Simple and complex substances. Chemical element
All the substances we talk about in school course Chemistry is usually divided into simple and complex. Simple substances are those substances whose molecules contain atoms of the same element. Atomic oxygen (O), molecular oxygen (O2) or simply oxygen, ozone (O3), graphite, diamond are examples of simple substances that form the chemical elements oxygen and carbon. Complex substances are divided into organic and inorganic. Among inorganic substances, the following four classes are primarily distinguished: oxides (or oxides), acids (oxygen and oxygen-free), bases (water-soluble bases are called alkalis) and salts. Compounds of non-metals (excluding oxygen and hydrogen) are not included in these four classes; we will call them conventionally “and other complex substances”.
Simple substances are usually divided into metals, non-metals and inert gases. Metals include all chemical elements in which the d- and f-sublevels are being filled, these are the elements in the 4th period: Sc - Zn, in the 5th period: Y - Cd, in the 6th period: La - Hg, Ce - Lu, in the 7th period Ac - Th - Lr. If we now draw a line from Be to At among the remaining elements, then to the left and below there will be metals, and to the right and above - non-metals. Inert gases are located in group 8 of the Periodic Table. Elements located on the diagonal: Al, Ge, Sb, Po (and some others. For example, Zn) in a free state have the properties of metals, and hydroxides have the properties of both bases and acids, i.e. are amphoteric hydroxides. Therefore, these elements can be considered metal-non-metals, occupying an intermediate position between metals and non-metals. Thus, the classification of chemical elements depends on what properties their hydroxides will have: basic - which means it is a metal, acidic - a non-metal, and both (depending on the conditions) - metal-non-metal. The same chemical element in compounds with the lowest positive oxidation state (Mn+2, Cr+2) exhibits pronounced “metallic” properties, and in compounds with the maximum positive oxidation state (Mn+7, Cr+6) exhibits the properties of a typical non-metal. To see the relationship simple substances, oxides, hydroxides and salts, we present a summary table.
Under chemical element understand a collection of atoms with the same positive nuclear charge and with a certain set of properties. Atoms of the same chemical element combine to form simple substance. When atoms of different chemical elements combine, complex substances (chemical compounds) or mixtures. The difference between chemical compounds and mixtures is that:
They have new properties that the simple substances from which they were obtained did not have;
They cannot be mechanically divided into their component parts;
Chemical elements in their composition can only be in strictly defined quantitative ratios.
Some chemical elements (carbon, oxygen, phosphorus, sulfur) can exist in the form of several simple substances. This phenomenon is called allotropy, and varieties of simple substances of the same chemical element are called its allotropic modifications(modifications).
Tasks
1.1. What more exists in nature: chemical elements or simple substances? Why?
1.2. Is it true that sulfur and iron are included in the composition of iron sulfide as substances? If not, what is the correct answer?
1.3. Name allotropic modifications of oxygen. Do they differ in their properties? If so, how?
1.4. Which of the allotropic modifications of oxygen is chemically more active and why?
1.5. The simple substances or chemical elements are zinc, sulfur and oxygen in the following reactions:
1) CuSO 4 + Zn = ZnSO 4 + Cu;
2) S + O 2 = SO 2;
3) Zn + 2HC1 = ZnCl 2 + H 2 ;
4) Zn + S = ZnS;
5) 2H 2 0 = 2H 2 + O 2 .
1.6. Is it possible to get another simple substance from one simple substance? Give a reasoned answer.
1.7. When a certain substance is burned in oxygen, sulfur (IV) oxide, nitrogen and water are obtained. What chemical elements form the starting substance?
1.8. Indicate whether simple or complex substances include: H 2 O, C1 2, NaOH, O 2, HNO 3, Fe, S, ZnSO 4, N 2, AgCl, I 2, A1 2 O 3, O 3?
1.9. For which chemical elements are allotropic modifications known? Name these modifications.
1.10. Is it possible for a chemical element to transition from one allotropic modification to another? Give examples.
1.11. What chemical elements do they mean when they talk about diamond and ozone?
1.12. Which of the substances are chemical compounds and which are mixtures:
2) air;
4) sulfuric acid;
1.13. How to prove that sodium chloride is a complex substance?
1.14. Name three allotropic modifications of carbon.
1.15. What are allotropic modifications of phosphorus called and how do they differ from each other?
1.16. What are allotropic modifications of sulfur called and how do they differ from each other?
1.17. Indicate which of the statements is true and why - the composition of barium sulfate includes:
1) simple substances barium, sulfur, oxygen;
2) chemical elements barium, sulfur, oxygen.
1.18. How many liters of ammonia can be produced from a mixture of 10 liters of nitrogen and 30 liters of hydrogen?
1.19. How many liters of water vapor are produced from a mixture of 10 liters of hydrogen and 4 liters of oxygen? What gas and in what volume will remain in excess?
1.20. How many grams of zinc sulfide (ZnS) can be formed from a mixture of 130 g of zinc and 48 g of sulfur?
1.22. What is a solution of alcohol in water - a mixture or a chemical compound?
1.23. Can a complex substance consist of atoms of the same type?
1.24. Which of the following substances are mixtures and which are chemical compounds:
1) bronze;
2) nichrome;
3) kerosene;
4) potassium nitrate:
5) rosin;
6) superphosphate.
1.25. Given a mixture of Cl 2 + HCl + CaCl 2 + H 2 O.
1) How many different substances are in the mixture;
2) How many chlorine molecules are in the mixture;
3) How many chlorine atoms are in the mixture;
4) How many molecules of different substances are contained in the mixture.
When studying the material in the previous paragraphs, you have already become acquainted with some substances. For example, a molecule of hydrogen gas consists of two atoms of the chemical element hydrogen - H + H = H2.
Simple substances are substances that contain atoms of the same type
Simple substances known to you include: oxygen, graphite, sulfur, nitrogen, all metals: iron, copper, aluminum, gold, etc. Sulfur consists only of atoms of the chemical element sulfur, while graphite consists of atoms of the chemical element carbon.
It is necessary to clearly distinguish between concepts "chemical element" And "simple matter". For example, diamond and carbon are not the same thing. Carbon is a chemical element, and diamond is a simple substance formed by the chemical element carbon. IN in this case a chemical element (carbon) and a simple substance (diamond) are called differently. Often a chemical element and its corresponding simple substance are named the same. For example, the element oxygen corresponds to a simple substance - oxygen.
It is necessary to learn how to distinguish between where we are talking about an element and where about a substance! For example, when they say that oxygen is part of water, we are talking about the element oxygen. When they say that oxygen is a gas necessary for breathing, we are talking about the simple substance oxygen.
Simple substances of chemical elements are divided into two groups - metals and non-metals.
Metals and non-metals radically different in their physical properties. All metals are solid substances under normal conditions, with the exception of mercury - the only liquid metal. Metals are opaque and have a characteristic metallic luster. Metals are ductile and conduct heat and electricity well.
Nonmetals are not similar to each other in physical properties. So, hydrogen, oxygen, nitrogen are gases, silicon, sulfur, phosphorus are solids. The only liquid non-metal is bromine, a brownish-red liquid.
If you draw a conventional line from the chemical element boron to the chemical element astatine, then in the long version of the Periodic System there are non-metallic elements above the line, and below it - metal. In the short version of the Periodic Table, there are non-metallic elements below this line, and both metallic and non-metallic elements above it. This means that it is more convenient to determine whether an element is metallic or non-metallic using the long version of the Periodic Table. This division is arbitrary, since all elements in one way or another exhibit both metallic and non-metallic properties, but in most cases this distribution corresponds to reality.
Complex substances and their classification
If the composition of simple substances includes atoms of only one type, it is easy to guess that the composition of complex substances will include several types of different atoms, at least two. An example of a complex substance is water; you know its chemical formula - H2O. Water molecules are made up of two types of atoms: hydrogen and oxygen.
Complex substances- substances containing atoms of various types
Let's conduct the following experiment. Mix sulfur and zinc powders. Place the mixture on a metal sheet and set it on fire using a wooden torch. The mixture ignites and quickly burns with a bright flame. After the completion of the chemical reaction, a new substance was formed, which included sulfur and zinc atoms. The properties of this substance are completely different from the properties of the starting substances - sulfur and zinc.
Complex substances are usually divided into two groups: inorganic substances and their derivatives and organic substances and their derivatives. For example, rock salt is an inorganic substance, and the starch contained in potatoes is an organic substance.
Types of structure of substances
Based on the type of particles that make up the substances, substances are divided into substances molecular and non-molecular structure.
The substance may contain various structural particles, such as atoms, molecules, ions. Consequently, there are three types of substances: substances of atomic, ionic and molecular structure. Substances of different types of structure will have different properties.
Substances of atomic structure
An example of substances of atomic structure are substances formed by the element carbon: graphite and diamond. These substances contain only carbon atoms, but the properties of these substances are very different. Graphite– a fragile, easily exfoliating substance of gray-black color. Diamond– transparent, one of the hardest minerals on the planet. Why do substances consisting of the same type of atom have different properties? It's all about the structure of these substances. Carbon atoms in graphite and diamond combine in different ways. Substances of atomic structure have high temperatures boiling and melting, as a rule, insoluble in water, non-volatile.
Crystal lattice – an auxiliary geometric image introduced to analyze the structure of a crystal
Substances of molecular structure
Substances of molecular structure– These are almost all liquids and most gaseous substances. There are also crystalline substances whose crystal lattice includes molecules. Water is a substance of molecular structure. Ice also has a molecular structure, but unlike liquid water, it has a crystal lattice where all molecules are strictly ordered. Substances of molecular structure have low boiling and melting points, are usually fragile, and do not conduct electricity.
Substances of ionic structure
Substances of ionic structure are solid crystalline substances. An example of an ionic compound substance is table salt. Its chemical formula is NaCl. As we can see, NaCl consists of ions Na+ and Cl⎺, alternating in certain places(nodes) of the crystal lattice. Substances with an ionic structure have high melting and boiling points, are fragile, are usually highly soluble in water, and do not conduct electric current.
The concepts of “atom”, “chemical element” and “simple substance” should not be confused.
- "Atom"– a specific concept, since atoms really exist.
- « Chemical element» – is a collective, abstract concept; In nature, a chemical element exists in the form of free or chemically bonded atoms, that is, simple and complex substances.
The names of chemical elements and the corresponding simple substances are the same in most cases.
When we talk about a material or component of a mixture - for example, a flask is filled with chlorine gas, an aqueous solution of bromine, let's take a piece of phosphorus - we are talking about a simple substance. If we say that a chlorine atom contains 17 electrons, the substance contains phosphorus, the molecule consists of two bromine atoms, then we mean a chemical element.
It is necessary to distinguish between the properties (characteristics) of a simple substance (a collection of particles) and the properties (characteristics) of a chemical element (isolated atom certain type), see table below:
Complex substances must be distinguished from mixtures, which also consist of different elements.
The quantitative ratio of the components of the mixture can be variable, but the chemical compounds have a constant composition.
For example, in a glass of tea you can add one spoon of sugar, or several, and sucrose molecules С12Н22О11 contains exactly 12 carbon atoms, 22 hydrogen atoms and 11 oxygen atoms.
Thus, the composition of compounds can be described by one chemical formula, and the composition no mixture.
The components of the mixture retain their physical and Chemical properties. For example, if you mix iron powder with sulfur, a mixture of two substances is formed. Both sulfur and iron in this mixture retain their properties: iron is attracted by a magnet, and sulfur is not wetted by water and floats on its surface.
If sulfur and iron react with each other, a new compound is formed with the formula FeS, which does not have the properties of either iron or sulfur, but has a set of its own properties. In connection FeS iron and sulfur are bound to each other, and it is impossible to separate them using the methods used to separate mixtures.
Thus, substances can be classified according to several parameters:
Conclusions from an article on the topic Simple and complex substances
- Simple substances- substances that contain atoms of the same type
- Simple substances are divided into metals and non-metals
- Complex substances- substances containing atoms of various types
- Complex substances are divided into organic and inorganic
- There are substances of atomic, molecular and ionic structure, their properties are different
- Crystal cell– an auxiliary geometric image introduced to analyze the crystal structure
The main difference between them is their composition. Thus, simple substances include atoms of one element. Their (simple substances) crystals can be synthesized in the laboratory, and sometimes at home. However, it is often necessary to create certain conditions for storing the resulting crystals.
There are five classes into which simple substances are divided: metals, semimetals, nonmetals, intermetallic compounds, and halogens (not found in nature). They can be represented by atomic (Ar, He) or molecular (O2, H2, O3) gases.
As an example, we can take the simple substance oxygen. It includes molecules consisting of two atoms of the element Oxygen. Or, for example, the substance iron consists of crystals containing only atoms of the element Iron. Historically, it was customary to name a simple substance by the name of the element whose atoms are included in its composition. The structure of these compounds can be molecular or non-molecular.
Complex substances contain atoms of different types and, when decomposed, can form two (or more) compounds. For example, when water splits, it forms oxygen and hydrogen. However, not every compound can be broken down into simple substances. For example, iron sulfide, formed by sulfur and iron atoms, cannot be broken down. In this case, in order to prove that the compound is complex and includes dissimilar atoms, the reverse reaction principle is used. In other words, iron sulfide is obtained using the starting components.
Elements are forms of chemical elements that exist in free form. Today science knows more than four hundred types of these elements.
Unlike complex substances, simple substances cannot be obtained from other simple substances. They also cannot be decomposed into other compounds.
All allotropic modifications have the property of transforming into each other. Different types simple substances formed by one chemical element can have different and different levels of chemical activity. For example, oxygen exhibits less activity than ozone, and the melting point of fullerene, for example, is lower than that of diamond.
Under normal conditions, for eleven elements the 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 - solids.
At temperatures close to room temperature, the five metals will take on a liquid or semi-liquid state. This is due to the fact that their melting point is almost equal. Thus, mercury and rubidium melt at 39 degrees, francium 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, specific meaning and really exists. The definition of “chemical element” is generally abstract and collective. In nature, elements are present in the form of free or chemically bonded atoms. At the same time, the characteristics of simple substances (collections of particles) and chemical elements (isolated atoms of a particular type) have their own characteristics.