The first stone of the stumbling block studying chemistry. A big mistake is an approach when the student is not trying to understand the valence, waiting for the knowledge about this then will be applied by themselves. But this approach is incorrect, since without understanding this we rest in the deadlock of the inability to draw up even the simplest formula.

What is "valence" of elements?

Valence is a word taken by scientists from the Latin language, which means strength and possibility. Of course, the name is no coincidence and can help us very much in understanding the essence of the term. After all, valence characterizes an atom from the point of view of its ability to form connections with other atoms. Speaking otherwise, the valence can be viewed as an impact of an atom to form connections, thanks to which molecules appear.

Denote valuation of element Always only Roman numbers. It is possible to see its value for different atoms in a special table.

What are the characteristics of the valence of elements?

All substances that possess valence are characterized by the fact that they have or constant (in all connections), or variable. Permanent valence is a characteristic of a very small group of substances (hydrogen, fluorine, sodium, potassium, oxygen, etc. much larger in the world of atoms that have a variable valence. In different reactions, interacting with different atoms, they become amented. For example, nitrogen in connection NH3 has valence - III, as it is associated with three atoms, and in nature it happens with valence from one to four. I repeat once again that different valences are a more common phenomenon.

The influence of the valence of elements in chemical reactions.

Even how scientists learned that the atom is not the smallest particle in the world, they have already operated on this concept. They understood that there is an internal factor that affects the flow of a chemical reaction of various substances. Due to the fact that scientists have seen the structure of the molecule in different ways, the concept of " valuation of element"Survived several metamorphosis.

The valence of the substance is determined by the amount of external electrons of the atom. What is the number of electrons at the atom, it is capable of making so much compounds. Thus, the "valence" implies the number of electronic pairs of atoms.

Although the electronic theory appeared much later, after the "separation" of an atom into smaller particles, before that scientists still quite successfully determined valence in most cases. It was possible to them thanks to the chemical analysis of substances.

It was hard work: first of all, it was necessary to determine the mass of the element in its pure form. Next, with the help of chemical analysis, scientists determined what the composition of the compound, and only then could calculate how many atoms contains a substance molecule.

This method is still used, but is not universal. So it is convenient to determine the element in a simple compound of substances. For example, with monovalent hydrogen, or bivalent oxygen.

But when working with acids, the method is not particularly successful. No, we can partially use it, for example, when determining the valence of compounds of acid residues.

It looks like this: Using the knowledge that the oxygen valence is always equal to two, we can easily calculate the valence of the whole acid residue. For example, in H 2 SO 3, the SO 3 - I valence, in HCLO 3, Valuation CLO 3 - I.

Valuation of elements in formulas.

As we said above, the concept " valuation of elements»Connected an electronic structure of an atom. But this is not the only type of communication that exist in nature. Chemists are familiar with ion, crystalline and other forms of the structure of the substance. For such structures, the valence is no longer so relevant, but working with molecular reaction formulas, we must take it into account.

In order to make the formula, we must arrange all the indices that balance the number of atoms entering into the reaction. Only knowing the valence of substances, we can properly arrange indexes. Conversely, knowing the molecular formula and having indices, you can find out the valence of elements, which are part of the substance.

It is important for the product of such calculations to remember that the valence of both elements that have entered into the reaction will be equal, and therefore, it is necessary to find the smallest common to search.

For example, take, iron oxide. In the chemical bond, we participate iron and oxygen. In this reaction in iron, the valence is equal to III, and oxygen - II. By easy calculations, we determine that the smallest total multiple - 6. And therefore the formula has the form of Fe 2 O 3.

Unusual ways to determine the valence of elements.

There are more non-standard but interesting methods Definition of valence of substance. If you know well the properties of the element, then you can even visually determine the valence. For example, copper. Its oxides will be red and black, and hydroxides are yellow and blue.

Visuality.

In order to valuation of elementit was more clearly recommended to write structural formulas. Creating them, we write the conditional designations of atoms, and then draw dashes, relying on valence. There, every shortcut denotes each of the elements and it turns out very clearly.

Table Dmitry Ivanovich Mendeleev is a multifunctional reference material for which it is permitted to learn the most necessary data on chemical elements. The most basic is to know the basic theses of her "reading", that is, it is necessary to be able to positively use this information material, which will serve as a beautiful help to solve any tasks in chemistry. The greater that the table is permitted on all types of control of knowledge, including even the exam.

You will need

• Table D.I. Imeleeva, pen, paper

Instruction

1. The table is a design in which chemical elements are located in their own theses and laws. That is, it is allowed to say that the table is a multi-storey "house", in which the chemical elements "live", and all of them have their own apartment under a certain number. The horizontals are located "floors" - periods that can be small and huge. If the period consists of 2 rows (which is indicated on the side of the numbering), then such a period is called huge. If he has only one row, it is called small.

2. Also, the table is divided into "entrances" - groups that each eight. As in any entrance of the apartment are on the left and right, so and here the chemical elements are located along the same thesis. Only in this embodiment, their placement is uneven - on the one hand, great elements and then they talk about the main group, with another - smaller and this indicates that the group side.

3. Valence is the ability of elements to form chemical connections. There is a valence of a continuous, which does not change and variable having a different value depending on whether the element is included in the composition of which substance. When determining valence according to the Mendeleev table, you need to pay attention to such words: group number elements and its type (that is, the main either side group). Continuous valence in this case is determined by the number of the group of the main subgroup. In order to find out the value of the valence variable (if there is such, and traditionally in non-metals), then it is necessary from 8 (each 8 groups - the subset of such a figure) subtracting the number of the group in which the element is located.

4. Example # 1. If you look at the elements of the first group of the main subgroup (alkali metals), then allowed to draw the result that they all have a valence equal to I (Li, Na, K, Rb, CS, FR).

5. Example No. 2. Elements of the 2nd group of the main subgroup (alkaline-land metals) respectively have valence II (BE, MG, CA, SR, BA, RA).

6. Example number 3. If we talk about nonmetallah, then let's say p (phosphorus) is in the group of the main subgroup. The subset of his valence will be equal to V. In addition, phosphorus has another valence value, and for its definition, it is necessary to perform an action 8 - element number. So, 8 - 5 (the number of the phosphorus group) \u003d 3. Incidentally, the second valence of phosphorus is equal to III.

7. Example number 4. Halogens are in the VII group of the main subgroup. It means that their valence will be equal to VII. However, considering that it is non-metals, it is necessary to make an arithmetic effect: 8 - 7 (number of element group) \u003d 1. Incidentally, the other valence of halogens is equal to I.

8. For elements of side subgroups (and they include only metals) valence needs to be memorized, the greater that in most cases it is equal to I, II, less often III. Also necessary to memorize valence chemical elementswhich have more than 2 values.

From school or even before all knows, everything around, including ourselves, consists of their atoms - the smallest and indivisible particles. Due to the ability of atoms to connect with each other, the variety of our world is enormous. The ability of this chemical atoms element to form connections with other atoms called valence element .

Instruction

1. The representation of valence was included in the chemistry in the nineteenth century, then the valence of the hydrogen atom was adopted for its unit. Valentidity of other element It can be defined as the number of hydrogen atoms, which joins one atom of a different substance. Similarly, the valence of hydrogen is determined by the oxygen valence, which is found, is equal to two and, therefore, it allows you to determine the valence of other elements in compounds with oxygen with simple arithmetic actions. Valence element Oxygen is equal to the double number of oxygen atoms, which can attach one atom of this element .

2. To determine valence element allowed to use and formula. Premisto that there is a certain ratio between valence element , its equivalent mass and molar mass of its atoms. The relationship between these qualities is expressed by the formula: valence \u003d molar mass of atoms / equivalent weight. Because the equivalent mass is the number that needs to be replaced by one praying of hydrogen or for reaction with one pitch of hydrogen, the greater the molar mass in comparison with the mass is equivalent, the greater the number of hydrogen atoms can be replaced or attached to atom element So, the higher the valence.

3. Communication between chemical element Mi has different nature. It may be covalent bond, ionic, metal. For the formation of the connection atom, it is necessary to have: an electric charge, an unpaired valence electron, a free valence orbital or a watelling couple of valence electrons. Together, these features determine the valence condition and valence abilities of the atom.

4. Knowing the number of an atom electrons, which is equal to the ordinal number element In the periodic system of elements, guided by the theses of the lowest energy, the thesis of Pauli and the Rule of Hinda is allowed to build an electronic configuration of the atom. These constructions will be allowed to analyze the valence probabilities of the atom. In all cases, it is primarily that there are probabilities to form connections due to the presence of unpaired valence electrons, additional valence abilities, such as free orbital or a different pair of valence electrons, can remain unrealized if it is unsatisfactory energy. And each of the foregoing is allowed to make the result that It is easier to determine the valence of an atom in some compound, and it is much more difficult to find out the valence abilities of atoms. However, practice will make it easy and this.

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Tip 3: How to determine the valence of chemical elements

Valence The chemical element is the ability of an atom to attach or replace a certain number of other atoms or nuclear groups with the formation of a chemical bond. It must be remembered that some atoms of the same chemical element may have different valences in various connections.

You will need

• mendeleev table

Instruction

1. Hydrogen and oxygen are considered monovalent and bivalent elements, respectively. The measure of valence is the number of hydrogen atoms or oxygen, which the element connects to the formation of hydride or oxide. Let X be an element whose valence needs to be determined. Then Xhn is the hydride of this element, and Xmon is its oxide. Example: Ammonia formula - NH3, here in nitrogen valence 3. Sodium is monovalent in compound Na2O.

2. To determine the valence of the element, it is necessary to multiply the number of hydrogen atoms or oxygen in the compound on the valence of hydrogen and oxygen, respectively, and then divided by the number of atoms of the chemical element, whose valence is located.

3. Valence The element can also be determined by other atoms with valence. In different compounds, atoms of the same element may exhibit different valence. For example, sulfur is bivalent in H2S and CUS connections, four and SF4 connections are hexavalent in SO3 and SF6 connections.

4. The maximum valence of the element is considered to be equal to the number of electrons in the outer electron sheath of the atom. Maximum valence elements The same group of the periodic system usually corresponds to its sequence number. For instance, maximum valence The carbon atom C should be equal to 4.

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For schoolchildren comprehension table Mendeleev - Horrible sleep. Even thirty-six elements that are usually asked teachers, turn around the tedious couch and headache. Many do not even believe that learn table Mendeleev really. But the use of mnemotechnics can make it much easy to easily ease the life of Scholars.

Instruction

1. To understand theory and prefer the necessary technical plant that facilitates the storage of the material is called mnemonic. Their main trick is the creation of associative connections when abstract information is packaged in a bright picture, sound or even smell. There are several mnemonic techniques. Let's say it is allowed to write a story from the elements of memorized information, search for consonant words (Rubidium - the chopper, cesium - Julius Caesar), include the spatial imagination or it is easy to sort the elements of the periodic table of Mendeleev.

2. Ballad about azoteriform elements of the periodic table of Mendeleev are excellent with meaning, according to certain signs: for valence, let's say. So, alkali metals are rhymes at a duct easily and sound like a song: "Lithium, potassium, sodium, rubidium, cesium France." "Magnesium, calcium, zinc and barium are their valence equal to the pair" - the unfavorable classic of school folklore. On the same topic: "Sodium, Potassium, Silver - monovalent good-naturedly" and "sodium, potassium and argenum are forever monstant." Creation in the distinction from the cavity, which is enough for a couple of days for a couple of days, stimulates long-term memory. So, more than a lot of fairy tales about aluminum, poems about nitrogen and songs about valence - and memorization will go like oil.

3. Acid thrillerlde of memorization simplification is invented by a story in which the elements of the Mendeleev table turn into heroes, the parties of the landscape or plot elements. Here, let's say, each famous text: "Asian (nitrogen) began to pour (lithium) water (hydrogen) in the pine forest (boron). But not he (neon) was needed us, but Magnolia (Magnesium). " It is allowed to supplement the story about Ferrari (Steel - Ferrum), in which the secret spy "Chlorine Zero Seventeen" (17 - the sequence number of chlorine), in order to catch the maniac arseny (arsenic - arsenicum), who had 33 tooth (33 - sequence number Arsenic), but suddenly something sour fell into his mouth (oxygen), it was eight poisoned bullets (8 - sequence number of oxygen) ... continue allowed to infinity. By the way, the novel, written by the Mendeleev table, is allowed to attach the literature teacher as an experimental text. She will probably like it.

4. Early the memory castle is one of the items of fairly effective memorization technique when spatial thinking is included. The secret of her is that we can easily describe our room or the path from home to the store, school, institute. In order to remember the sequence of elements, it is necessary to put them on the road (either in the room), and to present every element of the income clear, visibly, noticeable. Here hydrogen is a thin blonde with an elongated face. Harman, the one that puts the tile - silicon. A group of nobles in a precious car is an inert gases. And, of course, the seller of balloons - helium.

Note!
It is not necessary to force yourself to remember information on cards. The best link the whole element with some brilliant way. Silicon - with a silicon valley. Lithium - with lithium batteries in a mobile phone. Options may be a lot. But the combination of visual image, mechanical memorization, tactile sensation from rough or, on the contrary, a smooth glossy card will help to easily raise the most smallest details from the subsoil of memory.

Helpful advice
It is permitted to draw the same cards with information about the elements, as was at one time from Mendeleev, but only to supplement them with current information: the number of electrons on the external tier, let's say. All that is needed is to lay them before bedtime.

Chemistry for every schoolchildo begins with the Mendeleev table and fundamental laws. And closer only later, looking for himself, which will comprehend this difficult science, is allowed to begin the preparation of chemical formulas. For competent connection of the connection you need to know valence Atoms constituting it.

Instruction

1. Valence is the ability of one atoms to hold near themselves a certain number of others and it is expressed by the number of atoms held. That is, the more powerful item, the more like he valence .

2. For example, it is allowed to apply two substances - HCl and H2O. It is cool to each hydrochloric acid and water. The first substance contains one hydrogen atom (H) and one chlorine atom (CL). This suggests that in this compound they form one connection, that is, one atom is held near him. Consequently valence And one, and other equal to 1. It is also easy to determine valence The elements constituting the water molecule. It contains two hydrogen atoms and one oxygen atom. Incidentally, the oxygen atom formed two ties to attach 2 hydrogen, and they, in turn, by one connection. It means valence Oxygen is 2, and hydrogen - 1.

3. But occasionally communicates with substances Mu more difficult in structure and properties of the components of their atoms. There are two types of elements: with continuous (oxygen, hydrogen, etc.) and non-permanent valence Yu. At the second type atoms, this number depends on the compound, which they enter. As an example, it is permitted to bring sulfur (S). It can have valence 2, 4, 6 and occasionally even 8. Determine the ability of elements such as sulfur, keeping around atoms, more difficult. To do this, you need to know the properties of other components. substances .

4. Remember the rule: a product of the number of atoms on valence One element in the connection should coincide with the same product for another element. This is allowed to check again by contacting the water molecule (H2O): 2 (the number of hydrogen) * 1 (its valence) \u003d 21 (oxygen number) * 2 (it valence) \u003d 22 \u003d 2 - it means everything is determined correctly.

5. Now check this algorithm for more difficult substance, say, N2O5 - nitrogen oxide. Previously indicated that oxygen has a continuous valence 2, it is decided to make an equation: 2 ( valence oxygen) * 5 (its number) \u003d x (unknown valence nitrogen) * 2 (its number) by simple arithmetic calculations is allowed to determine that valence Nitrogen as part of this compound is 5.

Valence - This is the ability of chemical elements to keep a certain number of atoms of other elements. At the same time, this is the number of connections formed by this atom with other atoms. Determine valence pretty primitively.

Instruction

1. Take note that the rate of valence Roman numbers is indicated and put on the element sign.

2. Please note: if the formula of the two-element substance is written correctly, then, when multiplying the number of atoms of any element on its valence, all element will turn out to be identical works.

3. Please note that the valence of atoms of some elements is continuous, and others are changed, that is, it has the quality to change. For example, hydrogen in all connections is monovalent, from the fact that only one connection is formed. Oxygen Molds to form two bonds, while being bivalent. But the sulfur valence may be II, IV or VI. It all depends on the element with which it connects. Thus, sulfur is an element with variable valence.

4. Notify that in the molecules of hydrogen compounds to calculate the valence of the inuceive primitively. Hydrogen is invariably monovalent, and this indicator in the element associated with it will be equal to the number of hydrogen atoms in this molecule. For example, in Cah2 calcium will be bivalent.

5. Remember the basic rule of the definition of valence: the product of the index of the valence of the atom of some element and the number of its atoms in some molecule is invariably equal to the product of the valence indicator of the atom of the second element and the number of its atoms in this molecule.

6. Look at the alphabetic formula denoting this equality: V1 x K1 \u003d V2 x K2, where V is the valence of the atoms of the elements, and K is the number of atoms in the molecule. With its imaginary, it is easy to determine the valence indicator of any element if the remaining data is carried out.

7. Imagine an example with sulfur oxide molecule SO2. Oxygen in all compounds is bivalent, consequently, substituting the values \u200b\u200bin the proportion: Vcslorod x oxygen \u003d VCERS X Xers, we obtain: 2 x 2 \u003d VCERs x 2. From here VSERS \u003d 4/2 \u003d 2. Thus, the sulfur valence in this molecule is equal to 2.

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Opening of the Periodic Law and the creation of an ordered system of chemical elements D.I. Mendeleev became an apogee of becoming chemistry in the XIX century. Scientists were summarized and classified extensive material skills on the properties of elements.

Instruction

1. In the XIX century there were no ideas about the structure of the atom. Opening D.I. Mendeleev was only a generalization of experienced facts, but their physical sense remained incomprehensible. When the first data on the structure of the kernel and the separation of electrons in atoms occurred, it was allowed to take a look at the periodic law and the system of elements anemone. Table D.I. Mendeleev gives a chance to visually trace the frequency of properties of elements found in nature.

2. Any element in the table assigned a certain sequence number (H - 1, Li - 2, BE - 3, etc.). This number corresponds to the chore charge (the number of protons in the core) and the number of electrons rotating around the kernel. The number of protons is thus equal to the number of electrons, and this suggests that ordinary conditions The atom is electrically neutral.

3. The division of seven periods is due to the number of energy tiers of an atom. Atoms of the first period have a single-level electronic shell, the second - two-level, third - three-level, etc. When filling out the new energy tier, the newest period begins.

4. The first elements of each period are characterized by atoms having one electron on an external tier, it is alkali metal atoms. Periods are completed by atoms of decent gas, having an external energy tier fully filled with electrons: in the first period, the inert gases have 2 electrons, in subsequent - 8. It is because of the similar structure of the electronic shells of a group of elements that have similar physicochemical properties.

5. Table D.I. Mendeleev is present 8 major subgroups. This number is due to the maximum allowable number of electrons on the energy tier.

6. At the bottom of the periodic system, lanthanoids and actinoids are highlighted as independent rows.

7. With the support of the Table D.I. Mendeleeva is allowed to observe the frequency of the following properties of the elements: the radius of the atom, the volume of the atom; the potential of ionization; Electron affinity forces; Electricity atom; degree of oxidation; physical properties of possible compounds.

8. For example, atom radii, if you look through the period, decrease left to right; Grow down from top to bottom, if you look through the group.

9. Clearly traceable frequency of elements in Table D.I. Mendeleev is meaningfully explained by the consistent temper of the filling by electrons of energy tiers.

Periodic law, which is the basis of the current chemistry and explaining the validity of the metamorphosis of the properties of chemical elements, DI was opened. Mendeleev in 1869. The physical sense of this law is revealed by comprehending the difficult structure of the atom.

In the XIX century it was believed that nuclear mass is the main poles of the element, it was investigating that it was used to systematize substances. Now atoms are determined and identified by the magnitude of the charge of their kernel (the number of protons and the sequence number in the Mendeleev table). However, the nuclear mass of elements for some exceptions (let's say, the nuclear mass of potassium is less than the nuclear mass of argon) increases commensurately their kernel charge. In an increase in the nuclear mass, periodic metamorphosis of the properties of elements and their connections is monitored. This is the metallicity and non-metallium atoms, nuclear radius and volume, ionization potential, electron affinity, electronegativity, oxidation degree, physical properties compounds (boiling, melting, density), basic, amphoteriness or acidity.

How many elements in the current Mendeleev table

The Mendeleev table graphically expresses its open periodic law. The current periodic system contains 112 chemical elements (the latter - recesses, Darmstadtion, Rentgments and Copernation). According to the latest data, the following 8 elements are open (up to 120 inclusive), but not all of them have received their names, and these elements are still a few more printed editions. There is a certain cell in the periodic system and has its own sequence number, The corresponding charge of the kernel of its atom.

How to build a periodic system

The structure of the periodic system is represented by seven periods, ten rows and eight groups. The entire period begins with an alkaline metal and ends with a decent gas. Exceptions are 1st period, beginning with hydrogen, and the seventh unfinished period. Periods are divided into small and huge. Small periods (1st, 2nd, 3rd) consist of one horizontal row, huge (fourth, fifth, sixth) - from 2 horizontal series. The upper rows in huge periods are called even, the lower - odd. In the sixth period of the table, later Lanthan (sequence number 57) contains 14 elements similar to the properties for Lantane - Lantanoids. They are put into the lower part of the table with a separate line. The same applies to actinoids, located later action (with number 89) and in many respects repetitive properties. The following groups of large periods (4, 6, 8, 10) are filled with metals only. The elements in groups exhibit identical higher valences in oxides and other connections, and this valence corresponds to the group number. The main subgroups contain elements of small and large periods, side - only large. From top to bottom, metal properties are enhanced, non-metallic - weaken. All atoms of side subgroups are metals.

Tip 9: Selenium as a chemical element of the Mendeleev table

The chemical element is selenged to the VI group of the periodic Mendeleev system, it is a chalcogen. Natural selenium consists of six stable isotopes. Vastimo also 16 radioactive isotopes selenium.

Instruction

1. The selenium is considered a somewhat rare and scattered element, in the biosphere he actively migrates, forming more than 50 minerals. The most famous of them are: bercelianit, naughty, native selenium and chalcomat.

2. Selenium is contained in volcanic sulfur, galena, pyrite, bismutin and other sulphides. It is extracted from lead, copper, nickel and other ores in which it is in a scattered state.

3. In the tissues of most living beings, it is contained from 0.001 to 1 mg / kg of selenium, some plants, marine organisms and mushrooms are concentrated. For a row of plants selenium is the desired element. The need for man and beasts in the Selena is 50-100 μg / kg of food, this element owns antioxidant properties, affects the ayum of enzymatic reactions and increases the sensitivity of the retina to the light.

4. Selenium may exist in different allotropic modifications: amorphous (vitreous, powdered and colloidated selenium), as well as crystalline. When corrected selenium from the solution of selenium acid or the rapid cooling of its vapor is obtained by amorphous scarlet powdered and colloidal selenium.

5. When heated, all modifications of this chemical element above 220 ° C and further cooling is formed by glassy selenium, it is fragile and owns a glass glitter.

6. Particularly resistant thermally hexagonal gray selenium, the grill of which is built from the spiral chains of atoms located in parallel to each other. It is obtained by heating other forms of selenium to melting and leisurely cooling to 180-210 ° C. Inside the chains of hexagonal selenium atoms are associated covalently.

7. Seleni is stable in air, it does not act on it: oxygen, water, diluted sulfur and hydrochloric acid, however, it is canceled dissolved in nitric acid. Interacting with metals, selenium forms selenides. It is famous for the village of complex compounds Selena, all of them are poisonous.

8. Get selenium from waste paper or sulfate production, the method of electrolytic refining copper. In the sludge, this element is present in conjunction with heavy and decent metals, gray and tellurium. To remove it, the slots are filtered, after that heated with concentrated sulfuric acid or subjected to oxidative firing at a temperature of 700 ° C.

9. Selenium is used in the production of rectifying semiconductor diodes and other converter techniques. In metallurgy with its support, the fine-grained construction is given, and also improve its mechanical properties. In the chemical industry selenium used as a catalyst.

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Note!
Be careful when determining metals and non-metals. For this, traditionally in the table is given notation.

Element;
\u003e predict the possible values \u200b\u200bof the element valence, based on its placement in the periodic system;
\u003e determine the values \u200b\u200bof the valence of elements in binary compounds according to their formulas;
\u003e Make formulas of binary compounds, based on the values \u200b\u200bof the valence of elements.

The value of the valence of the element, if necessary, indicate in the chemical formula of the Roman number above its symbol: in mathematical calculations and the text it uses Arabic figures.

Determine the valence of elements in the ammonia molecules NH 3 and methane CH 4.

Information on the valence of elements in the substance can be represented in another way. First, they are recorded at a certain distance from each other, the characters of each atom located in the molecule. The monovalent atom is then connected to another single dash, two twisters are carried out from a bivalent atom, and so on.:

Such formulas are called graphic. They show the order of connecting atoms in molecules.

A simple hydrogen substance molecule has a graphic the H-H formula. The graphic formulas of fluorine, chlorine, bromine, iodine molecules are similar. Graphic formula of oxygen molecules 0 \u003d 0, and molecules Nitrogen.

By constiting such formulas for molecules of complex substances, it should be borne in mind that the atoms of one element are usually not interconnected.

Picture graphic formulas of ammonia and methane molecules.

From the graphical formula of the molecule easily determine the valence of each atom. The value of valence is equal to the amount of drops that come from the atom.

For compounds of the ionic and atomic structure, graphic formulas are not used.

Valuation of the element and its placement in the periodic system.

Some elements have permanent valence.

It is interesting

At the beginning of the XIX century. In the views on the composition of chemical compounds dominated
the principle of "the greatest simplicity". Thus, the formula of the water was recorded HO, and not H 2 O.

Hydrogen and fluor are always monovalent, and Oksigen - bivalent. Other elements with permanent valence are located in the I-III groups of the periodic system, and the value of the valence of each element coincides with the group number. Thus, the element I of the group of lithium is monovalent, the element II of the group of magnesium is bivalent, and the element III of the boron group is trivalent. Exceptions are the elements I of the group of dumplings (the values \u200b\u200bof valence - I and 2) and Aurum (I and 3).

Most elements have a variable valence. Create its values \u200b\u200bfor some of them:

Plumbum (IV Group) - 2.4;
Phosphorus (V group) - 3.5;
Chromium (VI group) - 2, 3, 6;
Sulfur (VI group) - 2, 4, 6;
Mangan (VII group) - 2, 4, 6, 7;
Chlorine (VII Group) - I, 3, 5, 7.

From these information flows an important rule: The maximum value of the valence of the element coincides with the number of the group in which it is 1. Since B. periodic system Eight groups, the values \u200b\u200bof the valence of elements can be from i to 8.

There is another rule: the value of the valence of the non-metallic element in a compound with the hydrogen or with a metal element is 8 minus the group number in which the element is placed. I confirm it with examples of compounds of elements with hydrogen. Element VII of the iodine group in the hydrogen-breed Hi is monovalent (8-7 \u003d 1), element Vi of the group of hydroxygen in water H 2 o bivalent (8 - 6 \u003d 2), element V nitrogen group in ammonia
NH3 trivalent (8 - 5 \u003d 3).

Determination of the valence of elements in the binary compound according to its formula.

Binary 2 is a compound formed by two elements.

1 There are several exceptions.
2 The term comes from the Latin word binarius - double; Consisting of two parts.

It is interesting

The compounds formed by three or more elements are different.

Find out the value of the valence of the element in the compound when the element has a variable valence. How do it perform the task We will show on the example.

Find the value of the valence of the iodine in its compound with the hydroxygen, which has formula I 2 O 5.

You know that oxigen is a bivalent element. We write the value of its valence over the symbol of this element in the chemical compound formula :. At 5 oxygen atoms account for 2 * 5 \u003d 10 units of valence. They need to "distribute" between two iodine atoms (10: 2 \u003d 5). It follows from this that the iodine in the compound is fivewalenten.

The formula of the compound with the designation of the valence of elements -

Determine the valence of elements in compounds with CO 2 and Cl 2 O 7 formulas.

Drawing up the chemical formulas for the valence of elements.

We will perform the task opposite to the previous one, be the chemical formula of the sulfur compound with the oxygen, in which Sulfur is hexavalenten.

First, write the symbols of the elements forming the connection, and indicate the valence values \u200b\u200babove them :. Then we find the smallest number, which is divided without a balance on both valence values. This is a number 6. We divide it on the value of the valence of each element and we obtain the appropriate indexes in the chemical compound formula: .

To verify the chemical formula, the rule is used: the products of the valence values \u200b\u200bof each element by the number of its atoms in the formula are the same. These works for the newly derived chemical formula: 6 -1 \u003d 2-3.

Remember that in the formulas of the compounds, including binary, first write characters metal elementsAnd then - non-metallic. If the connection is formed only by non-metallic elements and among them there is an oxygen or fluor, then these elements are recorded by the latter.

It is interesting

The procedure for recording items in the formula of the oxygen compound with fluor is: of 2.

Make the chemical formulas of boron compounds with fluor and oxygen.

The reasons for the compound of atoms with each other and the explanation of the values \u200b\u200bof the valence of elements are associated with the structure of atoms. This material will be considered in grade 8.

conclusions

Valence is the ability of an atom to connect to a certain number of the same or other atoms.

There are elements with a constant and variable valence. Hydrogen and fluor are always monovalent, hydroxygen - duvelanet.

The valence values \u200b\u200bof the elements are reflected in the graphic formulas of molecules with the corresponding number of drops near atoms.

The products of the values \u200b\u200bof the valence of each element by the amount of its atoms in the binary connection formula are the same.

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75. What is valence? Name the maximum and minimum valence of chemical elements.

76. Specify the characters of elements having a constant valence: K, Ca, Cu, Cl, Zn, F, N.

77. Determine the valence of all elements in the compounds that have such formulas:

78. Determine the valence of elements in compounds with such formulas:
a) Bah 2, V 2 O 5, MOS 3, SIF 4, LI 3 P; b) Cus, Tici 4, Ca 3 N 2, P 2 O 3, Mn 2 O 7.

79. Make the compounds formed by elements with constant valence: Na ... H ..., Ba ... F ..., Al ... o ..., ai ... f ....

80. Make the compound formulas using the specified valence of some items:

81. Write the formulas of compounds with the oxygen of such elements: a) lithium; b) magnesium; c) Osmia (exhibits valence 4 and 8).

82. Picture graphic formulas Ci 2 O molecules, pH 3, SO 3.

83. Determine the valence of elements by graphic formulas of molecules:

At leisure

"Construct" molecules

Fig. 45. Model Molecule Methane CH 4

According to graphic formulas, models of molecules can be made (Fig. 45). The most comfortable material for this is plasticine. From it makes balliaciatomes (for atoms of various elements, plasticine of different colors are used). Balls are connected using matches; Each match replaces one dash in the graphic formula of the molecule.

Make models of H 2 molecules, O 2, H 2 O (has angular shape), NH3 (has a pyramid shape), CO 2 (has a linear form).

In order to learn how to make chemical formulas, it is necessary to find out the patterns according to which the atoms of chemical elements are connected between themselves in certain ratios. To do this, we compare the qualitative and quantitative composition of the compounds, the formulas of which HCl, H 2 O, NH 3, CH 4 (Fig. 12.1)

In terms of quality composition, these substances are similar: the composition of each of the molecules includes hydrogen atoms. Nevertheless, their quantitative composition of unequal. Chlorine, oxygen atoms, nitrogen, carbon are connected respectively with one, two, three and four hydrogen atoms

This pattern was noticed at the beginning of the XI century. J. Dalton. Over time I. Ya. Britzelius found that the largest number of atoms connected to the chemical element atom does not exceed a certain amount. In 1858, E. Frankland called the "connecting force" the ability of atoms to bind or replace a certain number of other atoms. "valence" (from lat. valentia - "Strength") offered in 1868 German chemist K. G. Vikhelhauses.

Valence - General property of atoms. It characterizes the ability of atoms of chemically (valence si-lami) to interact with each other.

The valence of many chemical elements was determined on the basis of experimental data on the quantitative and qualitative composition of substances. Per unit valenceif the valence of hydrogen is adopted. If an atom of a chemist element is connected to two monovalent atoms, then its valence is two. If it is connected to three monovalent atoms, it is trivalent and so on.

The highest value of the valence of chemical elements - VIII .

Valence is denoted by Roman numbers. Denote valence in the formulas of the compounds considered:

Also, scientists found that many elements in different compounds show different values \u200b\u200bof valence. That is, there are chemical elements with a constant and variable valence.

Is it possible to determine the valence on the position of the chest element in the periodic system? The maximum value of the element's valence coincides with the number of the periodic system group in which it is placed. Nevertheless, there are exceptions - nitrogen, oxygen, fluorine, copper and some other elements. Remember: The number of the group is indicated by the Roman number over the corresponding vertical column of the periodic system.

On this page, material on the themes:

Often people hear the word "valence", not fully understanding what it is. So what is valence? Valency is one of the terms that are used in the chemical structure. Valence, in fact, determines the possibility of an atom to form chemical bonds. Quantitatively valence is the number of connections in which an atom participates.

What is the valence of the element

Valence is an indicator of an atom ability to attach other atoms by forming with them inside the molecule, chemical bonds. The number of atom bonds is equal to the number of its unpaired electrons. These relationships are called covalent.

The unpaired electron is a free electron on the outer shell of an atom, which is connected to a pair with an outer electron of a different atom. Each pair of such electrons is called "electronic", and each of the electrons is valence. So the definition of the word "valence" is the amount of electronic pairs, with which one atom is associated with another atom.

Valence schematically can be depicted in structural chemical formulas. When it is not necessary, use simple formulas, where the valence is not specified.

The maximum valence of chemical elements from one group of the periodic Mendeleev system is equal to the sequence number of this group. Atoms of the same element may have different valence in different chemical compounds. The polarity of covalent bonds, which are formed, is not taken into account. That is why valence does not have a sign. Also, the valence cannot be a negative value and equal to zero.

Sometimes the concept of "valence" is equal to the concept of "oxidation", but this is not the case, although sometimes these indicators really coincide. The degree of oxidation is a formal term that means a possible charge that would receive an atom if its electronic pairs would move to an electrically negative atoms. Here the degree of oxidation can have some sign and expressed in charge units. This term is distributed in inorganic chemistry, because in inorganic compounds it is difficult to judge valence. And, on the contrary, valence uses in organic chemistry, because the molecular structure has a majority of organic compounds.

Now you know what the valence of chemical elements is!