For convenience of record of the chemical composition and structure of chemical certain rules of drawing up chemical formulas by means of special symbols designations, numbers and auxiliary signs were created.
1. Chemical formulas participate in writing of the equations of chemical reactions, the schematical image of chemical processes, communications. For their writing the so-called language of chemistry which represents a set of symbols, such as symbols of chemical elements, amount of atoms of each element in the described substance and so forth is used.
2. Symbols of chemical elements – one or several letters of the Latin alphabet, from which the first capital letter. It is schematical record of full naming of an element, for example, Ca - it is calcium or lat. Calcium.
3. The amount of atoms is expressed by mathematical numbers, for example, H_2 - it is two atoms of hydrogen.
4. There are several ways of record of a chemical formula: the elementary, empirical, rational and structural. The simplest formula of record reflects a ratio of chemical elements with the indication of atomic mass which is specified after the sign of chemical element in the form of the lower index. For example, H_2O is the simplest formula of a molecule of water, i.e. two atoms of hydrogen and one atom of oxygen.
5. The empirical chemical formula differs from the elementary in the fact that reflects composition of substance, but not structure of molecules. The formula shows amount of atoms in one molecule which is also represented in the form of the lower index.
6. The difference between the simplest and empirical formulas shows record of a formula of benzene: CH and C_6H_6 respectively. I.e. the simplest formula shows a direct ratio of atoms of carbon and hydrogen while empirical says that the molecule of substance contains 6 atoms of carbon and 6 – hydrogen.
7. The rational formula accurately shows presence of groups of atoms of elements in connection. Such groups are allocated with parentheses, and their quantity is specified by the lower index after brackets. In a formula also square brackets in which complex compounds of atoms (connections with neutrally loaded molecule, an ion) consist are used.
8. The structural formula is represented graphically in two- or three-dimensional space. Chemical bonds between atoms are represented in the form of lines, at the same time atoms are specified so many time how many they participate in connection. Most visually the formula of substance is expressed by the three-dimensional image which show a relative positioning of atoms and distance between them.