Patterns of change in the electronegativity of elements in a group and period. Patterns of change in the electronegativity of elements in a group and period In which direction does the electronegativity increase

Electronegativity - the ability of atoms to shift electrons in their direction when a chemical bond is formed. This concept was introduced by the American chemist L. Pauling (1932). Electronegativity characterizes the ability of an atom of a given element to attract a common electron pair in a molecule. Electronegativity values ​​determined in different ways differ from each other. In educational practice, most often they use not absolute, but relative values ​​of electronegativity. The most common is the scale in which the electronegativity of all elements is compared with the electronegativity of lithium, taken as one.

Among the elements of groups IA - VIIA:

electronegativity with increasing serial number, as a rule, increases in periods (“from left to right”), and decreases in groups (“top to bottom”).

The patterns of change in electronegativity among the elements of the d-block are much more complex.

Elements with high electronegativity, whose atoms have a high affinity for an electron and a high ionization energy, i.e., prone to attaching an electron or shifting a pair of binding electrons in their direction, are called non-metals.

These include: hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, selenium, fluorine, chlorine, bromine, and iodine. According to a number of features, a standing group of noble gases (helium-radon) is also classified as a non-metal.

Most of the elements in the Periodic Table are metals.

Metals are characterized by low electronegativity, i.e., low values ​​of ionization energy and electron affinity. Metal atoms either donate electrons to non-metal atoms, or mix pairs of bonding electrons away from themselves. Metals are distinguished by their characteristic brilliance, high electrical conductivity and good thermal conductivity. They are mostly durable and malleable.

Such a set of physical properties that distinguish metals from non-metals is explained by a special type of bond that exists in metals. All metals have a well-defined crystal lattice. In its nodes, along with atoms, there are metal cations, i.e. atoms that have lost their electrons. These electrons form a socialized electron cloud, the so-called electron gas. These electrons are in the force field of many nuclei. Such a bond is called a metallic bond. The free migration of electrons over the volume of a crystal determines the special physical properties of metals.

Metals include all d and f elements. If we mentally select only blocks of s- and p-elements from the Periodic system, i.e. elements of group A and draw a diagonal from the upper left corner to the lower right corner, then it turns out that non-metallic elements are located on the right side of this diagonal, and metallic - in the left. Adjoining the diagonal are elements that cannot be attributed unequivocally to either metals or non-metals. These intermediate elements include: boron, silicon, germanium, arsenic, antimony, selenium, polonium, and astatine.

The concepts of covalent and ionic bonds played an important role in the development of ideas about the structure of matter, however, the creation of new physicochemical methods for studying the fine structure of matter and their use showed that the phenomenon of chemical bonding is much more complicated. It is currently believed that any heteroatomic bond is both covalent and ionic, but in different proportions. Thus, the concept of the covalent and ionic components of a heteroatomic bond is introduced. The greater the difference in the electronegativity of the bonding atoms, the greater the polarity of the bond. With a difference of more than two units, the ionic component is almost always predominant. Let's compare two oxides: sodium oxide Na 2 O and chlorine(VII) oxide Cl 2 O 7 . In sodium oxide, the partial charge on the oxygen atom is -0.81, and in chlorine oxide -0.02. This effectively means that the Na-O bond is 81% ionic and 19% covalent. The ionic component of the Cl-O bond is only 2%.

List of used literature

1. Popkov V. A., Puzakov S. A. General chemistry: textbook. - M.: GEOTAR-Media, 2010. - 976 p.: ISBN 978-5-9704-1570-2. [With. 35-37]
2. Volkov, A.I., Zharsky, I.M. Big chemical reference book / A.I. Volkov, I.M. Zharsky. - Minsk: Modern school, 2005. - 608 with ISBN 985-6751-04-7.

You can find out the activity of simple substances using the table of electronegativity of chemical elements. Denoted as χ. Read more about the concept of activity in our article.

What is electronegativity

The property of an atom of a chemical element to attract the electrons of other atoms to itself is called electronegativity. For the first time the concept was introduced by Linus Pauling in the first half of the twentieth century.

All active simple substances can be divided into two groups according to physical and chemical properties:

• metals;
• non-metals.

All metals are reducing agents. In reactions, they donate electrons and have a positive oxidation state. Non-metals can exhibit the properties of reducing and oxidizing agents depending on the value of electronegativity. The higher the electronegativity, the stronger the properties of the oxidizing agent.

Rice. 1. Actions of an oxidizing agent and a reducing agent in reactions.

Pauling created the electronegativity scale. In accordance with the Pauling scale, fluorine (4) has the highest electronegativity, and francium (0.7) has the lowest. This means that fluorine is the strongest oxidizing agent and is able to attract electrons from most elements. On the contrary, francium, like other metals, is a reducing agent. He seeks to give, not accept electrons.

Electronegativity is one of the main factors that determine the type and properties of a chemical bond formed between atoms.

How to determine

The properties of elements to attract or donate electrons can be determined from the electronegativity series of chemical elements. According to the scale, elements with a value of more than two are oxidizers and exhibit the properties of a typical non-metal.

Item number	Element	Symbol	Electronegativity
	Strontium
	Ytterbium
	Praseodymium
	Prometheus
	Americium
	Gadolinium
	Dysprosium
	Plutonium
	Californium
	Einsteinium
	Mendelevium
	Zirconium
	Neptunium
	Protactinium
	Manganese
	Beryllium
	Aluminum
	Technetium
	Molybdenum
	Palladium
	Tungsten
	Oxygen

Substances with an electronegativity of two or less are reducing agents and exhibit metallic properties. Transition metals, which have a variable degree of oxidation and belong to the side subgroups of the periodic table, have electronegativity values ​​in the range of 1.5-2. Elements with an electronegativity equal to or less than one have pronounced properties of a reducing agent. These are typical metals.

In the electronegativity series, metallic and reducing properties increase from right to left, while oxidizing and non-metallic properties increase from left to right.

Rice. 2. Series of electronegativity.

In addition to the Pauling scale, you can find out how pronounced the oxidizing or reducing properties of an element are using the periodic table of Mendeleev. Electronegativity increases in periods from left to right as the atomic number increases. In groups, the value of electronegativity decreases from top to bottom.

Rice. 3. Periodic table.

What have we learned?

Electronegativity refers to the ability of elements to donate or accept electrons. This characteristic helps to understand how pronounced the properties of an oxidizing agent (non-metal) or reducing agent (metal) are for a particular element. For convenience, Pauling developed the electronegativity scale. According to the scale, fluorine has the maximum oxidizing properties, and francium has the minimum. In the periodic table, the properties of metals increase from right to left and from top to bottom.

Topic quiz

Report Evaluation

Average rating: 4.6. Total ratings received: 75.

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 changes in the electronegativity of the element.

Topic: Chemical bond. Electrolytic dissociation

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

1. Patterns of changes in electronegativity values ​​in a period

Patterns of changes in the values ​​of relative electronegativity in the period

Consider, using the example of the elements of the second period, the patterns of changes in the values ​​of their relative electronegativity. Fig.1.

Rice. 1. Patterns of changes in the values ​​of the electronegativity of elements of the 2nd period

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 charge of the nucleus and the number of outer electrons increase. The number of electron 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, shrink. The radius of an atom from lithium to fluorine will decrease. The smaller the radius of the atom, the stronger the outer electrons are attracted to the nucleus, and hence the greater the value of the relative electronegativity.

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

Rice. 2. Patterns of changes in the values ​​of the electronegativity of elements of the VII-A group.

2. Patterns of changes in electronegativity values ​​in a group

Patterns of changes in the values ​​of relative electronegativity in the main subgroups

Let us consider the patterns of changes in the values ​​of relative electronegativity in the main subgroups using the elements of group VII-A as an example. 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 electron 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 the 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 as the radius of the atom decreases.

In periods with an increase in the charge of the nucleus of an atom, the 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, since it is located in the upper right corner of the Periodic Table of D. I. Mendeleev.

Summing up the lesson

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. On the example of elements of the second period, we studied the patterns of change in the electronegativity of the element.

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

2. Popel P. P. Chemistry: 8th grade: a textbook for general educational institutions / P. P. Popel, L. S. Krivlya. - K .: Information Center "Academy", 2008.-240 p.: ill.

3. Gabrielyan O. S. Chemistry. Grade 9 Textbook. Publisher: Drofa.: 2001. 224s.

1. Chemport. ru.

1. No. 1,2,5 (p. 145) Rudzitis G. E. Inorganic and organic chemistry. Grade 8: textbook for educational institutions: basic level / G. E. Rudzitis, F. G. Feldman. M.: Enlightenment. 2011 176 pp.: ill.

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

3. Arrange in a row in increasing electronegativity the elements of the second group of the main subgroup.

In complex compounds consisting of atoms of different elements, the electron density will always be shifted to one, the most “strong” neighbor. For example, in a water molecule (H 2 O), oxygen will be the winner, and in hydrochloric acid (HCl), the chlorine atom will win the duel. How to learn to determine this power? To do this, it is enough to disassemble what electronegativity is. Let's get started.

Atoms and elements

The first thing to be mastered is the difference between an atom and an element. Suppose there are as many as five atoms in the HNO 3 molecule and only three elements, which are hydrogen (H), nitrogen (N) and oxygen (O). If the name of some icon or symbol has been erased from memory, then Mendeleev's periodic system will come to the rescue.

It just lists all the elements that exist today. So, the first difficulty is overcome. Let's get closer to the question of what electronegativity is.

Pauling scale

In schools and universities, to identify the very strongest atom that will pull the electron density of weaker "neighbors" onto itself, the Pauling scale will be enough. You should not be afraid. Everything is extremely simple here. The relative electronegativity of chemical elements is arranged in ascending order and varies in the range of 0.7-4.0. The logic here is clear: whoever has this value is greater, he is stronger.

The value "0.7" belongs to the most active metal - France. Here he loses to absolutely everyone, that is, he is the least electronegative (the most electropositive). Fluorine boasts a maximum value of four. That is why he has no equal in strength.

Even without particularly understanding what electronegativity is, in any complex fluorine-containing compound, you can immediately determine the winner. Who will take over the electron density in lithium fluoride (LiF)? Of course, fluorine. Which element is more electronegative in silicon tetrafluoride (SiF 4)? Of course, again fluorine.

We consolidate the past

So, having analyzed what electronegativity is, let's support the theory with examples. Let's learn how to identify the strongest element present in the compound. Let's take a molecule of sulfuric acid (H 2 SO 4). Using the Pauling scale, we determine the relative electronegativity of all three required elements. For hydrogen, it will be 2.1. The value for sulfur is slightly higher - 2.6. But the clear leader will be oxygen, which has a maximum value of 3.5. This means that oxygen will be the most electronegative element in the H 2 SO 4 molecule. Thus, it is possible to determine the electronegativity value of any element.

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 changes in the electronegativity of the element.

Topic: Chemical bond. Electrolytic dissociation

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

Patterns of changes in the values ​​of relative electronegativity in the period

Consider, using the example of the elements of the second period, the patterns of changes in the values ​​of their relative electronegativity. Fig.1.

Rice. 1. Patterns of changes in the values ​​of the electronegativity of elements of the 2nd period

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 the elements are: Li, Be, B, C, N, O, F, Ne. From lithium to fluorine, the charge of the nucleus and the number of outer electrons increase. 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, shrink. The radius of an atom from lithium to fluorine will decrease. The smaller the radius of the atom, the stronger the outer electrons are attracted to the nucleus, and hence the greater the value of the relative electronegativity.

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

Rice. 2. Patterns of changes in the values ​​of the electronegativity of elements of the VII-A group.

Patterns of changes in the values ​​of relative electronegativity in the main subgroups

Let us consider the patterns of changes in the values ​​of relative electronegativity in the main subgroups using the elements of group VII-A as an example. 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 electron 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 the 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 as the radius of the atom decreases.

In periods with an increase in the charge of the nucleus of an atom, the 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, since it is located in the upper right corner of the Periodic Table of D.I. Mendeleev.

Summing up the lesson

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. On the example of elements of the second period, we studied the patterns of change in the electronegativity of the element.

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

2. Popel P.P. Chemistry: 8th class: a textbook for general educational institutions / P.P. Popel, L.S. Krivlya. -K.: IC "Academy", 2008.-240 p.: ill.

3. Gabrielyan O.S. Chemistry. Grade 9 Textbook. Publisher: Drofa.: 2001. 224s.

1. No. 1,2,5 (p. 145) Rudzitis G.E. Inorganic and organic chemistry. Grade 8: textbook for educational institutions: basic level / G. E. Rudzitis, F.G. Feldman. M.: Enlightenment. 2011 176 pp.: ill.

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

3. Arrange in a row in increasing electronegativity the elements of the second group of the main subgroup.