Due to which a chemical bond is formed. Metallic and hydrogen chemical bonds

In the lesson, several types of chemical bonds will be considered: metallic, hydrogen and van der Waals, and you will also learn how physical and chemical properties depend on different types of chemical bonds in a substance.

Topic: Types of chemical bonds

Lesson: Metallic and Hydrogen Chemical Bonding

1. Metal bond

Metal bond -this is a type of bond in metals and their alloys between atoms or metal ions and relatively free electrons (electron gas) in a crystal lattice.

Metals are chemical elements with low electronegativity, so they easily give up their valence electrons. If there is a non-metal near the metal element, then the electrons from the metal atom are transferred to the non-metal. This type of bond is called ionic (Fig. 1).

Fig. 1. The formation of ionic bonds

In the case of simple substances of metals or their alloys, the situation changes.

When molecules are formed, the electron orbitals of the metals do not remain unchanged. They interact with each other, forming a new molecular orbital. Depending on the composition and structure of the compound, molecular orbitals can be both close to the set of atomic orbitals, and significantly differ from them. When the electron orbitals of the metal atoms interact, molecular orbitals are formed. Such that the valence electrons of a metal atom can move freely along these molecular orbitals. There is no complete separation of the charge, i.e. metal  is not a collection of cations and electrons floating around. But this is not a collection of atoms, which sometimes transform into a cationic form and transfer their electron to another cation. The real situation is a combination of these two extreme options.

The essence of the formation of a metal bond  consists of the following: metal atoms donate external electrons, and some of them turn into positively charged ions. Electrons detached from atoms move relatively freely between the positive metal ions that have appeared. A metallic bond arises between these particles, i.e. electrons, as it were, cement positive ions in a metal lattice (Fig. 2).

2. Physical properties of metals

The presence of a metal bond causes the physical properties of metals:

· High ductility

· Heat and electrical conductivity

· Metallic shine

Plastic- it is the ability of the material to easily deform under the action of a mechanical load. The metal bond is realized between all the atoms of the metal at the same time; therefore, the mechanical action on the metal does not break the specific bonds, but only the position of the atom changes. Atoms of a metal that are not connected by rigid bonds between themselves can, as it were, slide along a layer of electron gas, as happens when one glass slides over another with a layer of water between them. Due to this, metals can be easily deformed or rolled into thin foil. The most ductile metals are pure gold, silver and copper. All these metals are found in nature in the native form in varying degrees of purity. Fig. 3

Fig. 3. Metals found in nature in the native form

From them, especially of gold, are made various jewelry. Due to its amazing plasticity, gold is used in the decoration of palaces. From it you can roll out the foil with a thickness of only 3.10-3 mm. It is called gold leaf, applied to plaster, moldings or other objects.

Heat and electrical conductivity. Copper, silver, gold and aluminum conduct electricity best. But since gold and silver are expensive metals, cheaper copper and aluminum are used to make cables. The worst electrical conductors are manganese, lead, mercury and tungsten. In tungsten, the electrical resistance is so great that when it passes an electric current, it begins to glow. This property is used in the manufacture of incandescent lamps.

Body temperature is a measure of the energy of its constituent atoms or molecules. The electron gas of a metal can rather quickly transfer excess energy from one ion or atom to another. The temperature of the metal is quickly equalized throughout the volume, even if heating is on one side. This is observed, for example, if you drop a metal spoon into the tea.

Metallic shine.  Glitter is the body's ability to reflect light rays. Silver, aluminum and palladium have high light reflectivity. Therefore, it is these metals that are applied with a thin layer to the surface of the glass when making headlights, spotlights and mirrors.

Hydrogen bond

Consider the boiling point and melting point of hydrogen compounds of chalcogens: oxygen, sulfur, selenium and tellurium. Fig. four.

If we mentally extrapolate the direct boiling points and melting points of hydrogen compounds of sulfur, selenium and tellurium, then we will see that the melting point of water should be approximately -100 ° С, and boiling approximately 8 ° С. This happens because there is an interaction between water molecules - hydrogen bond,  which is unites  water molecules   in association.   For the destruction of these associates requires additional energy.

3. The mechanism of hydrogen bond formation

The hydrogen bond is formed between a highly polarized, possessing a significant proportion of the positive charge of a hydrogen atom and another atom with a very high electronegativity: fluorine, oxygen or nitrogen. Examples of substances capable of forming a hydrogen bond are shown in fig. five.

Consider the formation of hydrogen bonds between water molecules.  The hydrogen bond is represented by three dots. The emergence of hydrogen bonds due to the unique feature of the hydrogen atom. Since the hydrogen atom contains only one electron, when a common electron pair is pulled off by another atom, the nucleus of the hydrogen atom becomes bare, the positive charge of which acts on the electronegative elements in the substance molecules.

Compare properties ethyl alcohol and dimethyl ether. Based on the structure of these substances, it follows that ethyl alcohol can form intermolecular hydrogen bonds. This is due to the presence of a hydroxyl group. Dimethyl ether of intermolecular hydrogen bonds cannot form.

We compare their properties in table 1.

T kip., T PL, the solubility in water is higher in ethyl alcohol. This is a general pattern for substances between which molecules a hydrogen bond is formed. These substances are characterized by higher T kip., T PL, solubility in water and lower volatility.

Physical properties  compounds also depend on the molecular weight of the substance. Therefore, a comparison of the physical properties of substances with hydrogen bonds is legitimate only for substances with similar molecular masses.

The energy of a single hydrogen bond is about 10 times less than the energy of a covalent bond. If in organic molecules of complex composition there are several functional groups capable of forming a hydrogen bond, then they can form intramolecular hydrogen bonds (proteins, DNA, amino acids, orthonitrophenol, etc.). Due to the hydrogen bond, a secondary structure of proteins is formed, a double helix of DNA.

4. Van der Waals forces

Van der Waals connection.

Recall the noble gases. Helium compounds have not yet been obtained. He is not able to form ordinary chemical bonds.

At strongly negative temperatures, liquid and even solid helium can be obtained. In the liquid state, helium atoms are held by electrostatic attraction forces. There are three variants of these forces:

· Orientation forces. This is the interaction between two dipoles (HCl)

· Induction attraction. This is the attraction of a dipole and a non-polar molecule.

· Dispersive attraction. This is the interaction between two non-polar molecules (He). It occurs due to the uneven motion of electrons around the nucleus.

Summing up the lesson

In the lesson, three types of chemical bonding are considered: metallic, hydrogen and van der Waals. The dependence of physical and chemical properties on different types of chemical bonds in a substance was explained.

Bibliography

1. Rudzitis G. Ye. Chemistry. Basics of general chemistry. Grade 11: textbook for educational institutions: basic level / G. E. Rudzitis, FG Feldman. - 14th ed. - M .: Enlightenment, 2012.

2. Popel P. P. Chemistry: 8 class.: Textbook for secondary schools / P. P. Popel, L. S. Krivlya. - К .: ИЦ "Academy", 2008. - 240 p.: Ill.

3. Gabrielyan O. S. Chemistry. Grade 11. A basic level of. 2nd ed., Sr. - M .: Drofa, 2007. - 220 p.

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Homework

1. №№ 2, 4, 6 (p. 41) Rudzitis G. E. Chemistry. Basics of general chemistry. Grade 11: textbook for educational institutions: basic level / G. E. Rudzitis, FG Feldman. - 14th ed. - M .: Enlightenment, 2012.

2. Why for the manufacture of incandescent hairs using tungsten?

3. What explains the lack of hydrogen bonds in the molecules of aldehydes?

"Properties of chemical bonding"  - Metal crystal lattice. Dipole. Types of chemical bonds. The length of the connection. The main types of relationships. Hydrogen bond. The excited state of the atom. Communication characteristics. Forces. Electronic configurations. Ionic crystal lattice. Covalent bond Atomic crystal lattice. Basics of Chemistry.

"Metal chemical bond"  - Thermal conductivity - due to the high mobility. Gold products. Mercury, silver, palladium, aluminum possess high reflectivity. In metal bonding, the general with: ionic ion formation. Gold, copper, and silver are the most plastic. Metal chemical bond. The best conductors are copper and silver.

"The degree of oxidation of compounds" - The names of binary compounds. Determine the degree of oxidation of elements in compounds. Formulate binary compounds. The degree of oxidation of elements. Positive oxidation state. Binary connection. Element. Iron oxide. Formulate substances. Possible negative oxidation states. Oxidation state

"Types of chemical bonds"  - Substances fusible, often have a smell. The atomic framework has high strength. Metal bond. Ion bond. Covalent polar bond is formed between the atoms of various non-metals. ION CONNECTION formed by electrostatic attraction. Atoms. Held by weak intermolecular forces.

"Chemistry" Chemical bond ""  - There are no sharp boundaries between different types of chemical bonds. The number of common electron pairs is equal to the number of bonds between two atoms. Substance with covalent bond. Parameters of covalent bond. Types of chemical bonds and types of crystal lattices. Covalent bond Metals form metallic crystal lattices.

"The main types of chemical bonds"  - Mechanisms of breaking covalent bonds. Coordination. Polarity of communication. Metal bond. Connections Saturability. Directivity Mechanisms of covalent bond formation. The interaction of atoms in chemical compounds. Ionic chemical bond. The formation of an ionic chemical bond. Chemical bond Na + Cl.

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