How do acidic properties of hydrogen compounds change. Acid-base properties of hydrogen and hydroxide compounds

With oxygen, non-metals form acidic oxides. In some oxides, they exhibit a maximum oxidation state equal to the group number (for example, SO2, N2O5), while in others, a lower one (for example, SO2, N2O3). Acid oxides correspond to acids, and of the two oxygen acids of one non-metal, the one in which it exhibits a higher degree of oxidation is stronger. For example, nitric acid HNO3 is stronger than nitrous HNO2, and sulfuric acid H2SO4 is stronger than sulphurous H2SO3.

Characteristics of oxygen compounds of non-metals:

The properties of higher oxides (that is, oxides that include an element of this group with the highest oxidation state) in periods from left to right gradually change from basic to acidic.

In groups from top to bottom, the acidic properties of higher oxides gradually weaken. This can be judged by the properties of the acids corresponding to these oxides.

The increase in the acidic properties of higher oxides of the corresponding elements in periods from left to right is explained by a gradual increase in the positive charge of the ions of these elements.

In the main subgroups of the periodic system of chemical elements in the direction from top to bottom, the acidic properties of higher oxides of non-metals decrease.

The general formulas of hydrogen compounds according to the groups of the periodic system of chemical elements are given in table No. 3.

Table #3

With metals, hydrogen forms (with a few exceptions) non-volatile compounds, which are non-molecular solids. Therefore, their melting points are relatively high.

With non-metals, hydrogen forms volatile compounds of a molecular structure. Under normal conditions, these are gases or volatile liquids.

In periods from left to right, the acidic properties of volatile hydrogen compounds of non-metals in aqueous solutions are enhanced. This is due to the fact that oxygen ions have free electron pairs, and hydrogen ions have a free orbital, then a process takes place that looks like this:

H2O + HF H3O + F

Hydrogen fluoride in an aqueous solution splits off positive hydrogen ions, i.e. exhibits acidic properties. Another circumstance also contributes to this process: the oxygen ion has an unshared electron pair, and the hydrogen ion has a free orbital, due to which a donor-acceptor bond is formed.

When ammonia is dissolved in water, the opposite process occurs. And since nitrogen ions have an unshared electron pair, and hydrogen ions have a free orbital, an additional bond arises and ammonium ions NH4 + and hydroxide ions OH- are formed. As a result, the solution acquires basic properties. This process can be expressed by the formula:

H2O + NH3 NH4 + OH

Ammonia molecules in an aqueous solution add positive hydrogen ions, i.e. ammonia exhibits basic properties.

Now consider why the hydrogen compound of fluorine - hydrogen fluoride HF - in an aqueous solution is an acid, but weaker than hydrochloric acid. This is due to the fact that the radii of fluorine ions are much smaller than those of chlorine ions. Therefore, fluorine ions attract hydrogen ions much more strongly than chloride ions. In this regard, the degree of dissociation of hydrofluoric acid is much less than that of hydrochloric acid, i.e. hydrofluoric acid is weaker than hydrochloric acid.

From these examples, the following general conclusions can be drawn:

In periods from left to right, the positive charge of the ions of the elements increases. In this regard, the acidic properties of volatile hydrogen compounds of elements in aqueous solutions are enhanced.

In groups, from top to bottom, negatively charged anions attract more and more weakly positively charged hydrogen ions H+. In this regard, the process of splitting off hydrogen ions H + is facilitated and the acidic properties of hydrogen compounds increase.

Hydrogen compounds of non-metals, which have acidic properties in aqueous solutions, react with alkalis. Hydrogen compounds of non-metals, which have basic properties in aqueous solutions, react with acids.

The oxidizing activity of hydrogen compounds of non-metals in groups from top to bottom increases greatly. For example, it is impossible to oxidize fluorine from the hydrogen compound HF chemically, but chlorine can be oxidized from the hydrogen compound HCl by various oxidizing agents. This is explained by the fact that atomic radii sharply increase from top to bottom in groups, and therefore the return of electrons is facilitated.

Acid properties are those that are most pronounced in a given environment. There are a number of them. It is necessary to be able to determine the acidic properties of alcohols and other compounds, not only to reveal the content of the corresponding medium in them. It is also important for the recognition of the studied substance.

There are many tests for the presence of acidic properties. The most elementary - immersion in the indicator substance - litmus paper, which reacts to the content of hydrogen, turning pink or blushing. Moreover, a more saturated color demonstrates a stronger acid. And vice versa.

The acidic properties increase along with the increase in the radii of the negative ions and hence the atom. This provides easier detachment of hydrogen particles. This quality is a characteristic feature of strong acids.

There are the most characteristic acid properties. These include:

Dissociation (cleavage of the hydrogen cation);

Decomposition (formation and water under the influence of temperature and oxygen);

Interaction with hydroxides (as a result of which water and salt are formed);

Interaction with oxides (as a result, salt and water are also formed);

Interaction with metals preceding hydrogen in the activity series (salt and water are formed, sometimes with gas evolution);

Interaction with salts (only if the acid is stronger than the one that formed the salt).

Often chemists have to make acids themselves. There are two ways to get them out. One of them is mixing acidic oxide with water. This method is used most often. And the second is the interaction of a strong acid with a weaker salt. It is used less frequently.

It is known that acidic properties are manifested and in many they can be more or less pronounced, depending on K, the properties of alcohols are manifested in the ability to split off a hydrogen cation when interacting with alkalis and metals.

Alcoholates - salts of alcohols - are able to hydrolyze under the action of water and release alcohol with metal hydroxide. This proves that the acidic properties of these substances are weaker than those of water. Consequently, the environment is expressed in them more strongly.

The acidic properties of phenol are much stronger due to the increased polarity of the OH compound. Therefore, this substance can also react with alkaline earth and alkali metal hydroxides. As a result, salts - phenolates are formed. To identify phenol, it is most effective to use with (III), in which the substance acquires a blue-violet color.

So, the acidic properties in various compounds manifest themselves in the same way, but with different intensity, which depends on the structure of the nuclei and the polarity of the hydrogen bonds. They help determine the environment of a substance and its composition. Along with these properties, there are also basic ones, which increase with the weakening of the first.

All these characteristics appear in most complex substances and form an important part of the world around us. After all, it is at their expense that many processes take place not only in nature, but also in living organisms. Therefore, acidic properties are extremely important, without them life on earth would be impossible.

Modern wording Periodic Law : the properties of simple substances, as well as the forms and properties of compounds of elements, are in a periodic dependence on the magnitude of the charge of the nuclei of their atoms (serial number).

Periodic properties are, for example, the radius of an atom, ionization energy, electron affinity, electronegativity of an atom, as well as some physical properties of elements and compounds (melting and boiling points, electrical conductivity, etc.).

The expression of the Periodic Law is

periodic table of elements .

The most common version of the short form of the periodic system, in which the elements are divided into 7 periods and 8 groups.

At present, the nuclei of atoms of elements up to number 118 have been obtained. The name of the element with the serial number 104 is rutherfordium (Rf), 105 is dubnium (Db), 106 is seaborgium (Sg), 107 is bohrium (Bh), 108 is hassium (Hs ), 109 – meitnerium ( Mt), 110 - darmstadtium (Ds), 111 - roentgenium (Rg), 112 - copernicium (Cn).
On October 24, 2012, in Moscow, at the Central House of Scientists of the Russian Academy of Sciences, a solemn ceremony was held to name the 114th element "Flerovium" (Fl), and the 116th - "Livermorium" (Lv).

Periods 1, 2, 3, 4, 5, 6 contain 2, 8, 8, 18, 18, 32 elements, respectively. The seventh period is not completed. Periods 1, 2 and 3 are called small the rest - large.

In periods from left to right, metallic properties gradually weaken and non-metallic properties increase, since with an increase in the positive charge of the nuclei of atoms, the number of electrons in the outer electron layer increases and a decrease in the atomic radii is observed.

At the bottom of the table are placed 14 lanthanides and 14 actinides. Recently, lanthanum and actinium have been classified as lanthanides and actinides, respectively.

Groups are divided into subgroups - main, or subgroups A and side, or subgroup B. Subgroup VIII B - special, it contains triads elements that make up the families of iron (Fe, Co, Ni) and platinum metals (Ru, Rh, Pd, Os, Ir, Pt).

From top to bottom, in the main subgroups, metallic properties increase and non-metallic properties weaken.

The group number, as a rule, indicates the number of electrons that can participate in the formation of chemical bonds. This is the physical meaning of the group number. For elements of secondary subgroups, the valence electrons are not only the outer, but also the penultimate layers. This is the main difference in the properties of the elements of the main and secondary subgroups.

Periodic system and electronic formulas of atoms

To predict and explain the properties of elements, it is necessary to be able to write down the electronic formula of an atom.

In an atom located in basic condition, each electron occupies a vacant orbital with the lowest energy. The energy state is determined primarily by temperature. The temperature on the surface of our planet is such that the atoms are in the ground state. At high temperatures, other states of atoms, which are called excited.

The sequence of energy levels in ascending order of energy is known from the results of solving the Schrödinger equation:

1s< 2s < 2p < 3s < Зр < 4s 3d < 4p < 5s 4d < 5p < 6s 5d 4f < 6p.

Consider the electronic configurations of atoms of some elements of the fourth period (Fig. 6.1).



Rice. 6.1. The distribution of electrons over the orbitals of some elements of the fourth period

It should be noted that there are some features in the electronic structure of the atoms of elements of the fourth period: for atoms Cr and С u by 4 s-shell contains not two electrons, but one, i.e., there is "failure" external s -electron to the previous d-shell.

Electronic formulas of 24 Cr and 29 Cu atoms can be represented as follows:

24 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 ,

29 Cu 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1 .

The physical reason for the “violation” of the filling order is related to the different penetrating power of electrons into the inner layers, as well as the special stability of the electronic configurations d 5 and d 10 , f 7 and f 14 .

All elements are divided into four types

:

1. At atoms s-elements filled with s - outer layer shells ns . These are the first two elements of each period.

2. At atoms p-elements electrons fill the p-shells of the outer level np . These include the last 6 elements of each period (except the first and seventh).

3. Do d-elements filled with electrons d - sublevel of the second outside level ( n-1)d . These are elements of intercalated decades of large periods located between s- and p-elements.

4. Do f-elements filled with electrons f - sublevel of the third outside level ( n-2)f . These are the lanthanides and actinides.

Changes in the acid-base properties of compounds of elements by groups and periods of the periodic system
(Kossel scheme)

To explain the nature of the change in the acid-base properties of the compounds of the elements, Kossel (Germany, 1923) proposed using a simple scheme based on the assumption that there is a purely ionic bond in the molecules and that the Coulomb interaction takes place between the ions. The Kossel scheme describes the acid-base properties of compounds containing E–H and E–O–H bonds, depending on the charge of the nucleus and the radius of the element forming them.

Kossel scheme for two metal hydroxides (for LiOH and KOH molecules ) is shown in Fig. 6.2. As can be seen from the presented scheme, the ion radius Li + less than the ion radius K+ and OH - group is more strongly bonded to the lithium ion than to the potassium ion. As a result, KOH will be easier to dissociate in solution and the basic properties of potassium hydroxide will be more pronounced.



Rice. 6.2. Kossel scheme for LiOH and KOH molecules

Similarly, one can analyze the Kossel scheme for two bases CuOH and Cu(OH) 2 . Since the radius of the Cu ion 2+ less, and the charge is greater than that of an ion Cu + OH - - the group will be stronger to hold the Cu 2+ ion .
As a result, the base Cu(OH)2 will be weaker than CuOH.

Thus, base strength increases as the cation radius increases and its positive charge decreases .

Kossel's scheme for the two anoxic acids HCl and HI shown in fig. 6.3.



Rice. 6.3. Kossel scheme for HCl and HI molecules

Since the radius of the chloride ion is smaller than that of the iodide ion, the H + ion more strongly bound to the anion in the hydrochloric acid molecule, which will be weaker than hydroiodic acid. Thus, the strength of anoxic acids increases with increasing negative ion radius.

The strength of oxygen-containing acids changes in the opposite way. It increases with a decrease in the ion radius and with an increase in its positive charge. On fig. 6.4 shows the Kossel scheme for two acids HClO and HClO 4 .



Rice. 6.4. Kossel scheme for HClO and HClO 4

Ion С1 7+ is strongly bound to the oxygen ion, so the proton will be more easily split off in the HClO molecule 4 . At the same time, the bond of the C1 ion+ with O ion 2- less strong, and in the HClO molecule the proton will be more strongly retained by the O anion 2-. As a result, HClO 4 is a stronger acid than HClO.

Thus, an increase in the oxidation state of an element and a decrease in the radius of the element's ion enhance the acidic nature of the substance. On the contrary, a decrease in the degree of oxidation and an increase in the radius of the ion enhance the basic properties of substances.

Examples of problem solving

Compose electronic formulas of the zirconium atom and ions O 2–, Al 3+, Zn 2+ . Determine what type of elements Zr, O, Zn, Al atoms belong to.

40 Zr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 2 5s 2 ,

O 2– 1s 2 2s 2 2p 6 ,

Zn 2+ 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 ,

Al 3+ 1s 2 2s 2 2p 6 ,

Zr - d-element, O - p-element, Zn - d-element, Al - p-element.

Arrange the atoms of the elements in order of increasing ionization energy: K, Mg, Be, Ca. Justify the answer.

Decision. Ionization energy is the energy required to detach an electron from an atom in the ground state. In the period from left to right, the ionization energy increases with increasing nuclear charge, in the main subgroups from top to bottom it decreases, as the distance from the electron to the nucleus increases.

Thus, the value of the ionization energy of the atoms of these elements increases in the series K, Ca, Mg, Be.

Arrange atoms and ions in ascending order of their radii: Ca 2+ , Ar, Cl – , K + , S 2– . Justify the answer.

Decision. For ions containing the same number of electrons (isoelectronic ions), the radius of the ion will increase with a decrease in positive and an increase in its negative charge. Therefore, the radius increases in the series Ca 2+ , K + , Ar, Cl – , S 2– .

Determine how the radii of ions and atoms change in the series Li + , Na + , K + , Rb + , Cs + and Na, Mg, Al, Si, P, S.

Decision. In the series Li + , Na + , K + , Rb + , Cs + the radius of the ions increases, since the number of electron layers increases in ions of the same sign with a similar electronic structure.

In the series Na, Mg, Al, Si, P, S, the radius of atoms decreases, since with the same number of electron layers in atoms, the charge of the nucleus increases, and, hence, the attraction of electrons by the nucleus.

Compare the strength of the acids H 2 SO 3 and H 2 SeO 3 and the bases Fe (OH) 2 and Fe (OH) 3.

Decision. According to the Kossel scheme H 2 SO 3 stronger acid than H 2 SeO 3 , since the ion radius Se4+ greater than the ion radius S 4+, therefore, the bond S 4+ - O 2– is stronger than bond Se 4+ - O 2-.

According to the Kossel scheme, Fe(OH)

2 stronger base, because the radius of the Fe ion 2+ more than Fe ion 3+ . In addition, the charge of the Fe ion 3+ more than the Fe ion 2+ . As a result, the bond Fe 3+ – O 2– is stronger than Fe 2+ - O 2- and OH ion - easily split off in the molecule Fe(OH)2.

Tasks for independent solution

6.1.Compose electronic formulas of elements with a nuclear charge of +19, +47, +33 and in the ground state. Specify what type of elements they belong to. What oxidation states are typical for an element with a nuclear charge of +33?




6.2.Compose the electronic formula of the ion Cl – .

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AKHMETOV M. A. LESSON 3. ANSWERS TO TASKS.

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Periodic law and the periodic system of chemical elements. Radii of atoms, their periodic changes in the system of chemical elements. Patterns of changes in the chemical properties of elements and their compounds by periods and groups.

1. Arrange the following chemical elements N, Al, Si, C in order of increasing their atomic radii.

ANSWER:

NandClocated in the same period. To the right is locatedN. So nitrogen is less than carbon.

C andSilocated in the same group. But C is higher. So C is less thanSi.

SiandAllocated in one third period, but to the right isSi, meansSiless thanAl

The order of increasing the size of atoms will be as follows:N, C, Si, Al

2. Which of the chemical elements phosphorus or oxygen exhibits more pronounced non-metallic properties? Why?

ANSWER:

Oxygen exhibits more pronounced non-metallic properties, since it is located above and to the right in the periodic system of elements.

3. How do the properties of group IV hydroxides of the main subgroup change when moving from top to bottom?

ANSWER:

The properties of hydroxides change from acidic to basic. SoH2 CO3 - carbonic acid, as its name implies, exhibits acidic properties, andPb(Oh)2 is the base.

ANSWERS TO TESTS

A1. The strength of oxygen-free acids of non-metals of group VIIA, according to the increase in the charge of the nucleus of atoms of elements

	increases
	decreases
	does not change
	changes periodically

ANSWER: 1

It's about acids.HF, HCl, HBr, HI. In a rowF, Cl, Br, Ian increase in the size of the atoms. Therefore, the internuclear distance increasesH– F, H– Cl, H– Br, H– I. And if so, it means that the bond energy is weakening. And the proton is more easily split off in aqueous solutions

A2. The element has the same valence value in the hydrogen compound and the higher oxide

	germanium

ANSWER: 2

Of course, we are talking about an element of the 4th group (see period. c-th elements)

A3. In which order are simple substances arranged in order of increasing metallic properties?

ANSWER: 1

The metallic properties in a group of elements are known to increase from top to bottom.

A4. In the series Na ® Mg ® Al ®Si

	the number of energy levels in atoms increases
	the metallic properties of the elements are enhanced
	the highest oxidation state of elements decreases
	weaken the metallic properties of the elements

ANSWER: 4

In the period from left to right, non-metallic properties are enhanced, and metallic properties are weakened.

A5. For elements of the carbon subgroup, with increasing atomic number, the

ANSWER: 4.

Electronegativity is the ability to move electrons towards itself when a chemical bond is formed. Electronegativity is almost directly related to non-metallic properties. The non-metallic properties decrease, and the electronegativity also decreases.

A6. In the series of elements: nitrogen - oxygen - fluorine

increases

ANSWER: 3

The number of outer electrons is equal to the group number

A7. Among the chemical elements:

boron - carbon - nitrogen

increases

ANSWER:2

The number of electrons in the outer layer is equal to the highest oxidation state except for (F, O)

A8. Which element has more pronounced non-metallic properties than silicon?

ANSWER: 1

Carbon is in the same group as silicon, only higher.

A9. The chemical elements are arranged in ascending order of their atomic radius in the following order:

ANSWER: 2

In groups of chemical elements, the atomic radius increases from top to bottom.

A10. The metallic properties of the atom are most pronounced:

1) lithium 2) sodium

3) potassium 4) calcium

ANSWER: 3

Among these elements, potassium is located below and to the left.

A11. The most pronounced acidic properties:

Answer: 4 (see answer to A1)

A12. Acid properties of oxides in the series SiO2 ® P2O5 ®SO3

1) weaken

2) intensify

3) do not change

4) change periodically

ANSWER: 2

The acid properties of oxides, as well as non-metallic properties, increase in periods from left to right

A13. With an increase in the charge of the nucleus of atoms, the acidic properties of oxides in the series

N2O5 ® P2O5 ®As2O5 ® Sb2O5

1) weaken

2) intensify

3) do not change

4) change periodically

ANSWER: 1

In groups from top to bottom, acidic properties, like non-metallic ones, weaken

A14. Acidic Properties of Hydrogen Compounds of Group VIA Elements with Increasing Ordinal Number

1) amplify

2) weaken

3) remain unchanged

4) change periodically

ANSWER: 3

The acidic properties of hydrogen compounds are related to the binding energyH- El. This energy from top to bottom weakens, which means that the acidic properties are enhanced.

A15. The ability to donate electrons in the series Na ® K ® Rb ®Cs

1) is weakening

2) amplifies

3) does not change

4) changes periodically

ANSWER: 2

In this series, the number of electron layers and the distance of electrons from the nucleus increase, therefore, the ability to donate an external electron increases.

A16. In the series Al ®Si ®P ®S

1) the number of electron layers in atoms increases

2) non-metallic properties are enhanced

3) the number of protons in the nuclei of atoms decreases

4) the radii of atoms increase

ANSWER: 2

In the period with an increase in the charge of the nucleus, non-metallic properties are enhanced

A17. In the main subgroups of the periodic system, the reducing ability of atoms of chemical elements increases c

ANSWER: 1

With an increase in the number of electronic levels, the remoteness and screening of the outer electrons from the nucleus increases. Consequently, the ability to return them increases (restorative properties)

A18. According to modern ideas, the properties of chemical elements are periodically dependent on

ANSWER: 3

A19. Atoms of chemical elements that have the same number of valence electrons are located

	diagonally
	in one group
	in one subgroup
	in one period

ANSWER: 2

A20. The element with serial number 114 must have properties similar to

ANSWER: 3. This element will be located in the cell corresponding to the one occupied by lead inVIgroup

A21. In periods, the reducing properties of chemical elements from right to left

	increase
	decrease
	do not change
	change periodically

ANSWER: 1

The nuclear charge decreases.

A22. Electronegativity and ionization energy in the О–S–Se–Te series, respectively

	increases, increases
	increases, decreases
	decreases, decreases
	decreasing, increasing

ANSWER: 3

The electronegativity decreases as the number of filled electron layers increases. Ionization energy is the energy required to remove an electron from an atom. She also shrinks

A23. In which order are the signs of chemical elements arranged in order of increasing atomic radii?

3. Periodic law and the periodic system of chemical elements

3.4. Periodic change in the properties of substances

The following properties of simple and complex substances change periodically:

• the structure of simple substances (initially non-molecular, for example from Li to C, and then molecular: N 2 - Ne);
• the melting and boiling points of simple substances: when moving from left to right along the period t melt and t boil, at first, in general, they increase (diamond is the most refractory substance), and then decrease, which is associated with a change in the structure of simple substances (see above);
• metallic and non-metallic properties of simple substances. Over the period, with increasing Z, the ability of atoms to donate an electron decreases (E and increases), respectively, the metallic properties of simple substances weaken (non-metallic ones increase, since E cf atoms increases). From top to bottom in groups A, on the contrary, the metallic properties of simple substances are enhanced, while non-metallic ones are weakened;
• composition and acid-base properties of oxides and hydroxides (Tables 3.1–3.2).

Table 3.1

The composition of higher oxides and the simplest hydrogen compounds of elements of A-groups

As can be seen from Table. 3.1, the composition of higher oxides changes smoothly in accordance with the gradual increase in the covalence (oxidation state) of the atom.

With an increase in the charge of the nucleus of an atom in a period, the basic properties of oxides and hydroxides weaken, and the acid properties increase. The transition from basic oxides and hydroxides to acid ones in each period occurs gradually, through amphoteric oxides and hydroxides. As an example, in Table. 3.2 shows the change in the properties of oxides and hydroxides of elements of the 3rd period.

Table 3.2

Oxides and hydroxides formed by elements of the 3rd period and their classification

In groups A, with an increase in the charge of the atomic nucleus, the basic properties of oxides and hydroxides increase. For example, for the IIA-group we have:

1. BeO, Be (OH) 2 - amphoteric (weak basic and acidic properties).

2. MgO, Mg(OH) 2 - weak, basic properties.

3. CaO, Ca (OH) 2 - pronounced basic properties (alkalis).

4. SrO, Sr(OH) 2 - pronounced basic properties (alkalis).

5. BaO, Ba (OH) 2 - pronounced basic properties (alkalis).

6. RaO, Ra (OH) 2 - pronounced basic properties (alkalis).

The same trends can be traced for elements of other groups (composition and acid-base properties of binary hydrogen compounds, see Table 3.1). In general, with an increase in the atomic number over the period, the basic properties of hydrogen compounds weaken, and the acidic properties of their solutions increase: sodium hydride dissolves in water with the formation of alkali:

NaH + H 2 O \u003d NaOH + H 2,

and aqueous solutions of H 2 S and HCl are acids, with hydrochloric acid being stronger.

1. In groups A, with an increase in the charge of the atomic nucleus, the strength of oxygen-free acids also increases.

2. In hydrogen compounds, the number of hydrogen atoms in a molecule (or formula unit) first increases from 1 to 4 (groups IA–IVA), and then decreases from 4 to 1 (groups IVA–VIIA).

3. Volatile (gaseous) at n.o. are only hydrogen compounds of elements of groups IVA–VIIA (except for H 2 O and HF)

The described trends in the change in the properties of atoms of chemical elements and their compounds are summarized in Table. 3.3

Table 3.3

Change in the properties of atoms of elements and their compounds with an increase in the charge of the atomic nucleus

Properties	Change trend
	in periods	in groups A
Atom radius	Decreases	growing
Ionization energy	Increasing	Decreases
electron affinity	Increasing	Decreases
Reducing (metallic) properties of atoms	Weaken	Are getting stronger
Oxidative (non-metallic) properties of atoms	Are getting stronger	Weaken
Electronegativity	Increasing	Decreases
Maximum oxidation state	Increasing	Constant
Acid properties of oxides	Are getting stronger	Weaken
Acid properties of hydroxides	Are getting stronger	Weaken
Acidic properties of hydrogen compounds	Are getting stronger	Are getting stronger
Metallic properties of simple substances	Weaken	Are getting stronger
Non-metallic properties of simple substances	Are getting stronger	Weaken

Example 3.3. Specify the formula of the oxide with the most pronounced acidic properties:

Decision. The acidic properties of oxides increase from left to right along the period, and weaken from top to bottom in group A. With this in mind, we come to the conclusion that the acidic properties are most pronounced in the oxide Cl 2 O 7 .

Answer: 4).

Example 3.4. The anion of the element E 2− has the electronic configuration of the argon atom. Specify the formula of the highest oxide of the element atom:

Decision. The electronic configuration of the argon atom is 1s 2 2s 2 2p 6 3s 2 3p 6, therefore the electronic configuration of the atom E (atom E contains 2 electrons less than the ion E 2−) - 1s 2 2s 2 2p 6 3s 2 3p 4, which corresponds to the atom sulfur. The element sulfur is in the VIA group, the formula of the highest oxide of the elements of this group is EO 3.

Answer: 1).

Example 3.5. Indicate the symbol of the element whose atom has three electron layers and forms a volatile (n.o.) compound of the composition EN 2 (H 2 E):

Decision. Hydrogen compounds of the composition EN 2 (H 2 E) form atoms of elements of the IIA- and VIA-groups, however, they are volatile at n.o. are compounds of elements of the VIA-group, which include sulfur.

Answer: 3).

The characterized trends in the change in the acid-base properties of oxides and hydroxides can be understood on the basis of the analysis of the following simplified schemes for the structure of oxides and hydroxides (Fig. 3.1).

From a simplified reaction scheme

it follows that the efficiency of the interaction of the oxide with water with the formation of a base increases (according to the Coulomb law) with an increase in the charge on the ion E n + . The magnitude of this charge increases as the metallic properties of the elements increase, i.e. from right to left across the period and from top to bottom across the group. It is in this order that the main properties of the elements increase.

Rice. 3.1. Scheme of the structure of oxides (a) and hydroxides (b)

Let us consider the reasons underlying the described changes in the acid-base properties of hydroxides.

With an increase in the degree of oxidation of the element + n and a decrease in the radius of the ion E n + (this is exactly what is observed with an increase in the charge of the nucleus of the element's atom from left to right along the period), the E–O bond is strengthened, and the O–H bond weakens; the process of dissociation of the hydroxide according to the acid type becomes more probable.

From top to bottom in the group, the radius E n + increases, and the value of n + does not change, as a result, the strength of the E–O bond decreases, its rupture becomes easier, and the process of hydroxide dissociation according to the main type becomes more likely.