In nature, there are simple and complex substances.The main difference between them - in their composition.Thus, simple substances include atoms of elements.Their (simple substance) crystals can be synthesized in the laboratory, and sometimes at home.Often, however, to store the obtained crystals need to create certain conditions.
There are five classes, which are separated by a simple matter: metals, semi-metals, non-metals, intermetallic compounds and halogens (not naturally occurring).They can be represented by atomic (Ar, He) or molecular (O2, H2 O3) gas.
As an example, take a simple substance oxygen.This includes molecules consisting of two atoms of oxygen element.Or, for example, the substance consists of iron crystals comprising only atoms of the element iron.Historically it called a simple matter for the title element whose atoms are part of it.The structure of these compounds can be molecular and non-molecular.
Sophisticated materials include various types of atoms and can form upon decomposition of two (or more) compound.For example, water in the cleavage generates oxygen and hydrogen.Thus each compound can not be decomposed into simpler substances.For example, the iron sulfide formed by atoms of sulfur and iron, can not be digested.In this case, in order to prove that the compound is a complex heterogeneous atoms and includes, apply the principle of the reverse reaction.In other words, using the starting components obtained iron sulfide.
Simple substances are forms of chemical elements that exist in a free state.Today, science knows more than four hundred species of these elements.
Unlike complex substances simply can not get 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, a triatomic ozone, oxygen and generates diatomic oxygen and carbon can form diamond and graphite).This property is called allotropism.Allotropic modifications differ in structure and method of placement of molecules in crystals, or the composition of the molecules themselves (atomic) element.The ability of the formation of several types of simple substances due to the atomic structure, which determines the type of chemical bond, as well as the peculiarities of the structure of molecules and crystals.
All allotropic modifications have the ability to transform into each other.Different types of simple substances formed one chemical element may have different physical properties and different levels of chemical activity.For example, oxygen exhibits less than ozone, activity, and the melting point of the fullerene, for example, less than that of diamond.
Under normal conditions, eleven elements simple substance will constitute gases (Ar, Xe, Rn, N, H, Ne, O, F, Kr, Cl, He,), for the two liquids (Br, Hg), and forother elements - solids.
At temperatures close to the room, the five metals are taking a liquid or semi-liquid state.This is due to the fact that their melting points are almost equal to room temperature.Thus, mercury and rubidium melt at 39 degrees, France - at 27, cesium - at 28, and gallium at 30 degrees.
should be noted that the concept of "chemical element", "atom", "simple substance" should not be confused.Thus, for example, it has a specific atom, and the specific value actually exists.The definition of "chemical element" is generally abstract collective.The nature of the elements present in the form of free atoms or chemically bound.At the same time the characteristics of simple substances (aggregate particles) and chemical elements (a particular type of isolated atoms) have their own characteristics.
