Simple substances

In nature, there are simple and complex substances. The main difference between them is in their composition. Thus, simple substances include atoms of one element. Their (simple substances) crystals can be synthesized in laboratory, and sometimes at home. However, it is often necessary to create certain conditions for storing the crystals obtained.

There are five classes to which simple substances are divided: metals, semimetals, nonmetals, intermetallides and halogens (not found in nature). They can be represented by atomic (Ar, He) or molecular (O2, H2, O3) gases.

As an example, one can take a simple oxygen substance. It includes molecules consisting of two atoms of the element Oxygen. Or, for example, the substance iron consists of crystals, which include only the atoms of the Iron element. Historically, it is customary to call a simple substance by the name of the element whose atoms are included in its composition. The structure of these compounds can be molecular and non-molecular.

Complex substances include atoms of different types and can form two (or more) compounds during decomposition. For example, water splits form oxygen and hydrogen. In this case, not every compound can be decomposed into simple substances. For example, iron sulphide, formed by sulfur and iron atoms, can not be split. In this case, in order to prove that the compound is complex and includes heterogeneous atoms, the principle of reverse reaction is applied. In other words, iron sulphide is obtained with the help of the starting components.

Simple substances are forms of chemical elements that exist in a free form. Today, science knows more than four hundred kinds of these elements.

Unlike complex substances, simple substances can not be obtained from other simple substances. They also can not be decomposed into other compounds.

One chemical element can form different types of simple substances. (For example, the element Oxygen forms triatomic ozone and diatomic oxygen, and Carbon is capable of forming diamond and graphite). This property is called allotropy. Allotropic modifications differ in the structure and method of accommodation of molecules in crystals or in the composition of the molecules (atoms) of the element itself. The ability to form several types of simple substances is due to the atomic structure, which determines the type of chemical bond, as well as the structural features of molecules and crystals.

All allotropic modifications have the property of changing into one another. Different types of simple substances formed by a single chemical element can have different physical properties and different levels of chemical activity. For example, oxygen shows less activity than ozone, and the melting temperature of fullerene, for example, is less than that of diamond.

Under normal conditions, for eleven elements, simple substances will be gases (Ar, Xe, Rn, N, H, Ne, O, F, Kr, Cl, He,), for two liquids (Br, Hg), and for other elements - solid bodies.

At a temperature close to room temperature, five metals will take a liquid or semi-liquid state. This is due to the fact that their melting point is almost equal to room temperature. Thus, mercury and rubidium melt at 39 degrees, France at 27, cesium at 28, and gallium at 30 degrees.

It should be noted that the concepts of "chemical element", "atom", "simple substance" should not be confused. So, for example, an atom has a definite, concrete meaning and exists realistically. The definition of "chemical element" is generally abstract, collective. In nature, the elements are present in the form of free or chemically bonded atoms. In this case, the characteristics of simple substances (a collection of particles) and chemical elements (isolated atoms of a particular type) have their own characteristics.