Oxygen valency in compounds

In order to determine the possible values ​​​​of the valence of oxygen, one should study the position of the element in the periodic table, the main features of the structure of its atom. This approach is convenient when studying the question of which valency oxygen has is typical and which is uncharacteristic for it. In the most common compounds, the usual valency - II is manifested. This feature allows you to determine the number of bonds of another atom in ready-made binary formulas with the participation of oxygen. Also find out how many valence electrons does neon have

What is the valency of oxygen?

At the initial stage of accumulation of knowledge about the properties and  structure of substances chemists thought that valency is the ability to bind a certain number of atoms into a molecule of a substance. Many scientists after the discovery of the element tried to understand what valence oxygen has. The answer was obtained experimentally: oxygen adds two monovalent hydrogen atoms in a chemical reaction, which means it is bivalent. Ideas about the chemical bond changed with the accumulation of knowledge about the structure of matter. In their theory of valency, G. Lewis and W. Kossel reveal the essence of chemical interaction from the point of view of the electronic structure. The researchers explained the ability of an atom to form a certain number of bonds by striving for the most stable energy state. If it is reached, the smallest particle of matter becomes more stable.

Features of the placement of oxygen in the periodic table

In order to determine what valence oxygen has, it is necessary to consider some features of its  electronic structure.  Oxygen heads the 16th group of the periodic table. The trivial name of the family of elements is "chalcogens", according to the outdated classification, they belong to the VI (A) group. In the periodic table, oxygen is in cell number 8. The nucleus contains in its composition 8 positive and the same number of neutral elementary particles. In the space of an atom, there are two  energy levels  that arise when 8 electrons move, of which 6 are external.

What is the relationship between the composition of an atom and valency?

The last level of the oxygen atom contains 2 unpaired electrons. The element is inferior to fluorine in terms of electronegativity (the ability to attract binding electron pairs to itself). When compounds are formed with other elements, oxygen attracts the total electron density that has arisen in the molecule (except for fluorine electrons). Achieving a stable state of the outer shell is possible by adding two negative charges. This means that oxygen needs 2 electrons. The following options are possible: accept one electron (valence II), take away 2 electrons from another atom (valency II), do not accept electrons from other atoms (valence 0). The typical behavior of oxygen characterizes the second case. You can use this method to find out what is the most typical valency of oxygen in its common compounds. These include most oxides of metals and nonmetals.

How does valence manifest itself in compounds?

Oxygen is able to directly interact with many chemical elements. Its compounds are known with almost all representatives of the periodic table (with the exception of inert gases: argon, helium, neon). Oxygen may not directly react with halogens, noble metals, but oxides Au2O3, F2O, Cl2O7 and others exist (obtained indirectly). Binary compounds, in the formation of which oxygen takes part, are characterized by a  covalent bond and polarity. The valency in such molecules depends on the number of pairs of electrons that have arisen, to which the nuclei of different atoms are attracted. In the vast majority of compounds, oxygen atoms are involved in the creation of two covalent bonds. For example, in oxides CO2, P2O5, SO2, SO3, K2O, B2O3, Mo2O5 and other molecules. In the hydroxonium cation H3O+, oxygen exhibits an atypical valency III. The presence of the peroxo group –O–O– is responsible for the unusual nature of hydrogen peroxide H2O2. In this compound, oxygen exhibits its inherent valency II.

How to determine the valency of  elements

The idea of ​​the valence possibilities of oxygen is given by the Lewis structure - the chemical sign of an element, around which dots mark the electrons of the outer layer. It is they who take part in the creation of molecules, are part of common electron pairs. The Lewis formula clearly demonstrates the valence of oxygen, corresponding to the number of its unpaired electrons (2). The same result is obtained by using graphic electronic structures. In two cells  of the external energy level oxygen contains unpaired electrons (indicated by arrows in the formula). Information about the valency of oxygen makes it possible to determine the value for neighboring atoms from the finished formula of a binary compound. To do this, carry out simple calculations. First, the number of O atoms is multiplied by the normal valence for oxygen. The resulting value must be divided by the index that is indicated in the formula next to the chemical symbol of another element in combination with oxygen. Using a simple method, we calculate the valency of carbon and phosphorus in their oxides.

  1. Multiply the index to the lower right of the O sign in CO2 dioxide by the typical valency of the element: 2 • 2 = 4. Divide the resulting number by the index indicated for carbon: 4/1 = 4. In CO2 dioxide, carbon is in its highest valence state IV.

  2. We multiply the index at the bottom right of the chemical symbol of oxygen in P2O5 phosphorus oxide by the typical valency of the O atom: 5 • 2 = 10. We divide this number by the index indicated in the formula to the right below the phosphorus atom: 10/2 = 5. In the oxide, phosphorus is in the state its highest valence V.