It has long been accepted in chemistry to write the composition of any substance in abbreviated form, using symbols and indices (numbers). A record in this form is called an “empirical” formula. So, for example, the composition of phosphoric acid is reflected in this form - H 3 PO 4. From this record it follows that the molecule of phosphoric acid consists of three hydrogen atoms, one of phosphorus, and four of oxygen. However, it is not clear how the elements are interconnected, i.e. information is incomplete. To eliminate this gap, the structural formula of the substance is used.
Such a connection record is very informative, because with its help, it is shown schematically how and in what sequence the elements of a substance are interconnected. In addition, each covalent bond (a pair of electrons) is represented by a dash and corresponds to one unit of valency.
For example, oxygen has a valency of two, it is surrounded by two lines, hydrogen is one valence, therefore, one line, phosphorus - five, five lines. Based on this writing, we can assume the chemical properties of substances, classify and systematize them.
The structural formula can be written in full and abbreviated form. When an expanded record is indicated, all the bonds between the atoms are indicated, and when written in an abbreviated form - no.
The most graphic and significant is the graphic representation of compounds in organic chemistry. After all, the properties of substances depend not only on the number of atoms and molecules, but also on the order of their combination. This phenomenon is called "isomerism" (carbon chain branching).
For example, the structural formula of ethane suggests that all valencies of carbon are occupied, and it can no longer attach other atoms to itself. From this it can be seen that C
2 H
6 is a representative of saturated hydrocarbons, the bonds in the molecule are covalent, there are no free electrons, therefore, for ethane, only
substitution reactions and
yelling
The structural formula of the substance also indicates the functional groups of carbohydrates: the alkyl group in alcohols, the aldehyde group in aldehydes, and the benzene core in aromatic compounds. In addition, with the help of a schematic image, it is easy to “see” the presence of characteristic bonds with the limiting hydrocarbons — a single covalent bond. Unsaturated: ethylene - one double bond, diene - two double bonds, triple - acetylene.
The structural formula of fructose is an example of spatial isomerism. This carbohydrate has the same quantitative and qualitative composition as glucose. In solutions comes in several forms at once. It can be seen from the graphic formula of fructose that it contains ketone and hydroxyl groups, i.e. this substance has the "dual" properties of alcohols and ketones. This formula also allows us to establish that this ketoalcohol is formed by residues of cyclic a-glucose and pentose (fructose).
Thus, the structural formula is a graphic image of a substance, with which you can find out about the location of atoms in a molecule, taking into account the type of bond and their features.