The concept of the radius of the atom and the electronegativity of elements, their dependence on the arrangement of elements in the periodic table

Consider the relationship between the position of elements in the periodic table and such properties chemical elements, as atomic radius and electronegativity.

Atomic radius is a quantity that indicates the size of the electron shell of an atom. This is a very important quantity on which the properties of atoms of chemical elements depend. In the main subgroups, with an increase in the charge of the atomic nucleus, an increase in the number of electronic levels occurs, therefore the atomic radius increases with an increase in the ordinal number in the main subgroups. In periods, an increase in the charge of the nucleus of an atom of a chemical element occurs, which leads to an increase in the attraction of external electrons to the nucleus. In addition, with an increase in the nuclear charge, the number of electrons in the external level increases, but the number of electronic levels does not increase. These regularities lead to the compression of the electron shell around the nucleus. Therefore, the atomic radius decreases with increasing serial number in periods.

For example, let's arrange the chemical elements O, C, Li, F, N in the order of decreasing atomic radii. The listed chemical elements are in the second period. In the period, the atomic radii decrease with increasing serial number. Therefore, these chemical elements must be written in ascending order of their serial numbers: Li, C, N, O, F.

The properties of the elements and the substances formed by them depend on the number of valence electrons, equal to the group number in the periodic table.

Completed energy levels, as well as the outer level, contains eight electrons, have increased stability. This explains the chemical inertness of helium, neon and argon: they do not enter into chemical reactions at all. The atoms of all other chemical elements tend to give or attach electrons so that their electronic shell is stable, while they turn into charged particles.

Electronegativity - This is the ability of an atom in a compound to attract valence electrons to itself, i.e. electrons, through which chemical bonds between atoms are formed. This property is due to the fact that atoms tend to complete the outer electron layer and obtain an energetically favorable configuration of an inert gas - 8 electrons. Electronegativity depends on the ability of the atomic nucleus to attract electrons to the external energy level. The stronger this attraction, the more electronegativity. The force of attraction of electrons of the external energy level is the greater, the smaller the atomic radius. Consequently, the change in electronegativity in periods and major subgroups will be the opposite of a change in atomic radii. Therefore, in the main subgroups, electronegativity decreases with increasing serial number. In periods with increasing serial number, electronegativity increases.

For example, let's arrange the chemical elements Br, F, I, Cl in the order of increasing electronegativities. The listed chemical elements are in the main subgroup of the seventh group. In the main subgroups, with an increase in the electronegativity of the ordinal number, it decreases. Consequently, the indicated chemical elements must be written in decreasing order of their ordinal numbers: I, Br, Cl, F.

Chemistry class 9 tickets with answers

Ticket number 1

DI Mendeleev's periodic law and periodic system of chemical elements. Regularities of changes in the properties of elements of small periods and main subgroups depending on their ordinal (atomic) number.

The periodic table has become one of the most important sources of information about the chemical elements they form. simple substancesah and connections.

Dmitry Ivanovich Mendeleev created the Periodic Table while working on his textbook "Fundamentals of Chemistry", achieving maximum consistency in the presentation of the material. The regularity of the change in the properties of the elements that form the system is called Of the Periodic Law.

According to the periodic law formulated by Mendeleev in 1869, the properties of chemical elements are periodically dependent on their atomic masses. That is, with an increase in the relative atomic mass, element properties are periodically repeated. *

Compare: the frequency with which the seasons change over time.

This regularity is sometimes violated, for example, argon (inert gas) exceeds the weight of the next potassium (alkali metal). This contradiction was explained in 1914 when studying the structure of the atom. The ordinal number of an element in the Periodic Table is not just a sequence, it has a physical meaning - it is equal to the charge of the atomic nucleus. therefore

the modern formulation of the Periodic Law sounds like this:

The properties of chemical elements, as well as the substances formed by them, are periodically dependent on the charge of the atomic nucleus.

A period is a sequence of elements arranged in ascending order of the atomic nucleus charge, starting with an alkali metal and ending with an inert gas.

In the period, with an increase in the charge of the nucleus, the electronegativity of the element increases, the metallic (reducing) properties weaken and the non-metallic (oxidizing) properties of simple substances grow. So, the second period begins with an alkali metal lithium, followed by beryllium, which exhibits amphoteric properties, boron is a non-metal, etc. At the end, fluorine is a halogen and neon is an inert gas.

(The third period begins again with an alkali metal - this is the periodicity)

1-3 periods are small (contain one row: 2 or 8 elements), 4-7 are large periods, consist of 18 or more elements.

Composing the periodic system, Mendeleev combined the elements known at that time that have similarities into vertical columns. Groups are vertical columns of elements that, as a rule, have a valency in the higher oxide equal to the group number. The group is divided into two subgroups:

The main subgroups contain elements of small and large periods, form families with similar properties (alkali metals - I A, halogens - VII A, inert gases - VIII A).

(chemical signs elements of the main subgroups in the periodic system are located under the letter "A" or, in very old tables, where there are no letters A and B - under the element of the second period)

Side subgroups contain elements of only large periods, they are called transition metals.

(under the letter "B" or "B")

In the main subgroups, with an increase in the nuclear charge ( atomic number) metallic (reducing) properties grow.

* more precisely, substances formed by elements, but this is often omitted, saying "properties of elements"

In this lesson, you will learn about the patterns of change in the electronegativity of elements in a group and period. On it you will consider what determines the electronegativity of chemical elements. Using the elements of the second period as an example, study the patterns of change in the electronegativity of an element.

Topic: Chemical bond. Electrolytic dissociation

Lesson: Regularities of changes in the electronegativity of chemical elements in the group and period

1. Regularities of changes in the values \u200b\u200bof electronegativity in the period

Regularities of changes in the values \u200b\u200bof relative electronegativity in the period

Consider the example of the elements of the second period, the patterns of changes in the values \u200b\u200bof their relative electronegativity. Fig. 1.

Figure: 1. Regularities of changes in the values \u200b\u200bof electronegativity of period 2 elements

The relative electronegativity of a chemical element depends on the charge of the nucleus and on the radius of the atom. In the second period there are elements: Li, Be, B, C, N, O, F, Ne. From lithium to fluorine, the nuclear charge and the number of external electrons increase. The number of electronic layers remains unchanged. This means that the force of attraction of external electrons to the nucleus will increase, and the atom will, as it were, contract. The radius of the atom from lithium to fluorine will decrease. The smaller the radius of the atom, the stronger the external electrons are attracted to the nucleus, which means the greater the value of the relative electronegativity.

In the period with an increase in the nuclear charge, the radius of the atom decreases, and the value of the relative electronegativity increases.

Figure: 2. Regularities of changes in the values \u200b\u200bof electronegativity of elements of the VII-A group.

2. Regularities of changes in the values \u200b\u200bof electronegativity in the group

Regularities of changes in the values \u200b\u200bof relative electronegativity in the main subgroups

Let us consider the patterns of changes in the values \u200b\u200bof relative electronegativity in the main subgroups using the example of elements of the VII-A group. Fig. 2. In the seventh group, the main subgroup contains halogens: F, Cl, Br, I, At. On the outer electron layer, these elements have the same number of electrons - 7. With an increase in the charge of the atomic nucleus during the transition from period to period, the number of electronic layers increases, which means that the atomic radius increases. The smaller the radius of the atom, the greater the value of electronegativity.

In the main subgroup, with an increase in the charge of the atomic nucleus, the radius of the atom increases, and the value of relative electronegativity decreases.

Since the chemical element fluorine is located in the upper right corner of the Periodic Table of D. I. Mendeleev, its value of relative electronegativity will be maximum and numerically equal to 4.

Conclusion:The relative electronegativity increases with decreasing atomic radius.

In periods with an increase in the charge of the atomic nucleus, electronegativity increases.

In the main subgroups, with an increase in the charge of the atomic nucleus, the relative electronegativity of a chemical element decreases. The most electronegative chemical element is fluorine, as it is located in the upper right corner of D. I. Mendeleev's Periodic Table.

Lesson summary

In this lesson, you learned about the patterns of change in the electronegativity of elements in a group and period. On it, you examined what the electronegativity of chemical elements depends on. Using the elements of the second period as an example, we studied the regularities of changes in the electronegativity of an element.

1. Rudzitis G. E. Inorganic and organic chemistry... Grade 8: textbook for educational institutions: basic level / G. E. Rudzitis, F. G. Feldman. M .: Education. 2011 176s.: Ill.

2. Popel P. P. Chemistry: grade 8: textbook for general education institutions / P. P. Popel, L. S. Krivlya. - К .: IC "Academy", 2008.-240 p .: ill.

3. Gabrielyan OS Chemistry. Grade 9. Textbook. Publisher: Bustard.: 2001. 224s.

1. Chemport. ru.

1. Nos. 1,2,5 (p. 145) Rudzitis G. Ye. Inorganic and organic chemistry. Grade 8: textbook for educational institutions: basic level / G. E. Rudzitis, F. G. Feldman. M .: Education. 2011 176s.: Ill.

2. Give examples of substances with covalent non-polar connection and ionic. What is the significance of electronegativity in the formation of such compounds?

3. Arrange in ascending order of electronegativity the elements of the second group of the main subgroup.

Page 3

In the main subgroups of groups I-II periodic system located s - elements related in a free state to typical metals.

The atoms of the elements of the main subgroup of group V of the periodic system have 5 electrons in the outer electron shells. However, if the assumption of the highest positive valence equal to 5 is fully justified for nitrogen analogs - phosphorus, arsenic - antimony and bismuth, then for nitrogen itself it can be accepted only conditionally.

The atoms of the elements of the main subgroup of group VIII of the periodic system have increased chemical strength because their outer electron shells, which have 2 or 8 electrons, are characterized by high stability.

Of the elements of the main subgroup IV of group of the periodic table, carbon and silicon are not metals, and germanium, tin and lead are typical metals.

The atoms of all the elements of the main subgroup of group VII of the periodic system, called halogens, have seven electrons in the outer layer. According to the structure of the outer electron shell, all halogens tend to attach one more electron, which provides a stable configuration of the outer shell of eight electrons, the so-called electronic octet. Therefore, all halogens are most characterized by a negative valence equal to one. It should be remembered that the concepts of negative and positive valence are inherent in the theory of ionic bonds, while most of the actually existing compounds are compounds with a covalent bond. Therefore, without a big mistake, the valence of halogens can be considered equal to - 1 in compounds such as NaCl or CaF2, however, in compounds BF3 or CC14, the negative valence of halogens - 1 can only be said conditionally. Indeed, the electron pairs of covalent connections B-F and С - С1 are displaced towards halogen atoms, but are not completely torn off from boron and carbon atoms, therefore the value of the negative charge on each halogen atom is less than the charge of one electron and is only a fraction of it. Nevertheless, here and in what follows we will use the concepts of negative and positive valence, recognizing their greater or lesser convention for different compounds.

The main minerals of the elements of the main subgroup of group II of the periodic system are listed in table. 1.3. Beryl - beryllium aluminosilicate ZBeO-A12Oz-65Yu2 (or, what is the same, Be3 [Al2Si6Oi8]) has a color that depends on small impurities. Monocrystalline samples of beryl containing chromium are known as gemstones - emeralds; aquamarine is a modification of beryl containing an admixture of Fe (III), aquamarine. The main amount of the mineral, beryl, which is processed by industry, is not colored, and monocrystalline samples of colorless beryl are not a mineralogical rarity. In addition to aluminosilicates, minerals based on Fe silicate or aluminate are found. A large amount of magnesium in the form of sulfate and bicarbonate is present in natural waters.

The study of the properties of the elements of the main subgroup of group V of the periodic table of D. I. Mendeleev and their compounds shows that some of them exhibit non-metallic properties, others - metallic. Nitrogen is a typical non-metal, it forms a simple substance, consisting of N2 molecules and which is a gas.

Almost all the elements of the main subgroups IV-VII of groups of the periodic system are non-metals, while the elements side subgroups - metals. Therefore, on the right side of the periodic table, differences in the properties of elements of the main and secondary subgroups are especially pronounced. However, in cases where the elements of the main and secondary subgroups are in the highest oxidation state, their analogous compounds show significant similarity. In the same way, the oxides of manganese and chlorine, corresponding to the highest oxidation state of these elements, Mn2O7 and CbOr, have similar properties and are anhydrides of strong acids corresponding to general formula NEO.

Almost all the elements of the main subgroups IV-VII of groups of the periodic system are non-metals, while the elements of the secondary subgroups are metals. Therefore, on the right side of the periodic table, the differences in the properties of the elements of the main and secondary subgroups are especially pronounced. However, in cases where the elements of the main and secondary subgroups are in the highest oxidation state, their analogous compounds show significant similarity.

Almost all the elements of the main subgroups IV-VII of groups of the periodic system are non-metals, while the elements of the secondary subgroups are metals.

Photometric reactions of the elements of the main subgroup of group V of the Periodic Table of the Elements, suitable for differential spectrophotometry.

Boron belongs to the main subgroup III of group of the periodic system of elements and has the electronic configuration Is22s22p; underneath is aluminum. In the second period, when passing from boron to carbon, the atomic radii decrease, and in group IV, when passing from carbon to silicon, they increase. Therefore, the radii of boron and silicon atoms are close. Boron differs significantly from aluminum and shows a greater similarity to silicon. Boron forms three covalent bonds with atoms of other elements. Depending on the nature of the latter, the boron atom can form another donorxn acceptor bond, providing a p-orbital for electronic pair another atom.

Boron is included in the main subgroup of group III of the periodic system of elements and has an electronic configuration ls22s22 / 7; underneath is aluminum. In the second period, when passing from boron to carbon, the atomic radii decrease, and in group IV, when passing from carbon to silicon, they increase. Therefore, the radii of boron and silicon atoms are close. Boron differs significantly from aluminum and shows great similarity to silicon. Boron forms three covalent bonds with atoms of other elements. Depending on the nature of the latter, the boron atom can form another donor-acceptor bond, providing a p-orbital for the electron pair of another atom. Thus, boron in compounds exhibits a valency of three, or a covalence of four.