Types of chemical bonds. How to connect atoms?
Chemistry is an amazing and, I confess, complicated science. For some reason, it is associated with bright experiments, multi-colored test tubes, thick clouds of steam. But few people think about where this “magic” comes from. In fact, no reaction takes place without the formation of compounds between the atoms of the reactants. Moreover, these "jumpers" are sometimes found in simple elements. They affect the ability of substances to react and explain some of their physical properties.
What kinds of chemical bonds are there and how do they affect compounds?
We must begin with the simplest. A chemical bond is an interaction in which the atoms of substances combine to form more complex substances. It is erroneous to believe that this is characteristic only of compounds like salts, acids and bases - even simple substances whose molecules consist of two atoms have these “bridges”, if so you can conditionally call a bond.By the way, it is important to remember that only atoms with different charges can unite (these are the fundamentals of physics: the equally charged particles repel, and the opposite ones attract), so that in complex substances there is always a cation (ion with a positive charge) and an anion (negative particle) and the connection itself will always be neutral.
Now we will try to understand how the formation of a chemical bond occurs.
Any substance has a certain number of electrons distributed in energy layers. The outermost layer, on which the smallest amount of these particles is usually located, is considered the most vulnerable. You can find out their number by looking at the group number (a line with numbers from one to eight at the top of the periodic table) in which the chemical element is located, and the number of energy layers is equal to the period number (from one to seven, the vertical line to the left of the elements).
Ideally, there are eight electrons in the outer energy layer. If they are not enough, the atom tries to drag them from another particle. It is during the selection process of electrons required for the completion of the outer energy layer that chemical bonds are formed.Their number can vary and depends on the number of valence, or unpaired, particles (to find out how many there are in an atom, you need to make up its electronic formula). The number of electrons that do not have a pair will be equal to the number of bonds formed.
A little more about types
The types of chemical bonds formed during reactions or simply in a molecule of a substance entirely depend on the element itself. There are three types of “jumpers” between atoms: ionic, metallic and covalent. The latter, in turn, is divided into polar and non-polar.
In order to understand what kind of bond atoms are connected with, they use a kind of rule: if the elements are in the right and left parts of the table (that is, they are metal and non-metal, for example, NaCl), then their combination is an excellent example of ionic bond. Two non-metals form a covalent polar bond (HCl), and two atoms of one substance, combining into one molecule, form a covalent non-polar (Cl2, O2). The above types of chemical bonds are not suitable for substances consisting of metals - there is only a metal bond.
As mentioned earlier, types of chemical bonds have a certain effect on substances. So, for example, the covalent “bridge” is very unstable, which is why connections with it are easily destroyed with the slightest external influence, for example, heating. However, it concerns only molecular substances. Those that have a non-molecular structure are practically indestructible (a perfect example is a diamond crystal - a combination of carbon atoms).
Let us return to the polar and non-polar covalent bonds. With the non-polar, everything is simple - the electrons between which a “bridge” is formed are at equal distance from the atoms. But in the second case, they are shifted to one of the elements. The winner in the "overtightening" will be the substance whose electronegativity (the ability to attract electrons) is higher. It is determined by special tables, and the greater the difference of this magnitude between the two elements, the more polar will be the connection between them. True, the only thing for which knowledge of the electronegativity of elements can be useful is the definition of a cation (a positive charge - a substance that has this quantity less) and an anion (a negative particle with a better ability to attract electrons).
Not all types of chemical bonds are suitable for the combination of metal and non-metal. As mentioned above, if the difference in electronegativity of the elements is huge (and this is what happens when they are located in opposite parts of the table), an ionic bond is formed between them. In this case, the valence electrons transfer from an atom with a lower electronegativity to an atom with a larger one, forming an anion and a cation. The most striking example of such a bond is a compound of a halogen and a metal, for example AlCl2or HF.
With metals is still easier. They are alien to the above types of chemical bonds, because they have their own. It can combine as atoms of one substance (Li2) and different (AlCr2), in the latter case, alloys are formed. If we talk about physical properties, then metals combine in themselves plasticity and strength, that is, they do not collapse at the slightest impact, but simply change the shape.
By the way, chemical bonds in molecules also exist. They are called intermolecular. The most common type is hydrogen bonding, in which a hydrogen atom borrows electrons from an element with a high electronegativity (from a water molecule, for example).