All currently known chemical elements located in the periodic table are conventionally divided into two large groups: metals and non-metals. In order for them to become not just elements, but compounds, chemicals, could interact with each other, they must exist in the form of simple and complex substances.
For this, some electrons try to accept, while others give. Replenishing each other in this way, the elements form various chemical molecules. But what allows them to stay 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. In its formation, valence unpaired particles take part. Examples: halogens, oxygen, hydrogen, nitrogen, sulfur, phosphorus.
- Covalent polar. Formed between two different non-metals or between a very weak metal in properties and a weak in electronegativity non-metal. It is also based on common electron pairs and their pulling toward themselves 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, is formed between the strongly electronegative atom of one molecule and the positive of another. Most often this happens when substances are dissolved in water (alcohol, ammonia, and so on). Due to this connection, macromolecules of proteins, nucleic acids, complex carbohydrates and so on can exist.
- Ion bond. It is formed due to the forces of electrostatic attraction of uncharged metal ions and nonmetals. 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 metal bond, the formation mechanism of which, as well as properties, will be considered 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 each chemical bond as a reference. They are only conventional units. After all, the basis of all interactions is a single principle - the electron-static interaction. Therefore, the ionic, metallic, covalent bond and hydrogen bond have a single chemical nature and are only boundary cases of each other.
Metals and their physical properties
Metals are in the vast majority of all chemical elements. This is due to their special properties. A significant part of them was obtained by human nuclear reactions in the laboratory, they are radioactive with a short half-life.
However, most are natural elements that form whole rocks and ores, 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, general physical properties can be distinguished, which are explained by the metal bond formation scheme. What are these properties?
- Durability and ductility. It is known that many metals can be rolled even to the state of foil (gold, aluminum). From others, wire, metal flexible sheets, and products capable of deforming under physical influence, but immediately restore shape after stopping it, are obtained. It is these qualities of metals that are called malleability and ductility. The reason for this feature is the metallic type of bond. Ions and electrons in the crystal slip relative to each other without breaking, which allows you to maintain the integrity of the entire structure.
- Metallic shine. This also explains the metal bond, the mechanism of formation, its characteristics and features. So, not all particles are capable of absorbing or reflecting light waves of the same length. The atoms of most metals reflect short-wave rays and acquire almost the same color as a silver, white, pale bluish hue. Exceptions are copper and gold, their color is red-red and yellow, respectively. They are able to reflect longer wavelength radiation.
- Heat 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, the electric current and heat are instantly and evenly distributed between all atoms and ions and passed through the metal.
- Solid state under normal conditions. The only exception is mercury. All other metals are necessarily strong, solid compounds, as well as their alloys. This is also the result of the presence of a metal bond in metals. The mechanism of formation of this type of particle binding fully confirms the properties.
These are the basic physical characteristics for metals, which are explained and determined precisely by the metal bond formation scheme. Such a method of joining atoms is relevant precisely for elements of metals, their alloys. That is, for them in solid and liquid state.
Metallic type of chemical bond
What is its feature? The fact is that such a bond is not formed due to uncharged 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 bound particles.
All metals have such characteristics as:
- a small number of electrons at the external energy level (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 nucleus. At the same time, there are a lot of free orbitals at the atom. The metal bond formation scheme 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 from each atom are fed into it, which begin to wander freely around different parts of the lattice. Periodically, each of them joins the ion in the node of the crystal and turns it into an atom, then detaches again, forming an ion.
Thus, a metal bond is a bond between atoms, ions and free electrons in a common metal crystal. An electron cloud freely moving inside a structure is called an “electron gas." It is he who explains most of the physical properties of metals and their alloys.
How exactly does a metal chemical bond realize itself? There are various examples. Let's try to consider 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 its valence single electron to the common crystalline space. Moreover, knowing the electronic structure of this 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 metal-bonded substance is always durable. After all, the electron gas does not allow the crystal to crumble, but only shifts the layers and immediately restores. It shines, has a certain density (most often high), fusibility, ductility and ductility.
Where else is metal bond 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 state.
Concrete examples can be given just an incredible amount, because there are more than 80 metals in the periodic system!
Metal bond: formation mechanism
If we consider it in a general form, then we have already outlined the main points above. The presence of free atomic orbitals and electrons that are 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 realized between the following particles:
- atoms in the nodes of the crystal lattice;
- free electrons that were metal valence;
- ions in the nodes of the crystal lattice.
The result is a metal bond. The formation mechanism in general is expressed by the following notation: Me 0 - e - ↔ Me n + . From the diagram it is obvious which particles are present in the metal crystal.
The crystals themselves can have a different shape. It depends on the specific substance we are dealing with.
Types of Metal Crystals
This structure of the metal or its alloy is characterized by a very dense packing of particles. It is provided by ions in the nodes of the crystal. The lattices themselves can be of different geometric shapes in space.
- Volume-centric cubic lattice - alkali metals.
- The hexagonal compact structure is all alkaline earth except barium.
- Face-centric cubic - aluminum, copper, zinc, many transition metals.
- The rhombohedral structure is in mercury.
- Tetragonal - indium.
The heavier the metal and the lower it is located in the periodic system, the more complicated its packing and spatial organization of the crystal. In this case, a metal chemical bond, examples of which can be given for each existing metal, is crucial in the construction of the crystal. Alloys have very diverse organizations in space, some of them are still not fully understood.
Communication characteristics: omnidirectionality
Covalent and metallic bonds have one very distinctive distinguishing feature. Unlike the first, the metal bond is not directional. What does it mean? That is, the electron cloud inside the crystal moves completely freely within it in different directions, each of the electrons is able to attach to absolutely any ion in the nodes of the structure. That is, the interaction is carried out in different directions. Hence they say that the metal bond is non-directional.
The covalent bonding mechanism involves 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, covalent and metal bonds in this indicator are again opposites.
The first is saturated. The atoms involved in its formation have a strictly defined number of valence external electrons that are directly involved in the formation of the compound. More than he has, he will not have electrons. Therefore, the number of formed bonds is limited by valency. Hence the saturation of the bond. Due to this characteristic, most compounds have a constant chemical composition.
Metal and hydrogen bonds, in contrast, are unsaturated. This is due to the presence of numerous free electrons and orbitals inside the crystal. Also the role is played by ions in the nodes of the crystal lattice, each of which can become an atom and again an ion at any time.
Another characteristic of metal bonding is the delocalization of the internal electron cloud. It manifests itself in the ability of a small number of common electrons to bind together many atomic nuclei of metals. That is, the density is delocalized, as it were, distributed evenly between all the links in the crystal.
Examples of bond formation in metals
Consider a few specific options that illustrate how a metal bond is formed. Examples of substances are as follows:
- zinc;
- aluminum;
- potassium;
- chromium.
The formation of a metal bond between zinc atoms: Zn 0 - 2e - ↔ Zn 2+ . The zinc atom has four energy levels. Based on the electronic structure, there are 15–3 free orbitals on p-orbitals, 5 on 4 d and 7 on 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 , 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 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.
Metallic bond between aluminum atoms: AL 0 - e - ↔ AL 3+ . Thirteen electrons of an aluminum atom are located at three energy levels, which they clearly 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.
Chrome metal bond. This element is special in its electronic structure. Indeed, to stabilize the system, an electron fails 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 . Only 24 electrons, of which six are valence. It is they who go into the common electronic space for the formation of a chemical bond. There are 15 free orbitals, which is still much more than is required for filling. Therefore, chromium is also a typical example of a metal with a corresponding bond in the molecule.
One of the most active metals that react even with ordinary water with fire is potassium. What explains these properties? Again, in many ways, with the metallic type of connection. There are only 19 electrons in this element, but they are already 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 valence electrons, with a very low ionization energy. Freely come off and go into the general electronic space. There are 22 pieces of orbitals to move one atom, that is, a very vast free space for "electron gas".
Similarities and differences with other types of relationships
In general, this issue has already been considered above. You can only generalize and conclude. The main distinguishing features of metal bonds from all other types of bonds 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, metal is combined by unsaturation and non-directivity. With covalent polar - strong electrostatic attraction between particles. Separately with the ionic type of particles in the nodes of the crystal lattice (ions). With covalent non-polar - atoms in the nodes of the crystal.
Types of bonds in metals of different state of aggregation
As we noted above, a metallic chemical bond, examples of which are given in the article, is formed in two aggregate states 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 with all compounds in the form of gas. That is, with prolonged heating of the metal and its transfer from a solid state to a liquid, bonds do not break and the crystal structure is preserved. However, when it comes to transferring a liquid to a vapor state, the crystal is destroyed and the metal bond is converted to covalent.