A metallic bond is formed between atoms. metal chemical bond
You learned how atoms of metal and non-metal elements interact with each other (electrons pass from the first to the second), as well as atoms of non-metal elements with each other (unpaired electrons of the outer electronic layers of their atoms combine into common electron pairs). Now we will get acquainted with how the atoms of metal elements interact with each other. Metals do not usually exist as isolated atoms, but as an ingot or piece of metal. What holds metal atoms together?
The atoms of most metal elements at the outer level contain a small number of electrons - 1, 2, 3. These electrons are easily detached, and the atoms turn into positive ions. The detached electrons move from one ion to another, binding them into a single whole.
It is simply impossible to figure out which electron belonged to which atom. All detached electrons became common. Connecting with ions, these electrons temporarily form atoms, then break off again and combine with another ion, etc. A process occurs endlessly, which can be represented by a diagram:
Consequently, in the volume of the metal, atoms are continuously converted into ions and vice versa. They are called atom-ions.
Figure 41 schematically shows the structure of a sodium metal fragment. Each sodium atom is surrounded by eight neighboring atoms.
Rice. 41.
Scheme of the structure of a fragment of crystalline sodium
The detached outer electrons freely move from one formed ion to another, connecting, as if gluing together, the ionic backbone of sodium into one giant metal crystal (Fig. 42).
Rice. 42.
Diagram of a metallic bond
The metallic bond has some similarities with the covalent bond, since it is based on the socialization of external electrons. However, in the formation of a covalent bond, the outer unpaired electrons of only two neighboring atoms are socialized, while in the formation of a metallic bond, all atoms participate in the socialization of these electrons. That is why crystals with a covalent bond are brittle, while those with a metal bond are, as a rule, plastic, electrically conductive, and have a metallic sheen.
Figure 43 shows an ancient golden figurine of a deer, which is already more than 3.5 thousand years old, but it has not lost its noble metallic luster, which is characteristic of gold - this most plastic of metals.
rice. 43. Golden deer. 6th century BC e.
A metallic bond is characteristic of both pure metals and mixtures of various metals - alloys that are in solid and liquid states. However, in the vapor state, metal atoms are bound together by a covalent bond (for example, yellow light lamps are filled with sodium vapor to illuminate the streets of large cities). Metal pairs consist of individual molecules (monatomic and diatomic).
The question of chemical bonds is the central question of the science of chemistry. You got acquainted with the initial ideas about the types of chemical bonds. In the future, you will learn a lot of interesting things about the nature of the chemical bond. For example, that in most metals, in addition to the metallic bond, there is also a covalent bond, that there are other types of chemical bonds.
Keywords and phrases
- Metal connection.
- Atom ions.
- Shared electrons.
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Questions and tasks
- A metallic bond has similarities with a covalent bond. Compare these chemical bonds with each other.
- The metallic bond has similarities with the ionic bond. Compare these chemical bonds with each other.
- How can the hardness of metals and alloys be increased?
- According to the formulas of substances, determine the type of chemical bond in them: Ba, BaBr 2, HBr, Br 2.
A metallic bond is a bond formed between atoms under conditions of strongly pronounced delocalization (the spread of valence electrons along several chemical bonds in a compound) and a shortage of electrons in an atom (crystal). It is unsaturated and spatially non-directional.
The delocalization of valence electrons in metals is a consequence of the multicenter nature of the metallic bond. The multicenter nature of the metallic bond ensures high electrical and thermal conductivity of metals.
Saturability determined by the number of valence orbitals involved in the formation of chemical. connections. Quantitative characteristic - valency. Valence - the number of bonds that one atom can form with others; - is determined by the number of valence orbitals involved in the formation of bonds by the exchange and donor-acceptor mechanism.
Orientation – the connection is formed in the direction of maximum overlap of electron clouds; - determines the chemical and crystal-chemical structure of a substance (how the atoms are connected in the crystal lattice).
When a covalent bond is formed, the electron density is concentrated between the interacting atoms (drawing from a notebook). In the case of a metallic bond, the electron density is delocalized over the entire crystal. (drawing from a notebook)
(example from notebook)
Due to the unsaturation and non-directional nature of the metallic bond, metallic bodies (crystals) are highly symmetrical and highly coordinated. The overwhelming majority of crystalline structures of a metal correspond to 3 types of atom packing in crystals:
1. HCC– Grenet-centered cubic close-packed structure. Packing density - 74.05%, coordination number = 12.
2. GPU– hexagonal close-packed structure, packing density = 74.05%, c.h. = 12.
3. BCC– volume is centered, packing density = 68.1%, k.ch. = 8.
A metallic bond does not preclude some degree of covalence. Metal bond in its pure form is typical only for alkali and alkaline earth metals.
A pure metallic bond is characterized by an energy of the order of 100/150/200 kJ/mol, which is 4 times weaker than the covalent one.
36. Chlorine and its properties. B \u003d 1 (III, IV, V and VII) oxidation state \u003d 7, 6, 5, 4, 3, 1, −1
greenish-yellow gas with a pungent, irritating odor. Chlorine occurs in nature only in the form of compounds. In nature, in the form of potassium chloride, magnesium, nitrium, formed as a result of the evaporation of former seas and lakes. Receipt.prom: 2NaCl + 2H2O \u003d 2NaOH + H2 + Cl2, by electrolysis of waters of chlorides Me.\2KMnO4 + 16HCl \u003d 2MnCl2 + 2KCl + 8H2O + 5Cl2 / Chemically, chlorine is very active, directly combines with almost all Me, and with non-metals (except carbon, nitrogen, oxygen, inert gases), replaces hydrogen in the pre-HC and joins unsaturated compounds, displaces bromine and iodine from their compounds. Phosphorus ignites in an atmosphere of chlorine PCl3, and with further chlorination - PCl5; sulfur with chlorine = S2Cl2, SCl2 and other SnClm. A mixture of chlorine and hydrogen burns. With oxygen, chlorine forms oxides: Cl2O, ClO2, Cl2O6, Cl2O7, Cl2O8, as well as hypochlorites (salts of hypochlorous acid), chlorites, chlorates and perchlorates. Everything oxygen compounds chlorine form explosive mixtures with easily oxidized substances. Chlorine oxides are unstable and can explode spontaneously, hypochlorites decompose slowly during storage, chlorates and perchlorates can explode under the influence of initiators. in water - hypochlorous and salt: Сl2 + Н2О = НClО + НCl. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl2 \u003d NaClO + NaCl + H2O, and when heated - chlorates. When ammonia reacts with chlorine, nitrogen trichloride is formed. with other halogens interhalogen compounds. Fluorides СlF, СlF3, СlF5 are very reactive; for example, in a ClF3 atmosphere, glass wool ignites spontaneously. Known compounds of chlorine with oxygen to fluorine are chlorine oxyfluorides: ClO3F, ClO2F3, ClOF, ClOF3 and fluorine perchlorate FClO4. Application: production of chemical compounds, water purification, synthesis in food, farm prom-ti-bactericide, antiseptic, whitening of papers, fabrics, pyrotechnics, matches, destroys weeds in CX.
Biological role: biogenic component of plant and animal tissues. 100g basic osmotic active substance blood plasma, lymph, cerebrospinal fluid and some tissues. Daily sodium chloride requirement = 6-9g - bread, meat and dairy products. Plays a role in water-salt metabolism, contributing to the retention of water by tissues. The regulation of acid-base balance in tissues is carried out along with other processes by changing the distribution of chlorine between the blood and other tissues, chlorine is involved in energy metabolism in plants, activating both oxidative phosphorylation and photophosphorylation. Chlorine has a positive effect on the absorption of oxygen by the roots, a component of the iron juice.
37. Hydrogen, water. B \u003d 1; st.oxide \u003d + 1-1 The hydrogen ion is completely devoid of electron shells; it can approach very close distances and be introduced into electron shells.
The most common element in the universe. It makes up the bulk of the Sun, stars and other cosmic bodies. It is relatively rare in the free state on Earth - it is found in petroleum and combustible gases, is present as inclusions in some minerals, and most of it is in the composition of water. Receipt: 1. Laboratory Zn+2HCl=ZnCl2+H 2 ; 2.Si + 2NaOH + H 2 O \u003d Na 2 SiO 3 + 2H 2; 3. Al + NaOH + H 2 O \u003d Na (AlOH) 4 + H 2. 4. In industry: conversion, electrolysis: СH4+H2O=CO+3H2\CO+H2O=CO+ H2/Chemistry. N.O.: H 2 + F 2 \u003d 2HF. When irradiated, illuminated, catalysts: H 2 + O 2, S, N, P \u003d H 2 O, H 2 S, NH 3, Ca + H2 \u003d CaH2 \ F2 + H2 \u003d 2HF \ N2 + 3H2 → 2NH3 \ Cl2 + H2 → 2HCl, 2NO+2H2=N2+2H2O,CuO+H2=Cu+H2O,CO+H2=CH3OH. Hydrogen forms hydrides: ionic, covalent and metallic. To ionic -NaH - &, CaH 2 - & + H 2 O \u003d Ca (OH) 2; NaH + H 2 O \u003d NaOH + H 2. Covalent -B 2 H 6, AlH 3, SiH 4. Metal - with d-elements; variable composition: MeH ≤1 , MeH ≤2 - are introduced into the voids between atoms. Conducts heat, current, solid. WATER.sp3-hybrid highly polar.molecule at an angle of 104.5 , dipoles, the most common solvent. Water reacts at room t: with active halogens (F, Cl) and interhaloid compounds with salts, forming a weak acid and a weak base, causing their complete hydrolysis ; with anhydrides and carboxylic and inorganic acid halides. kis-t; with active metalorgan-mi compounds; with carbides, nitrides, phosphides, silicides, active Me hydrides; with many salts, forming hydrates; with boranes, silanes; with ketenes, carbon suboxide; with noble gas fluorides. Water reacts when heated: with Fe, Mg with coal, methane; with some alkyl halides. Application:hydrogen - synthesis of ammonia, methanol, hydrogen chloride, TV fats, hydrogen flame - for welding, melting, in metallurgy for the reduction of Me from oxide, fuel for rockets, in pharmacy - water, peroxide antiseptic, bactericide, washing, hair bleaching, sterilization.
Biol.role: hydrogen-7kg, The main function of hydrogen is the structuring of biological space (water and hydrogen bonds) and the formation of a variety of org molecules (included in the structure of proteins, carbohydrates, fats, enzymes) Thanks to hydrogen bonds,
copying of the DNA molecule. Water takes part in a huge
the number of biochemical reactions, in all physiological and biological
processes, ensures the exchange of substances between the body and the environment, between
cells and within cells. Water is the structural basis of cells, necessary for
maintaining their optimal volume, it determines the spatial structure and
functions of biomolecules.
As a result of electrostatic attraction between the cation and the anion, a molecule is formed.
Ionic bond
The ionic bond theory was proposed in 1916 ᴦ. German scientist W. Kossel. This theory explains the formation of links between atoms of typical metals and atoms typical non-metals: CsF, CsCl, NaCl, KF, KCl, Na 2 O, etc.
According to this theory, when an ionic bond is formed, the atoms of typical metals donate electrons, and the atoms of typical non-metals accept electrons.
As a result of these processes, metal atoms are converted into positively charged particles, which are called positive ions or cations; and the atoms of non-metals turn into negative ions - anions. The charge of the cation is equal to the number of donated electrons.
Metal atoms donate electrons to the outer layer, and the resulting ions have complete electronic structures (pre-outer electron layer).
The value of the negative charge of the anion is equal to the number of received electrons.
Atoms of non-metals accept as many electrons as they need to completion of an electronic octet (outer electronic layer).
For example: general scheme formation of the NaCl molecule from Na and C1 atoms: Na°-le = Na +1 Formation of ions
Cl ° + 1e - \u003d Cl -
Na +1 + Cl - \u003d Na + Cl -
Na ° + Cl ° \u003d Na + Cl - Connection of ions
· The bond between ions is called an ionic bond.
Compounds that consist of ions are called ionic compounds.
The algebraic sum of the charges of all ions in the molecule of the ionic compound must be equal to zero, because any molecule is an electrically neutral particle.
There is no sharp boundary between ionic and covalent bonds. An ionic bond can be considered as an extreme case of a polar covalent bond, during the formation of which a common electron pair completely moves towards an atom with a higher electronegativity.
The atoms of most typical metals have a small number of electrons on the outer electron layer (typically 1 to 3); these electrons are called valence electrons. In metal atoms, the bond strength of valence electrons with the nucleus is low, that is, the atoms have a low ionization energy. This makes it easy to lose valence electrons h transformation of metal atoms into positively charged ions (cations):
Me ° -ne ® Me n +
In the crystal structure of a metal, valence electrons have the ability to easily move from one atom to another, which leads to the socialization of electrons by all neighboring atoms. Simplified, the structure of a metal crystal is presented as follows: at the nodes of the crystal lattice there are Me p + ions and Me ° atoms, and valence electrons move relatively freely between them, making a connection between all atoms and metal ions (Fig. 3). This is a special type of chemical bond called a metallic bond.
· Metallic bond - a bond between atoms and ions of metals in the crystal lattice, carried out by socialized valence electrons.
Due to this type of chemical bond, metals have a certain set of physical and chemical properties that distinguish them from non-metals.
Rice. 3. Scheme of the crystal lattice of metals.
The strength of the metal bond ensures the stability of the crystal lattice and the plasticity of metals (the ability to undergo various processing without destruction). The free movement of valence electrons allows metals to conduct electricity and heat well. The ability to reflect light waves (ᴛ.ᴇ. metallic luster) is also explained by the structure of the crystal lattice of the metal.
Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, the most characteristic physical properties of metals based on the presence of a metallic bond are:
■crystal structure;
■metallic luster and opacity;
■plasticity, malleability, fusibility;
■high electrical and thermal conductivity; and tendency to form alloys.
Metal bond - concept and types. Classification and features of the category "Metal connection" 2017, 2018.
The very name "metal bond" indicates that we are talking about the internal structure of metals. Atoms of most metals on the outer energy level contain a small number of valence electrons compared to total number external energetically close ... .
The metallic bond is based on the socialization of valence electrons belonging not to two, but to almost all metal atoms in a crystal. There are far fewer valence electrons in metals than there are free orbitals. This creates conditions for free movement ... .
Essential information about the nature of the chemical bond in metals can be obtained on the basis of two characteristic features compared to covalent and ionic compounds. Metals, firstly, differ from other substances in high electrical conductivity and ....
Significant information about the nature of the chemical bond in metals can be obtained on the basis of two characteristic features for them in comparison with covalent and ionic compounds. Metals, firstly, differ from other substances in high electrical conductivity and ....
A molecule is the smallest particle of a substance that has its chemical properties. According to the theory of chemical bonding, the stable state of an element corresponds to a structure with electronic formula outer level s2p6 (argon, krypton, radon, and others). While educating...
All currently known chemical elements located in the periodic table are conditionally divided into two large groups: metals and non-metals. In order for them to become not just elements, but connections, chemicals, could interact with each other, they must exist in the form of simple and complex substances.
It is for this that some electrons are trying to accept, while others - to give. Replenishing each other in this way, the elements form various chemical molecules. But what keeps them together? Why are there substances of such strength that even the most serious tools cannot destroy? And others, on the contrary, are destroyed by the slightest impact. All this is explained by the formation of various types of chemical bonds between atoms in molecules, the formation of a crystal lattice of a certain structure.
Types of chemical bonds in compounds
In total, 4 main types of chemical bonds can be distinguished.
- Covalent non-polar. It is formed between two identical non-metals due to the socialization of electrons, the formation of common electron pairs. Valence unpaired particles take part in its formation. Examples: halogens, oxygen, hydrogen, nitrogen, sulfur, phosphorus.
- covalent polar. It is formed between two different non-metals or between a metal that is very weak in properties and a non-metal that is weak in electronegativity. It is also based on common electron pairs and their pulling towards oneself by that atom, whose electron affinity is higher. Examples: NH 3, SiC, P 2 O 5 and others.
- Hydrogen bond. The most unstable and weak, it is formed between a strongly electronegative atom of one molecule and a positive one of another. Most often this happens when substances are dissolved in water (alcohol, ammonia, and so on). Thanks to this connection, macromolecules of proteins, nucleic acids, complex carbohydrates, and so on can exist.
- Ionic bond. It is formed due to the forces of electrostatic attraction of differently charged ions of metals and non-metals. The stronger the difference in this indicator, the more pronounced is the ionic nature of the interaction. Examples of compounds: binary salts, complex compounds - bases, salts.
- A metallic bond, the mechanism of formation of which, as well as properties, will be discussed further. It is formed in metals, their alloys of various kinds.
There is such a thing as the unity of a chemical bond. It just says that it is impossible to consider every chemical bond as a reference. They are all just nominal units. After all, all interactions are based on a single principle - electron static interaction. Therefore, ionic, metallic, covalent bonds and hydrogen bonds have a single chemical nature and are only boundary cases of each other.
Metals and their physical properties
Metals are in the vast majority among all chemical elements. This is due to their special properties. Most of them were obtained by man nuclear reactions under laboratory conditions, they are radioactive with a short half-life.
However, the majority are natural elements that form whole rocks and ores and are part of most important compounds. It was from them that people learned to cast alloys and make a lot of beautiful and important products. These are such as copper, iron, aluminum, silver, gold, chromium, manganese, nickel, zinc, lead and many others.
For all metals, there are common physical properties, which explains the scheme for the formation of a metallic bond. What are these properties?
- malleability and plasticity. It is known that many metals can be rolled even to the state of foil (gold, aluminum). From others, wire, metal flexible sheets, products that can be deformed under physical impact, but immediately restore their shape after its termination, are obtained. It is these qualities of metals that are called malleability and ductility. The reason for this feature is the metallic type of connection. Ions and electrons in a crystal slide relative to each other without breaking, which makes it possible to maintain the integrity of the entire structure.
- Metallic sheen. It also explains the metallic bond, the mechanism of formation, its characteristics and features. So, not all particles are able to absorb or reflect light waves of the same wavelength. The atoms of most metals reflect short-wavelength rays and acquire almost the same color of silver, white, pale bluish. The exceptions are copper and gold, their color is reddish-red and yellow, respectively. They are able to reflect longer wavelength radiation.
- Thermal and electrical conductivity. These properties are also explained by the structure of the crystal lattice and the fact that a metallic type of bond is realized in its formation. Due to the "electron gas" moving inside the crystal, electricity and heat is instantly and evenly distributed among all atoms and ions and conducted through the metal.
- Solid state of aggregation at normal conditions. The only exception here is mercury. All other metals are necessarily durable, solid connections as well as their alloys. It is also a result of the presence of a metallic bond in metals. The mechanism of formation of this type of particle binding fully confirms the properties.
These are the main physical characteristics for metals, which explains and defines exactly the scheme of formation of a metallic bond. This method of connecting atoms is relevant specifically for elements of metals, their alloys. That is, for them in the solid and liquid state.
Metal type chemical bond
What is its peculiarity? The thing is that such a bond is formed not due to differently charged ions and their electrostatic attraction, and not due to the difference in electronegativity and the presence of free electron pairs. That is, ionic, metallic, covalent bonds have a slightly different nature and distinctive features of the particles being bound.
All metals have the following characteristics:
- a small number of electrons per (except for some exceptions, which may have 6.7 and 8);
- large atomic radius;
- low ionization energy.
All this contributes to the easy separation of external unpaired electrons from the core. In this case, the atom has a lot of free orbitals. The scheme for the formation of a metallic bond will just show the overlap of numerous orbital cells of different atoms with each other, which, as a result, form a common intracrystalline space. Electrons are fed into it from each atom, which begin to wander freely in different parts of the lattice. Periodically, each of them attaches to an ion at a crystal site and turns it into an atom, then detaches again, forming an ion.
Thus, a metallic bond is a bond between atoms, ions and free electrons in a common metal crystal. An electron cloud that moves freely within a structure is called an "electron gas". It explains most of the metals and their alloys.
How concretely implements itself metal chemical bond? Various examples can be given. Let's try to consider on a piece of lithium. Even if you take it the size of a pea, there will be thousands of atoms. Let's imagine that each of these thousands of atoms donates its single valence electron to the common crystalline space. At the same time, knowing the electronic structure of a given element, one can see the number of empty orbitals. Lithium will have 3 of them (p-orbitals of the second energy level). Three for each atom out of tens of thousands - this is the common space inside the crystal, in which the "electron gas" moves freely.
A substance with a metallic bond is always strong. After all, the electron gas does not allow the crystal to collapse, but only shifts the layers and immediately restores. It shines, has a certain density (most often high), fusibility, malleability and plasticity.
Where else is a metallic bond realized? Substance examples:
- metals in the form of simple structures;
- all metal alloys with each other;
- all metals and their alloys in liquid and solid state.
There are just an incredible number of specific examples, because metals in periodic system over 80!
Metal bond: formation mechanism
If considered in general view, we have already outlined the main points above. The presence of free electrons and those easily detached from the nucleus due to the low ionization energy are the main conditions for the formation of this type of bond. Thus, it turns out that it is implemented between the following particles:
- atoms in the nodes of the crystal lattice;
- free electrons, which were valence in the metal;
- ions at the sites of the crystal lattice.
The end result is a metallic bond. The mechanism of formation in general terms is expressed by the following notation: Me 0 - e - ↔ Me n+. It is obvious from the diagram which particles are present in the metal crystal.
The crystals themselves may different shape. It depends on the specific substance we are dealing with.
Types of metal crystals
This structure of a metal or its alloy is characterized by a very dense packing of particles. It is provided by ions at the nodes of the crystal. Lattices themselves can be of different geometric shapes in space.
- Volume-centric cubic lattice - alkali metals.
- Hexagonal compact structure - all alkaline earths except barium.
- Face-centric cubic - aluminum, copper, zinc, many transition metals.
- Rhombohedral structure - in mercury.
- Tetragonal - indium.
The lower it is located in the periodic system, the more complex its packing and the spatial organization of the crystal. In this case, the metallic chemical bond, examples of which can be given for each existing metal, is decisive in the construction of a crystal. Alloys have a very diverse organization in space, some of which are still not fully understood.
Communication characteristics: non-directional
Covalent and metallic bonds have one very pronounced distinguishing feature. Unlike the first, the metallic bond is not directional. What does it mean? That is, the electron cloud inside the crystal moves completely freely within its limits in different directions, each of the electrons is able to join absolutely any ion at the nodes of the structure. That is, the interaction is carried out in different directions. Hence, they say that the metallic bond is non-directional.
The mechanism of covalent bonding implies the formation of common electron pairs, that is, clouds of overlapping atoms. Moreover, it occurs strictly along a certain line connecting their centers. Therefore, they talk about the direction of such a connection.
Saturability
This characteristic reflects the ability of atoms to have limited or unlimited interaction with others. So, the covalent and metallic bonds in this indicator are again opposites.
The first one is saturable. The atoms participating in its formation have a strictly defined number of valence outer electrons that are directly involved in the formation of the compound. More than it is, it will not have electrons. Therefore, the number of bonds formed is limited by valency. Hence the saturation of the connection. Due to this characteristic, most compounds have a constant chemical composition.
Metallic and hydrogen bonds, on the other hand, are unsaturable. This is due to the presence of numerous free electrons and orbitals inside the crystal. Ions also play a role in the nodes of the crystal lattice, each of which can become an atom and again an ion at any time.
Another characteristic of a metallic bond is the delocalization of the internal electron cloud. It manifests itself in the ability of a small number of common electrons to connect many atomic nuclei metals. That is, the density seems to be delocalized, distributed evenly between all links of the crystal.
Examples of bond formation in metals
Let's look at a few specific options that illustrate how a metallic bond is formed. Examples of substances are as follows:
- zinc;
- aluminum;
- potassium;
- chromium.
Formation of a metallic bond between zinc atoms: Zn 0 - 2e - ↔ Zn 2+. The zinc atom has four energy levels. Free orbitals, based on the electronic structure, it has 15 - 3 in p-orbitals, 5 in 4d and 7 in 4f. Electronic structure the following: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 0 4d 0 4f 0 , there are 30 electrons in the atom. That is, two free valence negative particles are able to move within 15 spacious and unoccupied orbitals. And so it is with every atom. As a result - a huge common space, consisting of empty orbitals, and a small number of electrons that bind the entire structure together.
Metal bond between aluminum atoms: AL 0 - e - ↔ AL 3+. The thirteen electrons of an aluminum atom are located on three energy levels, which they obviously have in excess. Electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 1 3d 0 . Free orbitals - 7 pieces. Obviously, the electron cloud will be small compared to the total internal free space in the crystal.
Chromium metal bond. This element is special in its electronic structure. Indeed, to stabilize the system, the electron falls from 4s to the 3d orbital: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 4p 0 4d 0 4f 0 . There are 24 electrons in total, of which six are valence. It is they who go into the common electronic space to form a chemical bond. There are 15 free orbitals, which is still much more than is required to fill. Therefore, chromium is also a typical example of a metal with a corresponding bond in the molecule.
One of the most active metals, reacting even with ordinary water with ignition, is potassium. What explains these properties? Again, in many ways - a metallic type of connection. This element has only 19 electrons, but they are already located at 4 energy levels. That is, on 30 orbitals of different sublevels. Electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 0 4p 0 4d 0 4f 0 . Just two with very low ionization energy. Freely come off and go into the common electronic space. There are 22 orbitals to move one atom, that is, a very large free space for the "electron gas".
Similarities and differences with other types of relationships
Generally this question already discussed above. We can only generalize and draw a conclusion. The main distinguishing features of metal crystals from all other types of communication are:
- several types of particles involved in the binding process (atoms, ions or atom-ions, electrons);
- different spatial geometric structure of crystals.
With hydrogen and ionic bonds, the metal bond is unsaturable and non-directional. With a covalent polar - a strong electrostatic attraction between the particles. Separately from the ionic - the type of particles in the nodes of the crystal lattice (ions). With covalent non-polar - atoms at the nodes of the crystal.
Types of bonds in metals of different state of aggregation
As we noted above, the metallic chemical bond, examples of which are given in the article, is formed in two states of aggregation of metals and their alloys: solid and liquid.
The question arises: what type of bond in metal vapors? Answer: covalent polar and non-polar. As in all compounds that are in the form of a gas. That is, with prolonged heating of the metal and its transfer from a solid state to a liquid, the bonds do not break and the crystalline structure is preserved. However, when it comes to transferring a liquid to a vapor state, the crystal is destroyed and the metallic bond is converted into a covalent one.
In the monatomic state under normal conditions, only noble gases are found. The remaining elements do not exist in the form of an individual, as they have the ability to interact with each other or with other atoms. In this case, more complex particles are formed.
In contact with
A set of atoms can form the following particles:
- molecules;
- molecular ions;
- free radicals.
Types of chemical interaction
The interaction between atoms is called a chemical bond. The basis is electrostatic forces (forces of interaction of electric charges) that act between atoms, the carriers of these forces are the nucleus of an atom and electrons.
The electrons located at the external energy level play the main role in the formation of chemical bonds between atoms. They are the most remote from the core, and, consequently, are associated with it the least firmly. They are called valence electrons.
Particles interact with each other in various ways, which leads to the formation of molecules (and substances) of different structures. Distinguish the following types chemical bond:
- ionic;
- covalent;
- van der Waals;
- metal.
Speaking of various types chemical interaction between atoms, it is worth remembering that all types are equally based on the electrostatic interaction of particles.
metal chemical bond
As can be seen from the position of metals in the table of chemical elements, they, for the most part, have a small number of valence electrons. The electrons are bound to their nuclei rather weakly and are easily detached from them. As a result, positively charged metal ions and free electrons are formed.
These electrons, freely moving in the crystal lattice, are called "electron gas".
The figure schematically shows the structure of a metal substance.
That is, in the volume of the metal, atoms constantly turn into ions (they are called atom-ions), and vice versa, ions constantly receive electrons from the "electron gas".
The mechanism of formation of a metallic bond can be written as a formula:
atom M 0 - ne ↔ ion M n+
Thus, metals are positive ions, which are located in the crystal lattice in certain positions, and electrons, which can move freely enough between atom-ions.
The crystalline grid represents the "skeleton", the core of matter, and electrons move between its nodes. The forms of crystal lattices of metals can be different, for example:
- the volume-centric cubic lattice is characteristic of alkali metals;
- face-centric cubic lattice have, for example, zinc, aluminum, copper, and other transition elements;
- the hexagonal shape is typical for alkaline earth elements (an exception is barium);
- tetragonal structure - in indium;
- rhombohedral - in mercury.
An example of a metal crystal lattice is shown in the picture below..
Differences from other types
A metallic bond differs from a covalent bond in strength. The energy of metallic bonds is less than covalent ones by 3–4 times and less ionic bond energy.
In the case of a metallic bond, one cannot speak of directionality, the covalent bond is strictly directed in space.
Such a characteristic as saturation is also not typical for the interaction between metal atoms. While covalent bonds are saturable, that is, the number of atoms that can interact with is strictly limited by the number of valence electrons.
Communication diagram and examples
The process occurring in the metal can be written using the formula:
K - e<->K+
Al-3e<->Al 3+
Na-e<->Na+
Zn - 2e<->Zn2+
Fe-3e<->Fe3+
If we describe in more detail the metallic bond, how this type of bond is formed, it is necessary to consider the structure of the external energy levels of the element.
An example is sodium. The only valence 3s electron present at the outer level can freely move along the free orbitals of the third energy level. When sodium atoms approach each other, the orbitals overlap. Now all electrons can move between atom-ions within all interlocked orbitals.
Zinc has 2 valence electrons as many as 15 free orbitals in the fourth energy level. When atoms interact, these free orbitals will overlap, as if socializing the electrons that move along them.
Chromium atoms have 6 valence electrons and all of them will participate in the formation of an electron gas and bind atom ions.
A special type of interaction, which is characteristic of metal atoms, determines a number of properties that unite them and distinguish metals from other substances. Examples of such properties are high melting points, high boiling points, malleability, ability to reflect light, high electrical and thermal conductivity.
The high melting and boiling points are explained by the fact that the metal cations are strongly bound by the electron gas. At the same time, a regularity is traced that the bond strength increases with an increase in the number of valence electrons. For example, rubidium and potassium are low-melting substances (melting points of 39 and 63 degrees Celsius, respectively), compared to, for example, chromium (1615 degrees Celsius).
The uniform distribution of valence electrons in a crystal explains, for example, such a property of metals as plasticity - the displacement of ions and atoms in any direction without destroying the interaction between them.
The free movement of electrons in atomic orbitals also explains the electrical conductivity of metals. Electron gas when applying a difference potentials goes from chaotic motion to directed motion.
In industry, not pure metals are often used, but their mixtures, called alloys. In an alloy, the properties of one component usually successfully complement the properties of another.
The metallic type of interaction is characteristic of both pure metals and their mixtures - alloys in solid and liquid states. However, if the metal is transferred to a gaseous state, then the bond between its atoms will be covalent. The metal in the form of a vapor consists of individual molecules (one- or two-atomic).
