What is the degree of oxidation of oxygen? Valence and degree of oxidation of oxygen

We all breathe air, which basically consists of nitrogen and oxygen molecules with little addition of other elements. Thus, oxygen is one of the most important chemical elements. In addition, its molecules exist in a huge number of chemical compounds used in everyday life. To describe all the properties of this element, there are not enough pages and a hundred, so we confine ourselves to the basic facts from history, as well as the basic characteristics of the element-the valence and degree of oxygen oxidation, specific gravity, application, basic physical properties.

The history of the discovery of a chemical element

The official opening date for the chemical element "oxygen" is August 1, 1774. It was on this day that the British chemist J. Priestley completed his experiment on the decomposition of mercury oxide in a sealed vessel. At the conclusion of the experiment, the scientist received a gas that supported combustion. However, this discovery went unnoticed even by the scientist himself. Mr. Priestley thought that he had managed to distinguish not a new element, but an integral part of the air. With his results, Joseph Priestley shared with the famous French scientist and chemist Antoine Lavoisier, who could understand what the Englishman could not do. In 1775, Lavoisier was able to establish that the resulting "constituent part of the air" is in fact an independent chemical element, and called it oxygen, which in Greek means "forming acid". Lavoisier then believed that oxygen is in all acids. Subsequently, formulas were derived for acids that do not contain oxygen atoms, but the name was adopted.

Oxygen - features of the structure of the molecule

This chemical element is a colorless gas that does not smell and taste. The chemical formula is O ₂ . Chemists call ordinary diatomic oxygen either "atmospheric oxygen" or "dioxygen". The molecule of matter consists of two bound oxygen atoms. There are also molecules consisting of three atoms - O ₃ . This substance is called ozone, more details about it will be written below. A molecule with two atoms has a degree of oxidation of oxygen -2, since it contains two unpaired ones capable of forming a covalent bond of an electron. The energy that is released during the decomposition (dissociation) of the oxygen molecule into atoms is 493.57 kJ / mol. This is quite a big value.

Valence and degree of oxidation of oxygen

Under the valence of a chemical element , we mean its ability to attach to itself a certain number of atoms of another chemical element. The valence of an oxygen atom is two. The valency of the oxygen molecule is also equal to two, since two atoms are connected to each other and have the ability to attach to their structure one more atom of another compound, that is, form a covalent bond with it. For example, a water molecule H ₂ O was obtained as a result of the formation of a covalent bond between one oxygen atom and two hydrogen atoms.

Oxygen is found in many of the known chemical compounds. There is even a separate type of chemical compounds - oxides. These are substances obtained by combining almost any chemical element with oxygen. The degree of oxidation of oxygen in oxides is -2. However, in some compounds this indicator may be different. This will be described in more detail below.

Physical properties of oxygen

Normal diatomic oxygen is a gas that does not have color, smell, and taste. In the normal state, its density is 1.42897 kg / m3. The weight of 1 liter of the substance is slightly less than 1.5 grams, that is, in pure form, oxygen is heavier than air. When heated, the molecule dissociates into atoms.

When the temperature of the medium decreases to -189.2 ° C, oxygen changes its structure from gaseous to liquid. At the same time, boiling occurs. When the temperature decreases to -218.35 ° C, the structure changes from liquid to crystalline. At this temperature, oxygen has the form of bluish crystals.

At room temperature, oxygen is weakly soluble in water - one liter of it accounts for 31 milliliters of oxygen. Solubility with other substances: 220 ml per 1 liter of ethanol, 231 ml per 1 liter of acetone.

Chemical properties of oxygen

A whole Talmud can be written about the chemical properties of oxygen. The most important property of oxygen is oxidation. This substance is a very strong oxidant. Oxygen is able to interact with almost all known elements from the periodic table. As a result of this interaction, oxides are formed, as discussed earlier. The degree of oxidation of oxygen in compounds with other elements is basically -2. Examples of such compounds are water (H ₂ O), carbon dioxide (CO ₂ ), calcium oxide, lithium oxide, etc. But there is a certain category of oxides called peroxides or peroxides. Their peculiarity is that in these compounds there is a peroxide group "-O-O-". This group reduces the oxidative properties of O ₂ , so the degree of oxidation of oxygen in the peroxide is -1.

In conjunction with the active alkali metals, oxygen forms superoxides or superexides. An example of such formations is:

• Potassium superoxide (KO ₂ );
• Rubidium superoxide (RbO ₂ ).

Their peculiarity is that the degree of oxidation of oxygen in superoxides is -1/2.

In combination with the most active chemical element - fluorine, fluorides are obtained. About them will be told below.

The highest degree of oxidation of oxygen in compounds

Depending on the substance with which oxygen interacts, there are seven degrees of oxidation of oxygen:

1. -2 in oxides and organic compounds.
2. -1 in peroxides.
3. -1/2 in superoxide.
4. -1/3 - in inorganic ozonides (valid for triatomic oxygen - ozone).
5. +1/2 in the salts of the oxygen cation.
6. +1 in oxygen monofluoride.
7. +2 - in the oxygen difluoride.

As we see, the highest degree of oxidation of oxygen is achieved in oxides and organic compounds, and in fluorides it has even a positive degree. Not all types of interactions can be carried out naturally. Some compounds require special conditions, for example: high pressure, high temperature, exposure to rare compounds that are almost not found in nature. Let's consider the basic connections of oxygen with other chemical elements: oxides, peroxides and fluorides.

Classification of oxides by acid-base properties

There are four types of oxides:

• Basic;
• Acid;
• Neutral;
• Amphoteric.

The degree of oxidation of oxygen in the compounds of these species is -2.

• Basic oxides are compounds with metals that have low degrees of oxidation. Usually, when interacting with acids, the corresponding salt and water are obtained.
• Acid oxides - oxides of nonmetals with a high degree of oxidation. When water is added to them, an acid is formed.
• Neutral oxides are compounds that do not enter into reaction with acids or with bases.
• Amphoteric oxides are compounds with metals that have a low electronegativity. They, depending on the circumstances, exhibit the properties of both acidic and basic oxides.

Peroxides, the degree of oxidation of oxygen in hydrogen peroxide and other compounds

Peroxides are called oxygen compounds with alkali metals. They are obtained by burning these metals in oxygen. Peroxides of organic compounds are extremely explosive. They can also be obtained by absorption with oxides of oxygen. Examples of peroxides:

• Hydrogen peroxide (H ₂ O ₂ );
• Barium peroxide (BaO ₂ );
• Sodium peroxide (Na ₂ O ₂ ).

All of them are united by the fact that they contain the oxygen group -OO-. As a result, the oxygen oxidation in peroxides is -1. One of the most famous compounds with the -OO- group is hydrogen peroxide. Under normal conditions this compound is a pale blue liquid. By its chemical properties, hydrogen peroxide is closer to a weak acid. Since the -OO- bond in the compound is weakly stable, even at room temperature the hydrogen peroxide solution can be decomposed into water and oxygen. It is the strongest oxidizer, however, when interacting with stronger oxidants, the properties of the reducing agent are just hydrogen peroxide. The degree of oxidation of oxygen in hydrogen peroxide, as in other peroxides, is -1.

Other types of peroxides are:

• Superperoxides (superoxides, in which oxygen has an oxidation -1/2);
• Inorganic ozonides (highly unstable compounds having an ozone anion in their structure);
• Organic ozonides (compounds having in their structure a -OOO- bond).

Fluorides, oxygen oxidation in OF2

Fluoride is the most active element of all the currently known. Therefore, the interaction of oxygen with fluorine does not produce oxides, but fluorides. They are named so because in this compound it is not oxygen, but fluorine is an oxidizer. Fluorides can not be obtained naturally. They are only synthesized, obtaining by association of fluorine with an aqueous solution of KOH. Oxygen fluorides are divided into:

• Oxygen difluoride (OF ₂ );
• Oxygen monofluoride (O ₂ F ₂ ).

Let's consider in more detail each of the connections. Oxygen difluoride is a colorless gas with a pronounced unpleasant odor. When cooled, it condenses into a yellowish liquid. In a liquid state, it mixes poorly with water, but it is good with air, fluorine and ozone. According to its chemical properties, oxygen difluoride is a very strong oxidant. The degree of oxidation of oxygen in OF2 is +1, i.e. in this compound, fluorine is an oxidant and oxygen is a reducing agent. OF _{2 is} very toxic, in terms of toxicity exceeds pure fluorine and approaches phosgene. The main use of this compound is as an oxidizing agent for rocket fuel, since oxygen difluoride is not explosive.

Oxygen monofluoride in the normal state is a yellowish solid. When melting, it forms a red liquid. It is the most powerful oxidant, it is extremely explosive when interacting with organic compounds. In this compound, oxygen exhibits oxidation states of +2, i.e., in this fluorine compound, oxygen acts as a reducing agent, and fluorine as an oxidizer.

Ozone and its compounds

Ozone is a molecule that has three oxygen atoms connected to each other. In normal condition, it is a blue gas. When cooled, it forms a deep blue liquid, close to indigo. In solid state it is crystals of dark blue color. Ozone has a sharp odor, in nature it can be felt in the air after a severe thunderstorm.

Ozone, like ordinary oxygen, is a very strong oxidant. By chemical properties, it approaches strong acids. When exposed to oxides, ozone increases their oxidation state with release of oxygen. But at the same time, the degree of oxidation of oxygen decreases. In ozone, chemical bonds are not as strong as in O ₂ , so under normal conditions without applied efforts, it can decompose into oxygen with release of heat energy. When the temperature of the effect on the ozone molecule increases and when the pressure decreases, the process of decomposition into diatomic oxygen with the release of heat is accelerated. In this case, if there is a large ozone content in space, then this process can be accompanied by an explosion.

Since ozone is a very strong oxidant and a large amount of O ₂ is liberated in virtually all processes with its participation, ozone is an extremely toxic substance. However, in the upper layers of the atmosphere, the ozone layer plays the role of a reflector from the ultraviolet radiation of the sun's rays.

From ozone with the help of laboratory instruments create organic and inorganic ozonides. It is very unstable in its structure of matter, so their creation in natural conditions is impossible. Ozonides are stored only at low temperatures, since at normal temperatures they are extremely explosive and toxic.

The use of oxygen and its compounds in industry

Due to the fact that scientists learned at some time what degree of oxidation in oxygen it interacted with other elements, it and its compounds were widely used in industry. Especially after the turboexpanders were invented in the middle of the twentieth century - aggregates capable of converting the potential energy of oxygen into a mechanical one. Since oxygen is an extremely combustible substance, it is used in all industries where fire and heat are necessary. When cutting and welding metals, cylinders with compressed oxygen are also used to strengthen the gas flame welding apparatus. Oxygen is widely used in the steel industry, where a high temperature in the blast furnaces is maintained with compressed O ₂ . The maximum degree of oxidation of oxygen is -2. This characteristic is actively used for the production of oxides for the purpose of their further burning and the release of thermal energy. Liquid oxygen, ozone and other compounds containing large amounts of O _{2 are} used as propellant oxidants. Oxidized by oxygen some organic compounds are used as explosives.

In the chemical industry, oxygen is used as an oxidizer of hydrocarbons in acid-containing compounds, such as alcohols, acids, etc. In medicine, it is used under reduced pressure to treat patients with lung problems, to maintain the vital activity of the body. In agriculture, small doses of pure oxygen are used for breeding fish in ponds, to increase the proportion of cattle, etc.

Oxygen is a powerful oxidizer, without which it is impossible to exist

Above much has been written about what oxygen displays oxidation states when reacting with various compounds and elements, what kinds of oxygen compounds exist, which kinds are life-threatening and which are not. One can remain incomprehensible - how, for all its toxicity and high level of oxidation, oxygen is one of the elements without which life on Earth is impossible? The fact is that our planet is a very balanced organism, which has adapted specifically to those substances that are contained in the atmospheric layer. It participates in a cycle that looks like this: a person and all other animals consume oxygen and produce carbon dioxide, and plants in the vast majority consume carbon dioxide and produce oxygen. Everything in the world is interconnected, and the loss of one link of this chain can lead to the rupture of the whole chain. We should not forget about this and take care of life on the planet entirely, and not only its individual representatives.