", "a drug ". Using the modern definition was recorded in 1884 (it. Valenz.). In 1789, William Higgins published a job in which suggested the existence of connections between the smallest particles of the substance.

However, the exact and later, fully confirmed understanding of the phenomenon of valence was proposed in 1852 by Chemik Edward Frankland in the work, in which he collected and rethought all the theories that existed at that time and assumptions on this matter. . Observing saturation ability different metals and comparing the composition of organic metal derivatives with the composition not organic compounds, Frankland has introduced the concept of " connective power", Posing this foundation to the teaching of valence. Although Frankland has established some private patterns, his ideas did not receive development.

A decisive role in the creation of valence theory was played by Friedrich August Kekule. In 1857, he showed that carbon is a four-friendly (four-coat) element, and its simplest compound is methane CH 4. Confident of the truth of his ideas about the valence of atoms, Kekule introduced them to his tutorial of organic chemistry: basicity, according to the author - the fundamental property of the atom, the property is the same permanent and immutable, as well as atomic weight. In 1858, the views, almost coinciding with the ideas of Kekule, expressed in the article " On the new chemical theory»Archibald Scott Cooper.

For three years later, in September 1861, A. M. Butlers at the valence theory of the most important additions. He conducted a clear distinction between a free atom and an atom that entered into connection with the other when its affinity " binds and goes into new form " Butlers introduced an idea of \u200b\u200bthe completeness of the use of the affinity forces and about " screen affinity"That is, the energy non-equivalence of bonds, which is due to the mutual influence of atoms in the molecule. As a result of this mutual influence, atoms depending on their structural environment acquire various "Chemical meaning" Butlerov Theory allowed to give an explanation to many experimental facts regarding the isomerism of organic compounds and their reactivity.

The vivid image of the molecule was the enormous advantage of the valence theory. In the 1860s The first molecular models appeared. Already in 1864, A. Brown suggested using structural formulas in the form of circles with elements placed in them, connected by lines denoting chemical bond between atoms; The number of lines corresponded to the valence of an atom. In 1865, A. Von Hoffman demonstrated the first chasoslerge models in which crocket balls played the role of atoms. In 1866, in the textbook, Kekule appeared drawings of stereochemical models, in which the carbon atom had a tetrahedral configuration.

Modern valence views

Since the emergence of the theory of chemical bond, the concept of "valence" has undergone a substantial evolution. Currently, it does not have a strict scientific interpretation, therefore, almost completely displaced from scientific vocabulary and is used, mainly for methodical purposes.

Basically, under valence chemical elements Meals the ability of its free atoms to the formation of a certain number of covalent bonds. In connections with covalent bonds, the valence of atoms is determined by the number of two-electron two-centered bonds. It is this approach that was adopted in the theory of localized valence relations proposed in 1927 by V. Gaitler and F. London in 1927. It is obvious that if there is an atom n. unpaired electrons I. m. meaning electronic pairs, then this atom can form n + M. Covalent bonds with other atoms. In assessing the maximum valence, it should be processed from the electronic configuration of the hypothetical, so-called. "Excited" (valence) state. For example, maximum valence The beryllium, boron and nitrogen atom is 4 (for example, in B (OH) 4 2-, BF 4 - and NH 4 +), phosphorus - 5 (PCL 5), sulfur - 6 (H 2 SO 4), chlorine - 7 (Cl 2 O 7).

In some cases, such characteristics of the molecular system as the degree of oxidation of the element, an effective charge on the atom, the coordination number of the atom, etc., are identified with the valence, the coordination number of the atom, etc., these characteristics may be close and even coincided quantitatively, but in no way be identical to each other. For example, in the isoelectronic nitrocees of nitrogen N 2, carbon monoxide CO and cyanide-ion Cn - a triple bond is realized (that is, the valence of each atom is 3), however, the degree of oxidation of the elements is equal, respectively, 0, +2, -2, +2 and -3. In the ethane molecule (see Fig.) Carbon fourhounds, as in most organic compounds, while the degree of oxidation is formally equal to -3.

This is especially true for molecules with delocalized chemical bonds, for example, in nitric acid, the degree of nitrogen oxidation is +5, while nitrogen can not have valence above 4. The rule of many school textbooks is "maximum valence The element is numerically equal to the number of the group in the periodic table "- refers exclusively to the degree of oxidation. The concepts of "permanent valence" and "variable valence" are also preferably refer to the degree of oxidation.

see also

Notes

Links

• UGAY Ya. A. Valency, chemical bond and the degree of oxidation are the most important concepts of chemistry // Syrian educational magazine. - 1997. - № 3. - P. 53-57.
• / Levchenkov S.I. Short essay of the history of chemistry

Literature

• L. Powling Nature of chemical bond. M., L.: State NTI Chem. Literature, 1947.
• Cartmell, Fowes. Valence and structure of molecules. M.: Chemistry, 1979. 360 p.]
• Coleson Ch. Valence. M.: Mir, 1965.
• Marrell J., Kettle S., Tedder J. Theory of valence. Per. from English M.: Peace. 1968.
• Development of valence learning. Ed. Kuznetsova V. I. M.: Chemistry, 1977. 248c.
• The valence of atoms in molecules / Korolkov D.V. Basics of inorganic chemistry. - M.: Enlightenment, 1982. - P. 126.

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Watch what is "valence" in other dictionaries:

Valuation, measure of "connecting ability" of a chemical element equal to the number of individual chemical bonds that one atom may form. The valence of the atom is determined by the number of electrons at the highest (valence) level (outer ... ... Scientific and Technical Encyclopedic Dictionary

VALENCE - (from lat. Valere to have a value), or atomicity, the number of hydrogen atoms or atoms equivalent to it or radicals, can be connected to this atom or radical. B. is one of the foundations of the distribution of elements in the periodic system D. I. ... ... Big medical encyclopedia

Valence - * Valennasc * Valence The term comes from the lat. Practhing. 1. In chemistry, this is the ability of atoms of chemical elements to form a certain number of chemical bonds with atoms of other elements. In the light of the structure of the atom V. This is the ability of atoms ... ... Genetics. encyclopedic Dictionary

- (from lat. Valentia force) In physics, the number showing, with some hydrogen atoms, this atom can be connected or to replace them. In psychology, valence is the designation for prompting from England. Philosophical ... ... Philosophical encyclopedia

Atomic dictionary of Russian synonyms. Valuation of Sushch., Number of synonyms: 1 Atomic (1) Dictionary of Synonyms ASIS. V.N. Trishin ... Synonym dictionary

VALENCE - (from Lat. Valentia is strong, durable, influential). The ability of a word to a grammatical combination with other words in the proposal (for example, in the verbs, the valence determines the ability to combine with the subject, direct or indirect addition) ... New dictionary of methodical terms and concepts (theory and practice of learning languages)

- (from Latin Valentia force), the ability of the chemical element atom to attach or replace a certain number of other atoms or atomic groups with the formation of a chemical connection ... Modern encyclopedia

- (from lat. Valentia force) The ability of the atom of the chemical element (or atomic group) to form a certain number of chemical bonds with other atoms (or atomic groups). Instead of valence, they often use narrower concepts, for example ... ... Big Encyclopedic Dictionary

From the materials of the lesson, you learn that the constancy of the composition of the substance is explained by the presence of certain valence in atoms of the chemical elements; Get acquainted with the concept of "valence of atoms of chemical elements"; Learn to determine the valence of the element by the formula of the substance, if the valence of another element is known.

Topic: Initial Chemical Presentations

Lesson: valence of chemical elements

The composition of most substances is constant. For example, water molecule always contains 2 hydrogen atoms and 1 oxygen atom - H 2 O. The question arises: why are substances have a permanent composition?

Let us analyze the composition of the proposed substances: H 2 O, NAH, NH 3, CH 4, HCl. All of them consist of atoms of two chemical elements, one of which is hydrogen. One atom of the chemical element can accounted for 1,2,3rd hydrogen atom. But in no substance will not for one hydrogen atom come out several atoms of another chemical element. Thus, the hydrogen atom can attach the minimum number of atoms of another element, or rather, only one.

The property of the atoms of the chemical element to attach a certain number of atoms of other elements is called valence.

Some chemical elements have constant valence values \u200b\u200b(for example, hydrogen (I) and oxygen (II)), others may exhibit several valence values \u200b\u200b(for example, iron (II, III), sulfur (II, IV, VI), carbon (II, Iv)), they are called elements with variable valence. Valuation values \u200b\u200bof some chemical elements are given in the textbook.

Knowing the valence of chemical elements can be explained why the substance has exactly such a chemical formula. For example, the formula of the water H 2 O. Denote the valence capabilities of the chemical element using a drop. Hydrogen has valence I, and oxygen - II: N- and -. Each atom can fully utilize its valence capabilities, if one atom of oxygen will account for two hydrogen atoms. The sequence of the compound of atoms in the water molecule can be represented as a formula: n-oh.

The formula that shows the sequence of connecting atoms in the molecule is called graphic(or structural).

Fig. 1. Graphic water formula

By knowing the formula of a substance consisting of atoms of two chemical elements, and the valence of one of them can determine the valence of another element.

Example 1.We define the valence of carbon in the substance CH 4. Knowing that the valence of hydrogen is always equal to I, and carbon attached 4 hydrogen atoms to itself, it can be argued that carbon valence is equal to IV. The valence of atoms is indicated by the Roman number above the sign of the element :.

Example 2.We define the valence of phosphorev compound p 2 o 5. To do this, you must perform the following actions:

1. Above the sign of oxygen to record the value of its valence - II (oxygen has a constant value of valence);

2. Multiplying oxygen valence by the number of oxygen atoms in the molecule, to find the total number of valence units - 2 · 5 \u003d 10;

3. To divide the resulting total number of valence units on the number of phosphorus atoms in the molecule - 10: 2 \u003d 5.

Thus, the valence of phosphorus in this connection is equal to V -.

1. Emelyanova E.O., Iodko A.G. Organization of cognitive activity of students in chemistry lessons in 8-9 classes. Support abstracts with practical tasks, tests: Part I. - M.: School Press, 2002. (p.33)

2. Ushakova O.V. Workbook in Chemistry: 8th CL.: To the textbook P.A. Orzhekovsky and others. "Chemistry. Grade 8 "/ O.V. Ushakova, P.I. Bespalov, P.A. Oroekovsky; under. ed. prof. P.A. Orojekovsky - M.: AST: Astrel: ProfiSdat, 2006. (p. 36-38)

3. Chemistry: 8th grade: studies. For composure. Institutions / P.A. Oroekovsky, L.M. Meshcheryakova, L.S. Ponya. M.: AST: Astrel, 2005. (§16)

4. Chemistry: noorg. Chemistry: studies. For 8 cl. general education. institutions / G.E. Rudzitis, F.G. Feldman. - M.: Enlightenment, Moscow Tutorials, 2009. (§§11,12)

5. Encyclopedia for children. Volume 17. Chemistry / Chapters. Red.V.A. Volodin, Ved. Scientific ed. I. Leenson. - M.: Avanta +, 2003.

Additional Web Resources

1. Unified collection of digital educational resources ().

2. Electronic version of the magazine "Chemistry and Life" ().

Homework

1. p.84 № 2from the textbook "Chemistry: 8th grade" (P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Ponc. M.: Ast: Astrel, 2005).

2. from. 37-38 №№ 2,4,5,6of Working notebook In Chemistry: 8th CL.: To the textbook P.A. Orzhekovsky and others. "Chemistry. Grade 8 "/ O.V. Ushakova, P.I. Bespalov, P.A. Oroekovsky; under. ed. prof. P.A. ORZHEKOVSKOGO - M.: AST: Astrel: ProfiSdat, 2006.

Considering the formulas of various compounds, it is not difficult to notice that number of atoms The same element in the molecules of various substances is not equally. For example, HCl, NH 4 Cl, H 2 S, H 3 PO 4, etc. The number of hydrogen atoms in these compounds varies from 1 to 4. This is characteristic not only for hydrogen.

How to guess which index put next to the designation of the chemical element?How are the formulas of the substance are compiled? It is easy to do when you know the valence of elements that are part of the molecule of this substance.

– This property of the atom of this element is to attach, hold or replace in chemical reactions a certain number of atoms of another element. The valence of the hydrogen atom is adopted per unit of valence. Therefore, sometimes the definition of valence is formulated as: valence – This property of the atom of this element is to attach or replace a certain number of hydrogen atoms.

If one hydrogen atom is attached to one atom of this element, the element is monovalent, if two – two-duty I.etc. Hydrogen compounds are known not for all elements, but almost all elements form compounds with oxygen O. oxygen is considered constantly bivalent.

Permanent valence:

I. – H, na, li, k, rb, cs
II. – O, BE, MG, CA, SR, BA, RA, ZN, CD
III – B, AL, GA, IN

But what to do if the element does not connect with hydrogen? Then the valence of the desired element is determined by the valence of the known element. Most often, it is found using oxygen valence, because in the compounds its valence is always 2. For example, It will not be difficult to find the valence of elements in the following compounds: Na 2 O (Na valence – 1, O. – 2), Al 2 O 3 (Al valence – 3, O. – 2).

The chemical formula of this substance can be made, only knowing the valence of elements. For example, make formulas such compounds such as CaO, Bao, CO, simply, because the number of atoms in molecules is equally, since the valence of elements is equal.

And if valence is different? When do we act in this case? It is necessary to remember the following rule: in the formula of any chemical compound, the product of the valence of one element by the number of its atoms in the molecule is equal to the product of the valence to the number of atoms of another element. For example, if it is known that the mn valence in the compound is 7, and o – 2, then the compound formula will look like Mn 2 O 7.

How did we get the formula?

Consider the algorithm for the compilation of valence formulas for consisting of two chemical elements.

There is a rule that the number of valencies in one chemical element is equal to the number of valences in another. Consider on the example of the formation of a molecule consisting of manganese and oxygen.
We will be in accordance with the algorithm:

1. Record near the symbols of chemical elements:

Mn O.

2. We put on the chemical elements of their valence numbers (the valence of the chemical element can be found in the table of the periodic Mendeleva system, manganese – 7, at oxygen – 2.

3. We find the smallest common multiple (the smallest number that is divided without a balance of 7 and 2). This is a number 14. We divide it on the valence of elements 14: 7 \u003d 2, 14: 2 \u003d 7, 2 and 7, they are indexes, respectively, phosphorus and oxygen. We substitute indexes.

Knowing the valence of one chemical element, following the rule: the valence of one element × the number of its atoms in the molecule \u003d the valence of another element × the number of atoms of this (other) element, one can determine the valence of the other.

Mn 2 O 7 (7 · 2 \u003d 2 · 7).

2x \u003d 14,

x \u003d 7.

The concept of valence was introduced into chemistry before the structure of the atom was known. It is now established that this property of the element is associated with the number of external electrons. For many elements, the maximum valence follows from the position of these elements in the periodic system.

In order to determine the valence of a substance, you need to look at the periodic table of the chemical elements of Mendeleev, the designations of Roman numbers will be the valencies of certain substances in this table. For example, but, hydrogen (H) will always be monovalent A, and oxygen (o) is always bivalent. This is the below some crib, which, how I suppose will help you)

First of all, it is worth noting that the chemical elements may have both a constant and variable valence. As for the permanent valence, such elements you simply need to memorize

Alkali metals, hydrogen, as well as halogens are monovalent;

But Trozaleten Bor and aluminum.

So, now let's go through the Mendeleev table to determine valence. The highest valence for the element is always equal to its group number

The lowest valence will be found in the end of the subtraction from the 8th group number. Lower valence endowed non-metals to a greater extent.

Chemical elements can be a constant or valence variable. Elements C. permanent valence It is necessary to learn. Always

• monovalent Hydrogen, halogen, alkali metals
• bivalent Oxygen, alkaline earth metals.
• trusted Aluminum (AL) and Bor (B).

Valence can be determined by the Mendeleev table. The highest valence of the element is always equal to the number of the group in which it is located.

Low variable valence most often have non-metals. To learn a low valence, out of 8 deduct the number of the group - as a result there will be a desired value. For example, sulfur is in the 6th group and E of the highest valence - vi, the lowest valence will be II (86 \u003d 2).

According to school definition, the valence is the ability of the chemical element to form this or that amount of chemical bonds with other atoms.

As is known, the valence is permanent (when the chemical element is always formed by the same number of connections with other atoms) and the variable (when, depending on a particular substance, the valence of the same element varies).

Determine the valence will help us a periodic system of chemical elements D. I. Mendeleev.

There are such rules:

1) Maximum The valence of the chemical element is equal to the number of the group. For example, Chlorine is in the 7th group, which means that it has a maximum valence equal to 7. sulfur: it in the 6th group, it means that no maximum valence is equal to 6.

2) Mining Valence for nemmetalov equal to 8 minus group number. For example, the minimum valence of the same chlorine is 8 7, that is, 1.

Alas, from both rules there are exceptions.

For example, copper is in the 1st group, but the maximum valence of copper is not equal to 1, and 2.

Oxygen is in the 6th group, but he has almost always valence 2, and not at all 6.

It is useful to remember even the following rules:

3) All alkaline Metals (Metals I Group I, the main subgroup) always have valence 1.. For example, sodium valence is always equal to 1, because it is an alkaline metal.

4) All plot and land Metals (Metals II Groups, the main subgroup) always have valence 2.. For example, magnesium valence is always 2, because it is a pure land metal.

5) Aluminum always has valence 3.

6) Hydrogen always has valence 1.

7) Oxygen almost always has valence 2.

8) Carbon almost always has valence 4.

It should be remembered that in different sources, the definition of valence may differ.

More or less accurate valence can be defined as the number of common electronic pairs by which this atom is associated with other.

According to this definition, the valence of nitrogen in HNO3 is 4, and not 5. Five-length nitrogen can not be, because 10 electrons would circle around the nitrogen atom. And this cannot be, because the maximum of electrons is 8.

The valence of any chemical element is its property, and more accurately the property of its atoms (atoms of this element) to hold some number of atoms, but already another chemical element.

There are chemical elements both with a constant and variable valence, which varies depending on the connection with which element it is (this element) is or entering.

Valinations of some chemical elements:

We now turn to how the valence of the element is determined on the table.

So, the valence can be determined by table Mendeleev:

• the highest valence corresponds to (equal) the number of the group;
• the lower valence is determined by the formula: group number - 8.





From the school course in chemistry, we know that all chemical elements can be with a constant or variable valence. Elements in which constant valence needs to be simply remembered (for example, hydrogen, oxygen, alkali metals and other elements). Valence is easy to identify on the Mendeleev table, which is in any textbook in chemistry. The highest valence corresponds to its group number in which it is located.

The valence of any element can be determined by the Mendeleev table itself, by group number.

At the very least, it is possible to act in the case of metals, because their valence is equal to the number of the group.

With non-metals a little different story: their highest valence (in oxygen compounds) is also equal to the number of the group, but the low valence (in compounds with hydrogen and metals) must be determined by the following formula: 8 - group number;

The more you work with chemical elements, the better remember their valence. And for starters enough and such a Cribs:



Those elements whose valence is disturbed with pink color.

Valtility is the ability of atoms of some chemical elements to attach atoms of other elements. For successful writing formulas, the correct task solving is necessary to know well how to determine valence. First you need to learn all the elements with constant valence. Here they are: 1. Hydrogen, halogen, alkali metals (are always monovalent); 2. Oxygen and alkaline earth metals (bivalent); 3. B and Al (trivalent). To determine valence on the Mendeleev table , It is necessary to find out in which group there is a chemical element and determine, it is in the main group or side.

The element may have one or more valences.

The maximum valence of elements is equal to the number of valence electrons. We can define valence, knowing the location of the element in the periodic table. The maximum number of valence is equal to the number number in which the required element is located.

The valence is denoted by the Roman number and, as a rule, is written in the upper right corner of the element symbol.

Some elements may have different valence in different connections.

For example, sulfur has the following valence:

• II in connection H2S
• IV in connection SO2
• VI in connection SO3

The rules for determining valence is not as easy to use, therefore, you need to remember.

To determine the valence on the Mendeleev table simply. As a rule, it corresponds to the group number in which the element is located. But there are elements that can have different valence in different compounds. In this case, we are talking about constant and variable valence. A variable can be the maximum equal to the number of the group, and may be minimal or intermediate.

But it is much more interesting to determine valence in connections. For this there are a number of rules. First of all, it is easy to determine the valence of elements if one element in the compound has permanent valence, for example, oxygen or hydrogen. The restore agent is placed on the left, that is, an element with positive valence, on the right - an oxidizer, that is, an element with negative valence. The index of an element with constant valence is multiplied by this valence and is divided into an index of an element with an unknown valence.

Example: silicon oxides. Oxygen valence -2. We will find a silicon valence.

SiO 1 * 2/1 \u003d 2 Silicon valence in monoxide is +2.

SiO2 2 * 2/1 \u003d 4 Silicon valence in dioxide is +4.

Various chemical elements differ in their ability to create chemical bonds, that is, to connect to other atoms. Therefore, in complex substances they can only be in certain ratios. We will figure it out how to determine valence on the Mendeleev table.

There is such a definition of valence: this is the ability of an atom to form a certain number of chemical bonds. Unlike, this value is always only positive and denoted by Roman numbers.

As a unit, this characteristic for hydrogen is used, which is adopted equal to I. This property shows that this element can be connected with a number of monovalent atoms. For oxygen, this value is always equal to II.

To know this characteristic is necessary to correctly record the chemical formulas of substances and equations. Knowing this value will help to establish a relationship between the number of atoms of various types in the molecule.

This concept arose in chemistry in the XIX century. The beginning of the theory explaining the compound of atoms in various ratios, put Frankland, but his ideas about the "binding force" were not very common. A decisive role in the development of theory belonged to Kekule. He called the property to form a certain amount of links with basicity. Kekule believed that it is the fundamental and unchanged property of each type of atoms. Important additions to the theory made Butlers. With the development of this theory, it was possible to clearly depict molecules. It helped in the study of the structure of various substances.

What will the periodic table help?

You can find valence by looking at the group number in a short-range version. For most elements that this characteristic is constant (only one value takes), it coincides with the group number.

Such properties have the main subgroups. Why? The number of the group corresponds to the number of electrons on the outer shell. These electrons are called valence. They are responsible for the possibility of connecting to other atoms.

The group makes elements with a similar electronic shell device, and the kernel charge increases from top to bottom. In short-range form, each group is divided into the main and side subgroup. Representatives of the main subgroups are S and P-elements, representatives of side subgroups have electrons on D and F-orbitals.

How to determine the valence of chemical elements if it changes? It can coincide with the group number or equal to the number of minus eight group, as well as take other meanings.

Important! The higher the right item, the one to its property form the relationship less. What he is more shifted down and left, the more she is.

The way valence changes in the Mendeleev table for a specific type of atom depends on the structure of its electronic shell. Sulfur, for example, may be two-, four- and hexavalent.

Basically (unexcited) condition in sulfur, two unpaired electrons are on a paragraph 3r. In this state, it can be connected with two hydrogen atoms and form hydrogen sulfide. If the sulfur goes into a more excited state, then one electron will switch to a free 3D-sublevel, and unpaired electrons will become 4.

Sulfur will be pickled. If you tell it even more energy, then another electron will go with a 3s 3s sublevel. The sulfur will go to an even more excited state and will become hexavalent.

Permanent and variable

Sometimes the ability to form chemical bonds may change. It depends on which connection includes an element. For example, sulfur in the composition of H2S is bivalent, as part of SO2 - tetravalent, and in SO3 is hexavalent. The greatest of these values \u200b\u200bis called higher, and the smallest - lower. The highest and low valence on the Mendeleev table can be installed as follows: the highest coincides with the group number, and the lowest equals 8 minus group number.

How to determine the valence of chemical elements and then whether it changes? You need to install, we have a case with a metal or non-metallol. If it is metal, you need to install, it refers to the main or side subgroup.

• Metals have the main subgroups the ability to form chemical interrelations constant.
• Metals have side subgroups - variable.
• Nemetalles are also variable. In most cases, it takes two values \u200b\u200b- higher and lower, but sometimes there may be a greater number of options. Examples - sulfur, chlorine, bromine, iodine, chrome and others.

In compounds, the low valence shows the element that is above and the right in the periodic table, respectively, the highest one that is left below.

Often the ability to form chemical bonds takes more than two values. Then the table cannot be obtained, and you will need to learn. Examples of such substances:

• carbon;
• sulfur;
• chlorine;
• bromine.

How to determine the valence of the element in the compound formula? If it is known for other components of the substance, it is easy. For example, it is required to calculate this property for chlorine in NaCl. Sodium is the element of the main subgroup of the first group, so it is monovalent. Consequently, chlorine in this substance can also create only one connection and is also monovalent.

Important!However, it is not always possible to learn this property for all atoms in the complex substance. For example, we take HCLO4. Knowing the properties of hydrogen, you can only establish that CLO4 is a monovalent residue.

How else to know this magnitude?

The ability to form a certain number of connections does not always coincide with the number of the group, and in some cases it will be necessary to just memorize. A table of valence of chemical elements will come to the rescue, where the values \u200b\u200bof this value are given. In the chemistry textbook for grade 8, the values \u200b\u200bof the ability to connect to other atoms of the most common types of atoms are given.

Application

It is worth saying that chemist scientists. Currently, the concept of valence on the Mendeleev table is almost not used. Instead of it for the ability of a substance to form a certain number of relationships, the concept of oxidation is used for substances with the structure - covalency, and for the substances of the ion structure - the charge of the ion.

However, the concept under consideration is used for methodical purposes. With it, it is easy to explain why atoms different species They are connected in the ratios that we observe and why these relations for different compounds are different.

At the moment, the approach, according to which the connection of elements into new substances has always been explained by valence on the Mendeleev table, regardless of the type of communication in the compound, is outdated. Now we know that for ionic, covalent, metallic bonds, there are different mechanisms for combining atoms into the molecule.

Useful video

Let's summarize

On the Mendeleev table, it is possible to determine the ability to form chemical bonds for all elements. For those that manifest one valence on the Mendeleev table, it is in most cases equal to the group number. If there are two variants of this value, it can be equal to the group number or eight minus group number. There are also special tables for which this characteristic can be found.