Atoms of one kind can be part of different substances. For an element denoted by the symbol "O" (from the Latin name Oxygenium), two common substances that are common in nature are known. The formula of one of them is O 2, the second is O 3. These are allotropic modifications of oxygen (allotropes). There are other compounds that are less stable (O 4 and O 8 ). Comparison of molecules and properties of substances will help to understand the difference between these forms .
What are allotropic modifications?
Many chemical elements can exist in two, three or more forms. Each of these modifications is formed by atoms of the same species. The scientist J. Berzellius in 1841 was the first to call such a phenomenon allotropy. An open regularity was initially applied only to characterize substances of molecular structure. For example, two allotropic modifications of oxygen are known whose atoms form molecules. Researchers later found that modifications could be among the crystals. According to modern concepts, allotropy is one of the cases of polymorphism. The differences between the forms are caused by the mechanisms of the formation of chemical bonds in molecules and crystals. This feature is mainly manifested by elements of 13-16 groups of the periodic table.
How does a different combination of atoms affect the properties of matter?
Allotropic modifications of oxygen and ozone are formed by atoms of an element with a serial number of 8 and the same number of electrons. But they differ in structure, which led to a significant discrepancy in properties.
Comparison of oxygen and ozone| Signs | Oxygen | Ozone |
Molecule Composition | 2 oxygen atoms | 3 oxygen atoms |
| Structure | |
| State of aggregation and color | Colorless transparent gas or pale blue liquid | Blue gas, blue liquid, dark violet solid |
| Smell | Is absent | Sharp, reminiscent of a thunderstorm, freshly cut hay |
Melting point (° C) | -219 | -193 |
| Boiling Point (° C) | -183 | -112 |
Density (g / l) | 1.4 | 2.1 |
Solubility in water | Slightly soluble | Better than oxygen |
Chemical activity | Under normal conditions, stable | Easily decomposes to form oxygen |
Conclusions from the comparison: allotropic modifications of oxygen do not differ in qualitative composition. The structure of the molecule is reflected in the physical and chemical properties of substances.
Is there the same amount of oxygen and ozone in nature?
A substance whose formula is O 2 is found in the atmosphere, hydrosphere, earth's crust and living organisms. About 20% of the atmosphere is formed by diatomic oxygen molecules. In the stratosphere at an altitude of about 12–50 km from the earth’s surface, there is a layer called the “ozone screen”. Its composition reflects the formula O 3 . Ozone protects our planet by intensively absorbing the dangerous rays of the red and ultraviolet spectrum of the Sun. The concentration of the substance is constantly changing, and its average value is low - 0.001%. Thus, O 2 and O 3 are allotropic modifications of oxygen, which have significant differences in distribution in nature.
How to get oxygen and ozone?
Molecular oxygen is the most important simple substance on Earth. Formed in the green parts of plants in the light
during photosynthesis. During electric discharges of natural or artificial origin, the diatomic oxygen molecule decays. The temperature at which the process begins is about 2000 ° C. Part of the arising radicals combines again, forming oxygen. Some active particles react with diatomic oxygen molecules. This reaction produces ozone, which also reacts with oxygen free radicals. In this case, diatomic molecules arise. Reversibility of reactions leads to the fact that the concentration of atmospheric ozone is constantly changing. In the stratosphere, the formation of a layer consisting of O
3 molecules is associated with the ultraviolet radiation of the Sun. Without this protective shield, dangerous rays could reach the surface of the Earth and destroy all life forms.
Allotropic modifications of oxygen and sulfur
The chemical elements O (Oxygenium) and S (Sulfur) are located in the same group of the periodic table; they are characterized by the formation of allotropic forms. Of the molecules with a different number of sulfur atoms (2, 4, 6, 8) under ordinary conditions, the most stable is S8, resembling a corona in shape. Rhombic and monoclinic sulfur are built from such 8-atomic molecules.
At a temperature of 119 ° C, the monoclinic form of yellow forms a brown malleable mass - a plastic modification. The study of allotropic modifications of sulfur and oxygen is of great importance in theoretical chemistry and practical activity.
On an industrial scale, the oxidizing properties of various forms are used. Ozone is used to disinfect air and water. But at concentrations above 0.16 mg / m3, this gas is dangerous for humans and animals. Molecular oxygen is essential for respiration, and is used in industry and medicine. An important role in economic activity is played by allotropes of carbon (diamond, graphite), phosphorus (white, red) and other chemical elements.