It has long been accepted in chemistry to write down the composition of any substance in abbreviated form, using symbols and indices (numbers). Recording in this form is called the "empirical" formula. So, for example, the composition of phosphoric acid is reflected in this form - H3PO4. From this entry it follows that the phosphoric acid molecule consists of three hydrogen atoms, one - phosphorus, and four - oxygen. However, it is not clear how the elements are interconnected, i.e. information is incomplete. To fill this gap, the structural formula of the substance is used.
This connection record is more informative, because with its help, it is schematically shown how and in what sequence the elements of a substance are connected to each other. In this case, each covalent bond (pair of electrons) is represented by a dash and corresponds to one unit of valence.
For example, oxygen has a valence of two, it is surrounded by two dashes, hydrogen has a valence of one, therefore, one dash, phosphorus - five, five dashes. On the basis of suchspelling, you can assume the chemical properties of substances, classify and systematize them.
Structural formula can be written in full and abbreviated form. When written in expanded form, all bonds between atoms are indicated, but when written in abbreviated form, they are not.
The most visual 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 connection. This phenomenon is called "isomerism" (branching of the carbon chain).
So, for example, the structural formula of ethane says that all the valences of carbon are occupied, and it can no longer attach other atoms to itself. From this it can be seen that С2Н6 is a representative of saturated hydrocarbons, the bonds in the molecule are covalent, there are no free electrons, therefore, only reactions are possible for ethane substitution and r
flashing.
The structural formula of the substance also indicates the functional groups of carbohydrates: alkyl group - in alcohols, aldehyde - in aldehydes, benzene nucleus - in aromatic compounds. In addition, with the help of a schematic representation, it is easy to “see” saturated hydrocarbons by the presence of characteristic bonds - 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 carbohydrateIt has the same quantitative and qualitative composition as glucose. In solutions, it comes in several forms at once. From the graphical formula of fructose, it can be seen that it contains ketone and hydroxyl groups, i.e. this substance has the "dual" properties of alcohols and ketones. Also, this formula allows us to establish that this keto alcohol is formed by the residues of cyclic a-glucose and pentose (fructose).
Thus, a structural formula is a graphic representation of a substance, with which you can learn about the arrangement of atoms in a molecule, taking into account the type of bond and their features.
