Valency – one of the main terms used in the theory of the chemical building. This concept defines ability of atom to form chemical bonds and quantitatively represents number of communications in which he participates.
Instruction
1. Valency (Latin of valentia - "force") – an indicator of ability of atom to attach to itself other atoms, forming with them chemical bonds in a molecule. Total number of communications in which atom can participate equals to number of its not coupled electrons. Such communications are called covalent.
2. Not coupled electrons are free electrons of an outer sheath of atom which connect in couples to external electrons of other atom. At the same time each such couple is called electronic, and such electrons – valent. Proceeding from it, determination of valency can sound so: this number of electronic couples on which this atom is connected with other atoms.
3. Valency of atom is schematically represented in structural chemical formulas. If such information is not necessary, then use the simplest formulas in which valency is not specified.
4. The maximum indicator of valency of chemical elements of one group of a periodic system, as a rule, is equal to serial number of group. In various chemical compounds atoms of one element can have different valency. The polarity of the formed covalent communications is not considered therefore valency has no sign. It cannot be either zero, nor negative size.
5. A quantitative measure of any chemical element it is considered to be number of monovalent atoms of hydrogen or bivalent atoms of oxygen. However when determining valency it is possible to use also other elements which valency is precisely known.
6. Sometimes the concept of valency is identified with the concept "oxidation level", however it is incorrect though in certain cases these indicators coincide. Oxidation level – the formal term meaning a possible charge which would receive atom if its electrons in electronic couples passed to more electronegative atoms. At the same time oxidation level is expressed in terms of a charge and can have the sign, unlike valency. This term became widespread in inorganic chemistry as in inorganic compounds it is difficult to judge valency. Valency is used in organic chemistry as the majority of organic compounds has the molecular building.