Oxygen and hydrogen compounds of nonmetals. Brief description of their properties

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

Characteristics of oxygen compounds of non-metals:

The properties of higher oxides (i.e. oxides that contain an element of a given group with the highest oxidation state) gradually change from basic to acidic in periods from left to right.

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 table chemical elements in the direction from top to bottom, the acidic properties of higher oxides of non-metals decrease.

General formulas of hydrogen compounds according to groups of the periodic system of chemical elements are given in Table No. 3.

Table No. 3

With metals, hydrogen forms (with some exceptions) non-volatile compounds, which are solid substances not molecular structure. Therefore, their melting points are relatively high.

With non-metals, hydrogen forms volatile compounds of 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 nonmetals in aqueous solutions increase. This is explained by the fact that oxygen ions have free electron pairs, and hydrogen ions have a free orbital, then a process occurs that looks like this:

H2O + HF H3O + F

Hydrogen fluoride in an aqueous solution removes positive hydrogen ions, i.e. exhibits acidic properties. This process is also facilitated by another circumstance: the oxygen ion has a lone 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 a lone 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 attach positive hydrogen ions, i.e. ammonia exhibits basic properties.

Now let's look at why the hydrogen compound of fluorine - hydrogen fluoride HF - in an aqueous solution is an acid, but weaker than hydrochloric acid. This is explained by 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 chlorine ions. In this regard, the degree of dissociation of hydrofluoric acid is significantly less than of hydrochloric acid, i.e. hydrofluoric acid is weaker than hydrochloric acid.

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

In periods from left to right, the positive charge of element ions 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 positively charged hydrogen ions H+ less and less. In this regard, the process of elimination of hydrogen ions H+ is facilitated and the acidic properties of hydrogen compounds increase.

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

The oxidative 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 using various oxidizing agents. This is explained by the fact that in groups from top to bottom the atomic radii increase sharply, and therefore the transfer of electrons becomes easier.

Acidic properties are those that are most pronounced in a given environment. There are a whole range of them. It is necessary to be able to determine the acidic properties of alcohols and other compounds not only to determine the content of the corresponding environment in them. This is also important for recognizing the substance being studied.

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

Acidic properties increase along with increasing radii of negative ions and, consequently, the atom. This ensures easier removal of hydrogen particles. This quality is a characteristic feature of strong acids.

There are the most characteristic acidic properties. These include:

Dissociation (elimination of a hydrogen cation);

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

Interaction with hydroxides (resulting in the formation of water and salt);

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 the release of gas);

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

Chemists often have to produce their own acids. There are two ways to remove them. One of them is mixing acid oxide with water. This method is used most often. And the second is the interaction of a strong acid with a salt of a weaker one. It is used somewhat less frequently.

It is known that acidic properties are manifested in many. They can be more or less expressed depending on K. The properties of alcohols are manifested in the ability to abstract a hydrogen cation when interacting with alkalis and metals.

Alcoholates - salts of alcohols - are capable of hydrolyzing under the influence of water and releasing alcohol with metal hydroxide. This proves that the acidic properties of these substances are weaker than those of water. Consequently, the environment is expressed more strongly in them.

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

So, acidic properties in different compounds manifest themselves in the same way, but with different intensities, which depends on the structure of the nuclei and the polarity of 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 through them 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.

General properties of main classes inorganic compounds. Conditions for the occurrence of “exchange reactions”.

1. Acid-base properties of hydrogen compounds.

A) Comment on the ability of water to self-ionize (equation, K W). Based on the structure of molecules (their polarizability), explain the patterns of changes in solubility in water and acid-base properties of the corresponding solutions of methane (CH 4), ammonia (NH 3), hydrogen fluoride (HF) and hydrogen chloride (HCl). Make up the necessary equations.

b) Using the concept of the polarizing effect of cations on the H–O bond, and also taking into account the number of hydroxo groups, explain the pattern of changes in the acid-base properties of hydroxides LiOH–Be(OH) 2 –H 3 BO 3 –H 2 CO 3 –HNO 3 –H 3 PO 4 –H 2 SO 4 –(H 2 SeO 4)–HClO 4. Create dissociation equations for the proposed substances.

2. Mandatory and optional(including special ones) reactions of acids and bases.

A) Which of the following substances (solutions) can 20% solutions of nitric, sulfuric and acetic acids react with: solutions of KOH, NH 3, H2S; Zn(OH)2, H3PO2; BaCl 2 and crystalline Cu, Ca 3 (PO 4) 2 .

b) Which of the following substances (solutions) can 20% solutions of potassium hydroxide and ammonia react with: solutions of H 2 SO 4, CH 3 COOH; Zn(OH)2, Al(OH) 3 ; MgCl 2 and crystalline Ag2O, AgCl.

In both versions of the experiment, the formulas of substances are highlighted in bold, the interaction with which will require writing non-obvious equations.

The task involves only a theoretical discussion, but... The reaction equations must be thought out and written in advance, including in ionic form.

3. Conditions for exchange reactions with salts.

Which exchange reactions can be performed using the proposed reagents: diluted solutions MnSO4, Ba(NO3)2, saturated solution SrSO 4, crystalline CuS And FeS, as well as concentrated solutions of HCl, CO 2 and NH 3. Consider the possibility of performing reactions that require the participation of salt. Justify your proposals by calculating the constants of the corresponding exchange equilibria. Consider possible signs of reactions.

It must be borne in mind that if substances that are sparingly soluble in water (in this case CuS and FeS) are used as a reagent, then reactions involving them must necessarily be accompanied by dissolution, i.e. the products of such reactions should not themselves produce precipitation. For example, it is illiterate to think through the reaction of FeS ↓ and H 2 CO 3 in the hope of obtaining a FeCO 3 precipitate.

Reactions with rich solution SrSO 4 suggest the use of solution over the precipitate, and not the sediment itself.

4. Dependence of pH of solutions on the composition of salts.

Determine the hydrolyzability of the ions of the proposed salts (NH 4 NO 3, KCl, CH 3 COONa, Na 2 CO 3, AlCl 3, CH 3 COONH 4),

· create equations for the hydrolysis of an ion (ions, if both the cation and the anion of the salt are involved in the hydrolysis); calculate the hydrolysis constant ( TO G (Al 3+) take equal to ~10 -5).

write an equation in molecular form

(make a molecular equation based on the predominant ionic reaction ).

· Arrange the salts in order of increasing hydrolyzability.

Test hydrolyzability experimentally. To do this, pour ~1 ml of the corresponding solution into a clean test tube, moisten a glass rod in this solution and apply the solution to indicator paper. Rate according to the color scale approximate value pH of the solution. Why in two cases does the pH correspond to a neutral environment?

5. Medium in solutions of medium and acidic salts.

Make up the equations of the predominant ionic reactions affecting the environment in solutions of potassium ortho-, hydro- and dihydrogen phosphate (K 3 PO 4, K 2 HPO 4, KN 2 PO 4). It must be borne in mind that in solutions of acidic salts, in addition to hydrolysis reactions, dissociation of the anions H 2 PO 4 ‒ and HPO 4 2 ‒ also takes place. The environment will be determined by the predominant reaction. Compare the constants of the competing reactions of hydrolysis and dissociation of anions and draw a conclusion about the pH (more or less than 7). Compare results preliminary analysis with the actual pH value (determine using a universal indicator).

Reference data for preparing for experiments 3, 4, 5

3. Periodic law and periodic system of chemical elements

3.4. Periodic changes 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);
• melting and boiling temperatures of simple substances: when moving from left to right along the period, t pl and t bp initially, in general, increase (diamond is the most refractory substance), and then decrease, which is associated with a change in the structure of simple substances (see above);
• metal and not metallic properties simple substances. Over the period, with increasing Z, the ability of atoms to give up an electron decreases (E and increases), accordingly, the metallic properties of simple substances weaken (non-metallic properties increase, since E avg of atoms increases). From top to bottom in groups A, on the contrary, the metallic properties of simple substances increase, and non-metallic properties weaken;
• composition and acid-base properties of oxides and hydroxides (Table 3.1–3.2).

Table 3.1

Composition of higher oxides and simplest hydrogen compounds of A-group elements

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

As the charge of the atomic nucleus increases in a period, the basic properties of oxides and hydroxides weaken, and the acidic properties increase. The transition from basic oxides and hydroxides to acidic ones in each period occurs gradually, through amphoteric oxides and hydroxides. As an example in table. Figure 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, as the charge of the atomic nucleus increases, the basic properties of oxides and hydroxides increase. For example, for group IIA 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 (alkalies).

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

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

The same trends can be traced for elements of other groups (for the composition and acid-base properties of binary hydrogen compounds, see Table 3.1). In general, with increasing 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 to form an alkali:

NaH + H 2 O = NaOH + H 2,

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

1. In groups A, as the charge of the atomic nucleus increases, 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 ambient conditions. are only hydrogen compounds of elements of groups IVA–VIIA (except H 2 O and HF)

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

Table 3.3

Changes in the properties of atoms of elements and their compounds with increasing charge of the atomic nucleus

Properties	Trend change
	in periods	in groups A
Atomic radius	Decreases	Growing
Ionization energy	Increasing	Decreases
Electron affinity	Increasing	Decreases
Reducing (metallic) properties of atoms	Weaken	Intensifying
Oxidizing (non-metallic) properties of atoms	Intensifying	Weaken
Electronegativity	Increasing	Decreases
Maximum oxidation state	Increasing	Constant
Acidic properties of oxides	Intensifying	Weaken
Acidic properties of hydroxides	Intensifying	Weaken
Acidic properties of hydrogen compounds	Intensifying	Intensifying
Metallic properties of simple substances	Weaken	Intensifying
Non-metallic properties of simple substances	Intensifying	Weaken

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

Solution. The acidic properties of oxides increase from left to right across the period, and weaken from top to bottom across group A. Taking this into account, 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 element anion E 2− has the electronic configuration of an argon atom. Specify the formula of the highest oxide of an element's atom:

Solution. The electronic configuration of the argon atom is 1s 2 2s 2 2p 6 3s 2 3p 6, therefore the electronic configuration of the E atom (the E atom contains 2 electrons less than the E 2− ion) is 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 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 (v.u.) compound of the composition EN 2 (H 2 E):

Solution. Hydrogen compounds of the composition EN 2 (H 2 E) form atoms of elements of groups IIA and VIA, but are volatile at zero conditions. are compounds of group VIA elements, which include sulfur.

Answer: 3).

The characterized trends in changes in the acid-base properties of oxides and hydroxides can be understood based on the analysis of the following simplified diagrams of 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 to form a base increases (according to Coulomb’s law) with increasing charge on the E n + ion. 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 basic 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 oxidation state of the element +n and a decrease in the radius of the E n + ion (this is precisely what is observed with an increase in the charge of the nucleus of an element’s atom from left to right across the period), the E–O bond is strengthened, and the O–H bond is weakened; the process of hydroxide dissociation according to the acid type becomes more probable.

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

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

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

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

ANSWER:

NAndClocated in the same period. Located to the rightN. This means nitrogen is less than carbon.

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

SiAndAllocated in one third period, but to the right isSi, MeansSiless thanAl

The order of increasing atomic sizes 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 nonmetallic properties, since it is located higher and to the right in the periodic table of elements.

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

ANSWER:

The properties of hydroxides vary from acidic to basic. SoH2 CO3 – carbonic acid, as its name suggests, exhibits acidic properties, andPb(OH)2 – 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 the atoms of the elements

	increases
	decreases
	does not change
	changes periodically

ANSWER: 1

We're talking about acids.HF, HCl, HBr, HI. In a rowF, Cl, Br, Ithere is an increase in the size of atoms. Consequently, the internuclear distance increasesH– F, H– Cl, H– Br, H– I. And if so, it means that the bond energy weakens. And a proton is more easily removed in aqueous solutions

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

	germanium

ANSWER: 2

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

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

ANSWER: 1

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
	metallic properties of elements are enhanced
	the highest oxidation state of elements decreases
	weaken the metallic properties of elements

ANSWER: 4

In the period from left to right, non-metallic properties increase, and metallic properties weaken.

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

ANSWER: 4.

Electronegativity is the ability to shift electrons towards itself during the formation chemical bond. Electronegativity is almost directly related to nonmetallic properties. Non-metallic properties decrease, and electronegativity 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. In the series of chemical elements:

boron – carbon – nitrogen

increases

ANSWER:2

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

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

ANSWER: 1

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

A9. Chemical elements are arranged in increasing order of their atomic radius in the series:

ANSWER: 2

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

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

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 are:

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 acidic properties of oxides, like non-metallic properties, increase in periods from left to right

A13. With increasing nuclear charge 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 atomic number

1) intensify

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 increase.

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

1) weakens

2) intensifies

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 increases, therefore, the ability to donate an outer electron increases

A16. In the series Al ®Si ®P ®S

1) the number of electronic layers in atoms increases

2) non-metallic properties are enhanced

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

4) atomic radii increase

ANSWER: 2

In the period with increasing nuclear charge, non-metallic properties increase

A17. In the main subgroups of the periodic table, the reducing ability of atoms of chemical elements increases from

ANSWER: 1

As the number of electronic levels increases, the distance and shielding of outer electrons from the nucleus increases. Consequently, their ability to return (restorative properties) increases.

A18. According to modern concepts, the properties of chemical elements periodically depend on

ANSWER: 3

A19. Atoms of chemical elements having the same number of valence electrons are arranged

	diagonally
	in one group
	in one subgroup
	in one period

ANSWER: 2

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

ANSWER: 3. This element will be located in a 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 O–S–Se–Te series, respectively

	increases, increases
	increases, decreases
	decreases, decreases
	decreases, increases

ANSWER: 3

Electronegativity decreases with increasing number of filled electron layers. Ionization energy is the energy required to remove an electron from an atom. It also decreases

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