The molecule may include different number atoms. In this case, the atoms can combine with each other not only in different ratios, but also in different ways. Therefore, with a relatively small number of chemical elements, the number of different substances is very large.

An atom, having entered into interaction with the atoms of another simple substance, violates its stable structure and loses the chemical properties of the original simple substance. It forms with other atoms a molecule of a new chemical substance with a new complex of chemical and physical properties. Molecules of complex substances are composed of various atoms that have entered into chemical interaction, for example, where the superscripts indicate the group number Periodic table elements, and the lower ones are the number of atoms of this element in the compound. Molecules of simple substances consist of identical atoms that also interact with each other.

To such simple substances include inert gases and metals.

In substances with an ionic or atomic structure, the carrier chemical properties is not a molecule, but those combinations of ions and atoms that form a given substance.

An atom is a complex system of negatively charged electrons and a positively charged nucleus. Due to the interaction of electric fields created by electrons and the nuclei of atoms involved in the formation of a molecule or crystal, chemical bond, which can be covalent, ionic, metallic, molecular. The forces of attraction arise due to the interaction of electrons with posit. charge the nucleus of its own atom, as well as with posit. charge nuclei of the neighboring atoms. Repulsive forces are formed as a result of the interaction will put the contamination of the nuclei of neighboring atoms when they approach. They appear with a strong approach and grow more intensively than the forces of attraction.

F

Repulsion

Resultant strength

Attraction d0

Rice. Change in the force of interaction (a) and binding energy (b) when atoms approach each other in a crystal

The balancing of forces occurs when particles approach at a distance d0. This approach corresponds to the minimum binding energy Eb, which makes the crystal thermodynamically stable The binding energy for various crystals is given in the table

It determines the melting point, elastic modulus, temperature coefficient of linear expansion, etc.

Covalent chemical bond is formed by two electrons, and this electron pair belongs to two atoms. Crystals dominated by forged. The type of bond is called covalent. They are formed by elements of the IV, V, VI subgroups B Period.table.Mendel.: Carbon, silicon, germanium, antimony, bismuth, etc. When interacting, atoms socialize their valence electrons with neighboring atoms, thus completing the valence zone. Each bond is formed by a pair of electrons moving in closed orbits between two atoms. The number of atoms n, with which the generalization of electrons occurs, depends on the valence of the element and is determined by the form.

where N is the valence of the elements.

For example, for carbon this number is n = 4, i.e. a carbon atom has four valence electrons, through which it forms four directional bonds and enters into exchange interaction with four neighboring atoms.

The formation of a chemical bond between atoms is the result of the interpenetration ("overlapping") of electron clouds, which occurs when interacting atoms approach each other. Due to this interpenetration, the density of the negative electric charge in the internuclear space increases. Positively charged atomic nuclei are attracted to the overlapping region of electron clouds, which leads to the formation of a stable molecule.

The covalent bond is the stronger than in to a greater extent overlapping interacting electronic clouds.

If a diatomic molecule consists of atoms of one element (for example, a molecule, etc.), then each electron cloud formed by a common pair of electrons and carrying out a covalent bond is distributed in space symmetrically relative to both atoms. In this case, the covalent bond is called non-polar. If a diatomic molecule consists of atoms various elements, then the common electron cloud is displaced towards one of the atoms, so that there is an asymmetry in the charge distribution. In such cases, the covalent bond is called polar.

For example, in the HCl molecule, the total electron pair is displaced towards the chlorine atom. Therefore, the hydrogen chloride molecule is a polar molecule.

The polarity of molecules has a noticeable effect on the properties of the substances they form. Substances formed by polar molecules have, as a rule, more high temperatures melting and boiling than substances made from non-polar molecules.

Ionic bond- is carried out as a result of mutual electrostatic attraction of oppositely charged ions.

During chemical reactions atoms attach electrons to atoms of other elements or donate electrons to other atoms.

Atoms that donated some of the electrons acquire a positive charge and become positively charged ions... Atoms that have attached electrons turn into negatively charged ions. Oppositely charged ions are held together by the forces of electrostatic attraction.

Two opposite ions, attracted to each other, retain the ability to electrostatically interact with other ions. This ion can coordinate around itself a certain number of ions of the opposite sign. Ionic molecules are capable of bonding with each other.

Substances with ionic bonds in the molecule are characterized by high melting and boiling points.

Metal bond Is a bond in which the electrons of each individual atom belong to all the atoms in contact. In this case, valence electrons are able to move freely in the volume of the crystal. The metallic bond is characteristic of metals, their alloys and intermetallic compounds.

The metallic state arises in a complex of atoms when, when they approach each other, the outer electrons lose their bond with individual atoms, become common, i.e. collectivized and freely move between positively charged and periodically located ions.

The stability of a metal, which is thus an ion-electron system, is determined by the electric attraction between positively charged ions and generalized electrons.

The strength of the bond in metals is determined by the forces of repulsion and the forces of attraction between ions and electrons and does not have a pronounced directional character. The atoms in the metal are arranged regularly, forming a regular crystal lattice, which corresponds to the minimum interaction energy of atoms.

The metallic bond is non-directional. The consequence of this is a high coordination number and a large compactness of the crystal structures of metals.

Among metal crystals, the phenomenon is common polymorphism- the ability in a solid state at different temperatures (or pressures) to have Various types crystal structures. These crystal structures are called allotropic forms, or modifications. The low-temperature modification is denoted by a, and the high-temperature modification - b, g, d, etc.

The specific properties of the metallic bond explain the characteristic properties of metals. The high electrical conductivity of metals is explained by the presence of free electrons in them. Which move in the potential field of the grid. As the temperature rises, the vibrations of atoms (ions) intensify, which impedes the movement of electrons, as a result of which the electrical resistance increases. At low temperatures the vibrational motion of ions (atoms) is greatly reduced and the electrical conductivity increases.

The high plasticity of metals is explained by the periodicity of their atomic structure and the lack of directionality of the metal bond. Under mechanical action on a solid, its individual layers crystal lattice move relative to each other. In crystals with an atomic structure, this leads to rupture covalent bonds with atoms belonging to different layers, and the crystal is destroyed. In crystals with an ionic structure, with the mutual displacement of the layers, a position is inevitably created in which like charged ions are next to each other, while electrostatic repulsion forces arise and the crystal is destroyed. In the case of a metal, when individual layers of its crystal lattice are displaced, only a certain redistribution of the electron gas occurs, which binds the metal atoms to each other, but the breaking of chemical bonds does not occur — the metal is deformed without being destroyed.

Molecular bond- the weakest bond (van der Waals bond) exists between molecules in some substances with a covalent intramolecular bond. The attraction between molecules here is provided by the coordinated movement of electrons in neighboring molecules: at any moment of time, the electrons are as far away from each other as possible and are as close as possible to (+) ions. In this case, the force of attraction of electrons with (+) ions is higher than the force of repulsion between the electrons of the outer orbits.