Metal connection. Properties of metallic bond.
A metallic bond is a chemical bond caused by the presence of relatively free electrons. Characteristic of both pure metals and their alloys and intermetallic compounds.
Metal link mechanism
Positive metal ions are located at all nodes of the crystal lattice. Between them, valence electrons move randomly, like gas molecules, detached from the atoms during the formation of ions. These electrons act as cement, holding the positive ions together; otherwise, the lattice would disintegrate under the influence of repulsive forces between the ions. At the same time, electrons are held by ions within the crystal lattice and cannot leave it. The coupling forces are not localized or directed. For this reason, in most cases high coordination numbers appear (for example, 12 or 8). When two metal atoms come close together, the orbitals in their outer shells overlap to form molecular orbitals. If a third atom approaches, its orbital overlaps with the orbitals of the first two atoms, resulting in another molecular orbital. When there are many atoms, a huge number of three-dimensional molecular orbitals arise, extending in all directions. Due to multiple overlapping orbitals, the valence electrons of each atom are influenced by many atoms.
Characteristic crystal lattices
Most metals form one of the following highly symmetrical lattices with close packing of atoms: body-centered cubic, face-centered cubic, and hexagonal.
In a body-centered cubic (bcc) lattice, the atoms are located at the vertices of the cube and one atom is at the center of the cube volume. Metals have a cubic body-centered lattice: Pb, K, Na, Li, β-Ti, β-Zr, Ta, W, V, α-Fe, Cr, Nb, Ba, etc.
In a face-centered cubic (fcc) lattice, the atoms are located at the vertices of the cube and at the center of each face. Metals of this type have a lattice: α-Ca, Ce, α-Sr, Pb, Ni, Ag, Au, Pd, Pt, Rh, γ-Fe, Cu, α-Co, etc.
In a hexagonal lattice, the atoms are located at the vertices and center of the hexagonal bases of the prism, and three atoms are located in the middle plane of the prism. Metals have this packing of atoms: Mg, α-Ti, Cd, Re, Os, Ru, Zn, β-Co, Be, β-Ca, etc.
Other properties
Freely moving electrons cause high electrical and thermal conductivity. Substances that have a metallic bond often combine strength with plasticity, since when atoms are displaced relative to each other, the bonds do not break. Another important property is metallic aromaticity.
Metals conduct heat and electricity well, they are strong enough, and can be deformed without destruction. Some metals are malleable (they can be forged), some are malleable (you can draw wire from them). These unique properties are explained by a special type of chemical bond that connects metal atoms to each other - a metallic bond.
Metals in the solid state exist in the form of crystals of positive ions, as if “floating” in a sea of electrons freely moving between them.
Metallic bond explains the properties of metals, in particular their strength. Under the influence of a deforming force, a metal lattice can change its shape without cracking, unlike ionic crystals.
The high thermal conductivity of metals is explained by the fact that if a piece of metal is heated on one side, the kinetic energy of the electrons will increase. This increase in energy will spread in the “electron sea” throughout the sample at high speed.
The electrical conductivity of metals also becomes clear. If a potential difference is applied to the ends of a metal sample, the cloud of delocalized electrons will shift in the direction of the positive potential: this flow of electrons moving in one direction represents the familiar electric current.
Metal connection. Properties of metallic bond. - concept and types. Classification and features of the category "Metallic bond. Properties of metallic bond." 2017, 2018.
All currently known chemical elements located on the periodic table are divided into two large groups: metals and non-metals. In order for them to become not just elements, but compounds, chemical substances, and be able to interact with each other, they must exist in the form of simple and complex substances.
This is why some electrons try to accept, while others try to give away. By replenishing each other in this way, the elements form various chemical molecules. But what keeps them together? Why do there exist substances of such strength that even the most serious instruments cannot be destroyed? 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, there are 4 main types of chemical bonds.
- Covalent non-polar. It is formed between two identical non-metals due to the sharing 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. Formed between two different non-metals or between a metal with very weak properties and a non-metal with weak electronegativity. It is also based on common electron pairs and the pulling of them toward itself by the atom whose electron affinity is higher. Examples: NH 3, SiC, P 2 O 5 and others.
- Hydrogen bond. The most unstable and weakest, it is formed between a highly electronegative atom of one molecule and a positive atom of another. Most often this happens when substances are dissolved in water (alcohol, ammonia, etc.). 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 metal and non-metal ions. The stronger the difference in this indicator, the more clearly the ionic nature of the interaction is expressed. Examples of compounds: binary salts, complex compounds - bases, salts.
- A metal bond, the formation mechanism of which, as well as its properties, will be discussed further. It is formed in metals and 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 standard. They are all just conventionally designated units. After all, all interactions are based on a single principle - electron-static interaction. Therefore, ionic, metallic, covalent and hydrogen bonds have the same chemical nature and are only borderline cases of each other.
Metals and their physical properties
Metals are found in the overwhelming majority of all chemical elements. This is due to their special properties. A significant part of them was obtained by humans through nuclear reactions in laboratory conditions; they are radioactive with a short half-life.
However, the majority are natural elements that form entire 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 copper, iron, aluminum, silver, gold, chromium, manganese, nickel, zinc, lead and many others.
For all metals, common physical properties can be identified, which are explained by the formation of a metallic bond. What are these properties?
- Malleability and ductility. It is known that many metals can be rolled even to the state of foil (gold, aluminum). Others produce wire, flexible metal sheets, and products that can be deformed during physical impact, but immediately restore their shape after it stops. It is these qualities of metals that are called malleability and ductility. The reason for this feature is the metal type of connection. The ions and electrons in the crystal slide relative to each other without breaking, which allows maintaining the integrity of the entire structure.
- Metallic shine. It also explains the metallic bond, the formation mechanism, its characteristics and features. Thus, not all particles are able to absorb or reflect light waves of the same wavelength. The atoms of most metals reflect short-wave rays and acquire almost the same color of silver, white, and pale bluish tint. The exceptions are copper and gold, their colors are red-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 the metallic type of bond is realized in its formation. Due to the “electron gas” moving inside the crystal, electric current and heat are instantly and evenly distributed between all atoms and ions and are conducted through the metal.
- Solid state of aggregation under normal conditions. The only exception here is mercury. All other metals are necessarily strong, solid compounds, as well as their alloys. This is also a result of metallic bonding being present in metals. The mechanism of formation of this type of particle binding fully confirms the properties.
These are the main physical characteristics of metals, which are explained and determined precisely by the scheme of formation of a metallic bond. This method of connecting atoms is relevant specifically for metal elements and their alloys. That is, for them in solid and liquid states.
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 slightly different natures and distinctive features of the particles being bonded.
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 outer unpaired electrons from the nucleus. At the same time, the atom has a lot of free orbitals. The diagram of the formation of a metallic bond will precisely 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 through different parts of the lattice. Periodically, each of them attaches to an ion at a site in the crystal and turns it into an atom, then detaches again to form an ion.
Thus, a metallic bond is the bond between atoms, ions and free electrons in a common metal crystal. An electron cloud moving freely within a structure is called an “electron gas.” This is what explains most metals and their alloys.
How exactly does a metal chemical bond realize itself? Various examples can be given. Let's try to look at it on a piece of lithium. Even if you take it the size of a pea, there will be thousands of atoms. So let’s imagine that each of these thousands of atoms gives up its single valence electron to the common crystalline space. At the same time, knowing the electronic structure of a given element, you 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 metal bond is always strong. After all, electron gas does not allow the crystal to collapse, but only displaces the layers and immediately restores them. It shines, has a certain density (usually high), fusibility, malleability and plasticity.
Where else is metal bonding sold? Examples of substances:
- metals in the form of simple structures;
- all metal alloys with each other;
- all metals and their alloys in liquid and solid states.
There are simply an incredible number of specific examples, since there are more than 80 metals in the periodic table!
Metal bond: mechanism of formation
If we consider it in general terms, we have already outlined the main points above. The presence of free electrons and electrons that are easily detached from the nucleus due to low ionization energy are the main conditions for the formation of this type of bond. Thus, it turns out that it is realized between the following particles:
- atoms at the sites of the crystal lattice;
- free electrons that were valence electrons in the metal;
- ions at the sites of the crystal lattice.
The result is a metal bond. The mechanism of formation is generally expressed by the following notation: Me 0 - e - ↔ Me n+. From the diagram it is obvious what particles are present in the metal crystal.
The crystals themselves can have different shapes. 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 in the crystal nodes. The lattices themselves can have different geometric shapes in space.
- Body-centric cubic lattice - alkali metals.
- Hexagonal compact structure - all alkaline earths except barium.
- Face-centric cubic - aluminum, copper, zinc, many transition metals.
- Mercury has a rhombohedral structure.
- Tetragonal - indium.
The lower and lower it is located in the periodic system, the more complex its packaging and 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 the crystal. Alloys have very diverse organizations in space, some of which have not yet been fully studied.
Communication characteristics: non-directional
Covalent and metallic bonds have one very pronounced distinctive 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 boundaries in different directions, each electron is capable of attaching to absolutely any ion at the nodes of the structure. That is, interaction is carried out in different directions. Hence they say that the metallic bond is non-directional.
The mechanism of covalent bonding involves the formation of shared 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. Thus, covalent and metallic bonds are again opposites according to this indicator.
The first is saturable. The atoms taking part in its formation have a strictly defined number of valence external electrons, which are directly involved in the formation of the compound. It will not have more electrons than it has. 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 contrary, are unsaturated. This is due to the presence of numerous free electrons and orbitals inside the crystal. Ions also play a role at the sites of the crystal lattice, each of which can become an atom and again an ion at any time.
Another characteristic of metallic bonding is the delocalization of the internal electron cloud. It manifests itself in the ability of a small number of shared electrons to bind together many atomic nuclei of metals. That is, the density is, as it were, delocalized, distributed evenly between all parts 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:
- zinc;
- aluminum;
- potassium;
- chromium.
Formation of a metallic bond between zinc atoms: Zn 0 - 2e - ↔ Zn 2+. The zinc atom has four energy levels. Based on the electronic structure, it has 15 free orbitals - 3 in p-orbitals, 5 in 4 d and 7 in 4f. The electronic structure is as follows: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 0 4d 0 4f 0, a total of 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 for every atom. The result is a huge common space consisting of empty orbitals and a small number of electrons that bind the entire structure together.
Metallic bond between aluminum atoms: AL 0 - e - ↔ AL 3+. The thirteen electrons of an aluminum atom are located at three energy levels, which they clearly have in abundance. 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.
Chrome metal bond. This element is special in its electronic structure. Indeed, to stabilize the system, the electron falls from the 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 electrons. They are the ones who go into the common electronic space to form a chemical bond. There are 15 free orbitals, which is still much more than 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 that reacts even with ordinary water with fire is potassium. What explains these properties? Again, in many ways - by a metal type of connection. This element has only 19 electrons, but they are located at 4 energy levels. That is, in 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 . Only two with very low ionization energy. They break away freely and go into the common electronic space. There are 22 orbitals for movement per atom, that is, a very large free space for “electron gas”.
Similarities and differences with other types of connections
In general, this issue has already been discussed above. One can only generalize and draw a conclusion. The main features of metal crystals that distinguish them from all other types of connections are:
- several types of particles taking part in the binding process (atoms, ions or atom-ions, electrons);
- different spatial geometric structures of crystals.
Metallic bonds have in common with hydrogen and ionic bonds unsaturation and non-directionality. With covalent polar - strong electrostatic attraction between particles. Separately from ionic - a type of particles at the nodes of a crystal lattice (ions). With covalent nonpolar - atoms in the nodes of the crystal.
Types of bonds in metals of different states of aggregation
As we noted above, a 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 is in metal vapors? Answer: covalent polar and non-polar. As with all compounds that are in the form of a gas. That is, when the metal is heated for a long time and transferred from a solid to a liquid state, the bonds do not break and the crystalline structure is preserved. However, when it comes to transferring the liquid into a vapor state, the crystal is destroyed and the metallic bond is converted into a covalent one.
Atoms of most elements do not exist separately, as they can interact with each other. This interaction produces more complex particles.
The nature of a chemical bond is the action of electrostatic forces, which are the forces of interaction between electric charges. Electrons and atomic nuclei have such charges.
Electrons located on the outer electronic levels (valence electrons), being farthest from the nucleus, interact with it weakest, and therefore are able to break away from the nucleus. They are responsible for bonding atoms to each other.
Types of interactions in chemistry
Types of chemical bonds can be presented in the following table:
Characteristics of ionic bonding
Chemical reaction that occurs due to ion attraction having different charges is called ionic. This happens if the atoms being bonded have a significant difference in electronegativity (that is, the ability to attract electrons) and the electron pair goes to the more electronegative element. The result of this transfer of electrons from one atom to another is the formation of charged particles - ions. An attraction arises between them.
They have the lowest electronegativity indices typical metals, and the largest are typical non-metals. Ions are thus formed by the interaction between typical metals and typical nonmetals.
Metal atoms become positively charged ions (cations), donating electrons to their outer electron levels, and nonmetals accept electrons, thus turning into negatively charged ions (anions).
Atoms move into a more stable energy state, completing their electronic configurations.
The ionic bond is non-directional and non-saturable, since the electrostatic interaction occurs in all directions; accordingly, the ion can attract ions of the opposite sign in all directions.
The arrangement of the ions is such that around each there is a certain number of oppositely charged ions. The concept of "molecule" for ionic compounds doesn't make sense.
Examples of education
The formation of a bond in sodium chloride (nacl) is due to the transfer of an electron from the Na atom to the Cl atom to form the corresponding ions:
Na 0 - 1 e = Na + (cation)
Cl 0 + 1 e = Cl - (anion)
In sodium chloride, there are six chloride anions around the sodium cations, and six sodium ions around each chloride ion.
When interaction is formed between atoms in barium sulfide, the following processes occur:
Ba 0 - 2 e = Ba 2+
S 0 + 2 e = S 2-
Ba donates its two electrons to sulfur, resulting in the formation of sulfur anions S 2- and barium cations Ba 2+.
Metal chemical bond
The number of electrons in the outer energy levels of metals is small; they are easily separated from the nucleus. As a result of this detachment, metal ions and free electrons are formed. These electrons are called "electron gas". Electrons move freely throughout the volume of the metal and are constantly bound and separated from atoms.
The structure of the metal substance is as follows: the crystal lattice is the skeleton of the substance, and between its nodes electrons can move freely.
The following examples can be given:
Mg - 2e<->Mg 2+
Cs-e<->Cs+
Ca - 2e<->Ca2+
Fe-3e<->Fe 3+
Covalent: polar and non-polar
The most common type of chemical interaction is a covalent bond. The electronegativity values of the elements that interact do not differ sharply; therefore, only a shift of the common electron pair to a more electronegative atom occurs.
Covalent interactions can be formed by an exchange mechanism or a donor-acceptor mechanism.
The exchange mechanism is realized if each of the atoms has unpaired electrons on the outer electronic levels and the overlap of atomic orbitals leads to the appearance of a pair of electrons that already belongs to both atoms. When one of the atoms has a pair of electrons on the outer electronic level, and the other has a free orbital, then when the atomic orbitals overlap, the electron pair is shared and interacts according to the donor-acceptor mechanism.
Covalent ones are divided by multiplicity into:
- simple or single;
- double;
- triples.
Double ones ensure the sharing of two pairs of electrons at once, and triple ones - three.
According to the distribution of electron density (polarity) between bonded atoms, a covalent bond is divided into:
- non-polar;
- polar.
A nonpolar bond is formed by identical atoms, and a polar bond is formed by different electronegativity.
The interaction of atoms with similar electronegativity is called a nonpolar bond. The common pair of electrons in such a molecule is not attracted to either atom, but belongs equally to both.
The interaction of elements differing in electronegativity leads to the formation of polar bonds. In this type of interaction, shared electron pairs are attracted to the more electronegative element, but are not completely transferred to it (that is, the formation of ions does not occur). As a result of this shift in electron density, partial charges appear on the atoms: the more electronegative one has a negative charge, and the less electronegative one has a positive charge.
Properties and characteristics of covalency
Main characteristics of a covalent bond:
- The length is determined by the distance between the nuclei of interacting atoms.
- Polarity is determined by the displacement of the electron cloud towards one of the atoms.
- Directionality is the property of forming bonds oriented in space and, accordingly, molecules having certain geometric shapes.
- Saturation is determined by the ability to form a limited number of bonds.
- Polarizability is determined by the ability to change polarity under the influence of an external electric field.
- The energy required to break a bond determines its strength.
An example of a covalent non-polar interaction can be the molecules of hydrogen (H2), chlorine (Cl2), oxygen (O2), nitrogen (N2) and many others.
H· + ·H → H-H molecule has a single non-polar bond,
O: + :O → O=O molecule has a double nonpolar,
Ṅ: + Ṅ: → N≡N the molecule is triple nonpolar.
Examples of covalent bonds of chemical elements include molecules of carbon dioxide (CO2) and carbon monoxide (CO), hydrogen sulfide (H2S), hydrochloric acid (HCL), water (H2O), methane (CH4), sulfur oxide (SO2) and many others .
In the CO2 molecule, the relationship between carbon and oxygen atoms is covalent polar, since the more electronegative hydrogen attracts electron density. Oxygen has two unpaired electrons in its outer shell, while carbon can provide four valence electrons to form the interaction. As a result, double bonds are formed and the molecule looks like this: O=C=O.
In order to determine the type of bond in a particular molecule, it is enough to consider its constituent atoms. Simple metal substances form a metallic bond, metals with nonmetals form an ionic bond, simple nonmetal substances form a covalent nonpolar bond, and molecules consisting of different nonmetals form through a polar covalent bond.
It is extremely rare that chemical substances consist of individual, unrelated atoms of chemical elements. Under normal conditions, only a small number of gases called noble gases have this structure: helium, neon, argon, krypton, xenon and radon. Most often, chemical substances do not consist of isolated atoms, but of their combinations into various groups. Such associations of atoms can number a few, hundreds, thousands, or even more atoms. The force that holds these atoms in such groups is called chemical bond.
In other words, we can say that a chemical bond is an interaction that provides the connection of individual atoms into more complex structures (molecules, ions, radicals, crystals, etc.).
The reason for the formation of a chemical bond is that the energy of more complex structures is less than the total energy of the individual atoms that form it.
So, in particular, if the interaction of atoms X and Y produces a molecule XY, this means that the internal energy of the molecules of this substance is lower than the internal energy of the individual atoms from which it was formed:
E(XY)< E(X) + E(Y)
For this reason, when chemical bonds are formed between individual atoms, energy is released.
Electrons of the outer electron layer with the lowest binding energy with the nucleus, called valence. For example, in boron these are electrons of the 2nd energy level - 2 electrons per 2 s- orbitals and 1 by 2 p-orbitals:
When a chemical bond is formed, each atom tends to obtain the electronic configuration of noble gas atoms, i.e. so that there are 8 electrons in its outer electron layer (2 for elements of the first period). This phenomenon is called the octet rule.
It is possible for atoms to achieve the electron configuration of a noble gas if initially single atoms share some of their valence electrons with other atoms. In this case, common electron pairs are formed.
Depending on the degree of electron sharing, covalent, ionic and metallic bonds can be distinguished.
Covalent bond
Covalent bonds most often occur between atoms of nonmetal elements. If the nonmetal atoms forming a covalent bond belong to different chemical elements, such a bond is called a polar covalent bond. The reason for this name lies in the fact that atoms of different elements also have different abilities to attract a common electron pair. Obviously, this leads to a displacement of the common electron pair towards one of the atoms, as a result of which a partial negative charge is formed on it. In turn, a partial positive charge is formed on the other atom. For example, in a hydrogen chloride molecule the electron pair is shifted from the hydrogen atom to the chlorine atom:
Examples of substances with polar covalent bonds:
CCl 4, H 2 S, CO 2, NH 3, SiO 2, etc.
A covalent nonpolar bond is formed between nonmetal atoms of the same chemical element. Since the atoms are identical, their ability to attract shared electrons is also the same. In this regard, no displacement of the electron pair is observed:
The above mechanism for the formation of a covalent bond, when both atoms provide electrons to form common electron pairs, is called exchange.
There is also a donor-acceptor mechanism.
When a covalent bond is formed by the donor-acceptor mechanism, a shared electron pair is formed due to the filled orbital of one atom (with two electrons) and the empty orbital of another atom. An atom that provides a lone pair of electrons is called a donor, and an atom with a vacant orbital is called an acceptor. Atoms that have paired electrons, for example N, O, P, S, act as donors of electron pairs.
For example, according to the donor-acceptor mechanism, the fourth covalent N-H bond is formed in the ammonium cation NH 4 +:
In addition to polarity, covalent bonds are also characterized by energy. Bond energy is the minimum energy required to break a bond between atoms.
The binding energy decreases with increasing radii of bonded atoms. Since we know that atomic radii increase down the subgroups, we can, for example, conclude that the strength of the halogen-hydrogen bond increases in the series:
HI< HBr < HCl < HF
Also, the bond energy depends on its multiplicity - the greater the bond multiplicity, the greater its energy. Bond multiplicity refers to the number of shared electron pairs between two atoms.
Ionic bond
An ionic bond can be considered as an extreme case of a polar covalent bond. If in a covalent-polar bond the common electron pair is partially shifted to one of the pair of atoms, then in an ionic bond it is almost completely “given” to one of the atoms. The atom that donates electron(s) acquires a positive charge and becomes cation, and the atom that has taken electrons from it acquires a negative charge and becomes anion.
Thus, an ionic bond is a bond formed by the electrostatic attraction of cations to anions.
The formation of this type of bond is typical during the interaction of atoms of typical metals and typical non-metals.
For example, potassium fluoride. The potassium cation is formed by the removal of one electron from a neutral atom, and the fluorine ion is formed by the addition of one electron to the fluorine atom:
An electrostatic attraction force arises between the resulting ions, resulting in the formation of an ionic compound.
When a chemical bond was formed, electrons from the sodium atom passed to the chlorine atom and oppositely charged ions were formed, which have a completed external energy level.
It has been established that electrons from the metal atom are not completely detached, but are only shifted towards the chlorine atom, as in a covalent bond.
Most binary compounds that contain metal atoms are ionic. For example, oxides, halides, sulfides, nitrides.
Ionic bonding also occurs between simple cations and simple anions (F −, Cl −, S 2-), as well as between simple cations and complex anions (NO 3 −, SO 4 2-, PO 4 3-, OH −). Therefore, ionic compounds include salts and bases (Na 2 SO 4, Cu(NO 3) 2, (NH 4) 2 SO 4), Ca(OH) 2, NaOH).
Metal connection
This type of bond is formed in metals.
Atoms of all metals have electrons in their outer electron layer that have a low binding energy with the nucleus of the atom. For most metals, the process of losing outer electrons is energetically favorable.
Due to such a weak interaction with the nucleus, these electrons in metals are very mobile and the following process continuously occurs in each metal crystal:
M 0 - ne - = M n + , where M 0 is a neutral metal atom, and M n + is a cation of the same metal. The figure below provides an illustration of the processes taking place.
That is, electrons “rush” across a metal crystal, detaching from one metal atom, forming a cation from it, joining another cation, forming a neutral atom. This phenomenon was called “electron wind,” and the collection of free electrons in a crystal of a nonmetal atom was called “electron gas.” This type of interaction between metal atoms is called a metallic bond.
Hydrogen bond
If a hydrogen atom in a substance is bonded to an element with high electronegativity (nitrogen, oxygen, or fluorine), that substance is characterized by a phenomenon called hydrogen bonding.
Since a hydrogen atom is bonded to an electronegative atom, a partial positive charge is formed on the hydrogen atom, and a partial negative charge is formed on the atom of the electronegative element. In this regard, electrostatic attraction becomes possible between a partially positively charged hydrogen atom of one molecule and an electronegative atom of another. For example, hydrogen bonding is observed for water molecules:
It is the hydrogen bond that explains the abnormally high melting point of water. In addition to water, strong hydrogen bonds are also formed in substances such as hydrogen fluoride, ammonia, oxygen-containing acids, phenols, alcohols, and amines.
A metallic bond is formed between atoms in a metal crystal, resulting from the overlap of valence electrons. So, what is this type of connection, and in what compounds is it present?
What is a metal bond?
A metal chemical bond exists in a metal crystal and in a liquid molten state. It is formed by elements whose atoms at the outer level have few electrons (1-3) compared to the total number of external, energetically close orbitals.
Rice. 1. Scheme of metal bond formation.
Due to their low ionization energy, valence electrons are weakly retained in the atom. Thus, the sodium atom has 9 free and energetically close orbitals per one valence electron (3S 1) (one 3s, three 3p and five 3d).
Due to the low value of the ionization energy, the valence electron is weakly held and moves freely not only within its 9 free orbitals, but when tightly packed in the crystal and in the free orbitals of other atoms, making a connection.
The chemical bond is highly delocalized: electrons are shared (“electron gas”) and move throughout the piece of metal, which is generally electrically neutral, between positively charged ions.
The free movement of electrons throughout the crystal explains the non-directionality and unsaturation of the bond, as well as such physical properties of metals as plasticity, luster, electrical and thermal conductivity.
Rice. 2. Properties of metallic chemical bonds.
Characteristic crystal lattices
Metals almost always form highly symmetrical lattices with atoms closely packed together. There are three types of crystal lattices:
