Bonds arise between atoms in a water molecule. The connection of water molecules to each other

The structure hydrogen bond we will analyze with you an example interactions water molecules among themselves.

The water molecule is dipole... This is because the atom hydrogen associated with more electronegative element oxygen having experienced flaw electrons and therefore capable to interact with an oxygen atom of another water molecule.

As a result interactions arises hydrogen bond (Rice. 2.1):

2.1. The mechanism of formation of hydrogen bonds between water molecules

This is explained by hydrogen atom associated with more electronegative element having unshared electron pair(nitrogen, oxygen, fluorine, etc.), experiences flaw electrons and therefore is able to interact with unshared a pair of electrons another electronegative atom this or another molecules.

This also results in hydrogenconnection, which is graphically denoted three points(Rice.):

Rice. 2.2. The mechanism of formation of a hydrogen bond between a proton (Н . δ + ) and more electronegative sulfur atoms (:S δ - ), oxygen (:O δ - ) and nitrogen (:N δ - )

This connection is significantly weaker other chemical bonds ( energy her education 10-40 kJ / mol), and is mainly determined by electrostatic and donor-acceptor interactions.

The hydrogen bond can be like intramolecular and intermolecular.

2.1.4. Hydrophobic interactions

Before considering nature hydrophobic interaction, it is necessary to introduce the concept “ hydrophilic " and " hydrophobic " functional groups.

Groups that can form hydrogen bonds with water molecules are called hydrophilic.

These groups include polar groups: amino group (-NH 2 ) , carboxyl(- COOH), carbonyl group(- CHO) and sulfhydryl group ( - SH).

Usually, hydrophilic connections are good soluble in water. !!! This is due to the fact that polar groups are able to form hydrogen bonds with water molecules .

The emergence such links are accompanied by energy release, therefore, there is a tendency to maximizing the contact surface charged groups and water ( Rice. 2.3):

Rice. 2.3. Mechanism of formation of hydrophobic and hydrophilic interactions

Molecules or parts of molecules that are unable to form hydrogen bonds with water are called hydrophobic groups.

These groups include alkyl and aromatic radicals that non-polar and do not carry electric charge.

Hydrophobic groups – poorly or not at all soluble in water.

This is explained by atoms and groups of atoms included in hydrophobic groups are electrically neutral and therefore) can not form hydrogen bonds with water.

!!! Hydrophobic interactions result from contact between non-polar radicals that are unable to break hydrogen bonds between water molecules.

As a result water molecules crowded out to surface hydrophilic molecules ( Rice. 2.3).

2.1.5. Van der Waals interactions.

In molecules, there are also very weak and short-range attractive forces between electrically neutral atoms and functional groups.

These are the so-called van der Waals interactions.

They are due electrostatic interactionbetween negatively charged electrons oneatom and positively charged nucleus anotheratom.

Since the nuclei of atoms shielded their own electrons from the nuclei of neighboring atoms, then arising between different atoms van der Waals interactions very small.

All these types of interactions take part in the formation, maintaining and stabilization spatial structure ( conformations) protein molecules ( Rice. 2.4):

Rice. 2.4. Formation mechanism covalent bonds and weak non-covalent interactions:1 - electro-static interactions;2 - hydrogen bonds;3 - hydrophobic interactions,4 - disulfide bonds

Forces that contribute formation of the spatial structure of proteins and keeping it in a stable state are very weak forces... The energy of these forces on 2-3 less than the energy of covalent bonds. They act between individual atoms and groups of atoms.

However, the huge number of atoms in the molecules of biopolymers (proteins) leads to the fact that the total energy of these weak interactions becomes comparable to the energy of covalent bonds.

The presence in H 2 O molecules of lone electron pairs at oxygen atoms and positively charged hydrogen atoms leads to a very special interaction between the molecules, called HYDROGEN BOND (see figure). Unlike all the species already familiar to us chemical bond this bond is intermolecular.

A hydrogen bond (in the figure it is indicated by a dotted line) occurs when an electron-depleted hydrogen atom of one water molecule interacts with the lone electron pair of an oxygen atom of another water molecule.

Hydrogen bond is a special case intermolecular bonds... It is believed to be caused mainly by electrostatic forces. For a hydrogen bond to occur, it is necessary that the molecule contains one or more hydrogen atoms associated with small but electronegative atoms, for example: O, N, F. It is important that these electronegative atoms have lone electron pairs. Therefore, hydrogen bonds are characteristic of substances such as water H 2 O, ammonia NH 3, hydrogen fluoride HF. For example, HF molecules are linked by hydrogen bonds, which are shown in the figure with dashed lines:

Hydrogen bonds about 20 times less durable than covalent, but it is they who make water be liquid or ice (not gas) under normal conditions. Hydrogen bonds are destroyed only when liquid water turns into steam.

At temperatures above 0 ° C (but below the boiling point), water no longer has such an ordered intermolecular structure, as shown in the figure. Therefore, in liquid water, the molecules are linked together only in separate aggregates of several molecules. These units can move freely next to each other, forming a mobile liquid. But with decreasing temperature, the order becomes more and more, and the aggregates become larger and larger. Finally, ice forms, which has exactly the ordered structure shown in the figure.

Topic: BASIC CLASSES OF INORGANIC COMPOUNDS. CLASSIFICATION OF INORGANIC SUBSTANCES

Lecture plan:

1. The main classes of inorganic compounds.
2. Foundations. Chemical properties.
3. Oxides. Their types, Chemical properties.
4. Acids. Classification and their chemical properties.
5. Salt. Classification and their chemical properties.

Simple substances... Molecules are made up of atoms of one kind (atoms of one element). In chemical reactions, they cannot decompose with the formation of other substances.

Complex substances(or chemical compounds). Molecules are made up of atoms different kind(atoms of various chemical elements). In chemical reactions, they decompose to form several other substances.

There is no sharp boundary between metals and non-metals, because there is simple substances exhibiting dual properties.

Water molecules are linked through hydrogen bonds, the distance between oxygen and hydrogen atoms is 96 pm, and between two hydrogens - 150 pm. In the solid state, the oxygen atom participates in the formation of two hydrogen bonds with neighboring water molecules. In this case, individual H 2 O molecules are in contact with each other with opposite poles. Thus, layers are formed in which each molecule is associated with three molecules of its own layer and one of the adjacent one. As a result, the crystal structure of ice consists of hexagonal "tubes" interconnected like a honeycomb.

According to computer simulations, at a tube diameter of 1.35 nm and a pressure of 40,000 atmospheres, the hydrogen bonds were bent, leading to the formation of a double-walled helix. The inner wall of this structure is twisted into four coils, and the outer one consists of four double helices, similar to the structure of a DNA molecule.

The last fact leaves an imprint not only on the evolution of our ideas about water, but also on the evolution early life and the DNA molecule itself. If we assume that in the era of the origin of life, cryolite clay rocks were in the form of nanotubes, the question arises - could the water sorbed in them serve as a structural basis - a matrix for DNA synthesis and information reading? Perhaps that is why the spiral structure of DNA repeats the spiral structure of water in nanotubes. According to the journal New Scientist, now our foreign colleagues have to confirm the existence of such water macromolecules in real experimental conditions using infrared spectroscopy and neutron scattering spectroscopy.

Such studies of ice nanocrystals were carried out in 2007 by Mikaelides from the Center for Nanotechnology in London and Morgenstern from the University. Leibniz in Hanover (Fig. 36). They cooled water vapor above the surface of a metal plate at a temperature of 5 degrees Kelvin. Soon, using a scanning tunneling microscope, a hexamer (six interconnected water molecules), the smallest snowflake, was observed on the plate. It is the smallest possible ice cluster. The scientists also observed clusters containing seven, eight and nine molecules.

Rice . 36. Image of a water hexamer obtained using a scanning tunneling microscope. The hexamer is about 1 nm in diameter. Photo London Center for Nanotechnology

The development of a technology that made it possible to obtain an image of a water hexamer is an important scientific achievement in itself. For observation, it was necessary to reduce the probing current to a minimum, which made it possible to protect the weak bonds between individual water molecules from destruction due to the observation process. In addition, the work used theoretical approaches quantum mechanics... An integrated approach has produced impressive results.

Unlike crystalline ice, where the binding energy is the same between all water molecules, in nanoclusters there is an alternation of strong and weak bonds (and corresponding distances) between individual molecules. Important results were also obtained on the ability of water molecules to distribute hydrogen bonds and to bond them with the metal surface.

Theoretical analyzes of Oparin, experiments of Miller, Fox and others indisputably prove that organic molecules from inorganic ones can be structured in nature. The main source of energy in their experiments is heat. In nature, this is solar radiation and magma energy. Another very significant conclusion is that the origin of life can occur in an alkaline environment. In all cases, the self-organization of the living is observed.

In the XIX century. Pastior drew attention to the fact that in inanimate nature, molecules are symmetrical. And in living nature, there is a mirror asymmetry of molecules. Proteins are composed of levorotatory amino acids. This property is determined by the rotation of the molecule of the plane of polarization of light. How to explain the phenomenon?

It is possible that the presence of asymmetry in organic molecules manifested itself when the open system, which preceded the biosphere, was in an extremely non-equilibrium critical condition.

An abrupt evolutionary transition has occurred, which is characteristic feature self-organization. An example of this state is experiments where water molecules resemble DNA in nanotubes. The transition from symmetric molecules of inanimate nature to asymmetric biomolecules of living nature could occur at the initial stage of chemical evolution, as the self-organization of matter. Prof. Antonov proved that water is also an open system and exchanges energy and matter with environment(prof. Antonov, 1992).

Such extreme conditions are observed during volcanic activity, discharges in the atmosphere of the young Earth. Mineral water interacting with calcium carbonate, as well as sea water, are a favorable spectrum for the preservation of self-organizing structures. The Kirlian effect under laboratory conditions creates a selective discharge that allows one to observe the emission of light by atoms or molecules. Miller's experiments also create non-equilibrium extreme conditions with a gas discharge.

Kirlian aura - the plasma glow of an electric discharge is observed on the surface of objects in an alternating electric field of high frequency 10-100 kHz, at which surface tension arises between the electrode and the object under study from 5 to 30 kV. The Kirlian effect is observed like lightning or static discharge on any biological, organic objects, as well as on inorganic samples of various nature.

To visualize the Kirlian aura, a high alternating voltage with a high frequency is applied to the electrode - from 1 to 40 kilovolts at 200-15000 Hertz. The object itself serves as the other electrode. Both electrodes are separated by an insulator and a thin layer of air, the molecules of which are dissociated by a strong magnetic field between the electrode and the object. In this layer of air, located between the object and the electrode, three processes take place.

The first process is ionization and formation of atomic nitrogen.

The second process is the ionization of air molecules and the formation of an ion current - a corona discharge between the object and the electrode. The shape of the glow crown, its density, etc. are determined by the object's own electromagnetic radiation.

The third process is the transition of electrons from lower to higher energy levels and vice versa. With this transition of electrons, a quantum of light is emitted. The magnitude of the electron transition depends on the intrinsic electromagnetic field the object under study. Therefore, at different points of the field surrounding the object, the electrons receive different impulses, i.e. jump to different energy levels, which leads to the emission of light quanta of different lengths and energies. The latter are registered by the human eye or colored photographic paper as different colors, which, depending on the object, can color the glowing crown in different colors. These three processes in their totality give the big picture Kirlian effect, which allows you to study the electromagnetic field of an object. The Kirlian effect is thus associated with the bioelectric aura of a living object.