To characterize the redox ability of particles, such a concept as the degree of oxidation is important. OXIDATION STATE is the charge that an atom in a molecule or ion could have if all its bonds with other atoms were broken, and the common electron pairs left with more electronegative elements.
Unlike the real-life charges of ions, the oxidation state shows only the conditional charge of an atom in a molecule. It can be negative, positive or zero. For example, the oxidation state of atoms in simple substances ax equals "0" (, 
,
,
). AT chemical compounds atoms can have a constant oxidation state or a variable. For metals of the main subgroups I, II and III groups Periodic system in chemical compounds, the oxidation state is, as a rule, constant and equal to Me +1, Me +2 and Me +3 (Li +, Ca +2, Al +3), respectively. The fluorine atom always has -1. Chlorine in compounds with metals always has -1. In the vast majority of compounds, oxygen has an oxidation state of -2 (except for peroxides, where its oxidation state is -1), and hydrogen +1 (except for metal hydrides, where its oxidation state is -1).
The algebraic sum of the oxidation states of all atoms in a neutral molecule is equal to zero, and in an ion it is equal to the charge of the ion. This relationship makes it possible to calculate the oxidation states of atoms in complex compounds.
In the sulfuric acid molecule H 2 SO 4, the hydrogen atom has an oxidation state of +1, and the oxygen atom is -2. Since there are two hydrogen atoms and four oxygen atoms, we have two "+" and eight "-". Six "+" are missing to neutrality. It is this number that is the oxidation state of sulfur - 
. The potassium dichromate K 2 Cr 2 O 7 molecule consists of two potassium atoms, two chromium atoms and seven oxygen atoms. Potassium has an oxidation state of +1, oxygen has -2. So we have two "+" and fourteen "-". The remaining twelve "+" fall on two chromium atoms, each of which has an oxidation state of +6 ( 
).
Typical oxidizing and reducing agents
From the definition of reduction and oxidation processes, it follows that, in principle, simple and complex substances containing atoms that are not in the lowest oxidation state and therefore can lower their oxidation state can act as oxidizing agents. Similarly, simple and complex substances containing atoms that are not in the highest oxidation state and therefore can increase their oxidation state can act as reducing agents.
The strongest oxidizing agents are:
1) simple substances formed by atoms having a large electronegativity, i.e. typical non-metals located in the main subgroups of the sixth and seventh groups of the periodic system: F, O, Cl, S (respectively F 2 , O 2 , Cl 2 , S);
2) substances containing elements in higher and intermediate
positive oxidation states, including in the form of ions, both simple, elemental (Fe 3+) and oxygen-containing, oxoanions (permanganate ion - MnO 4 -);
3) peroxide compounds.
Specific substances used in practice as oxidizers are oxygen and ozone, chlorine, bromine, permanganates, dichromates, oxyacids of chlorine and their salts (for example, 
,
,
), Nitric acid ( 
), concentrated sulfuric acid ( 
), manganese dioxide ( 
), hydrogen peroxide and metal peroxides ( 
,
).
The most powerful reducing agents are:
1) simple substances whose atoms have low electronegativity (“active metals”);
2) metal cations in low oxidation states (Fe 2+);
3) simple elemental anions, for example, sulfide ion S 2- ;
4) oxygen-containing anions (oxoanions) corresponding to the lowest positive oxidation states of the element (nitrite 
, sulfite 
).
Specific substances used in practice as reducing agents are, for example, alkali and alkaline earth metals, sulfides, sulfites, hydrogen halides (except HF), organic substances - alcohols, aldehydes, formaldehyde, glucose, oxalic acid, as well as hydrogen, carbon, monoxide carbon ( 
) and aluminum at high temperatures.
In principle, if a substance contains an element in an intermediate oxidation state, then these substances can exhibit both oxidizing and reducing properties. It all depends on
"partner" in the reaction: with a sufficiently strong oxidizing agent, it can react as a reducing agent, and with a sufficiently strong reducing agent, as an oxidizing agent. So, for example, the nitrite ion NO 2 - in an acidic environment acts as an oxidizing agent with respect to the ion I -:
2
+
2
+ 4HCl→ 
+
2
+ 4KCl + 2H 2 O
and as a reducing agent in relation to the permanganate ion MnO 4 -
5
+
2
+ 3H 2 SO 4 → 2 
+
5
+ K 2 SO 4 + 3H 2 O
Part I
1. The oxidation state (s. o.) is conditional charge of the atoms of a chemical element in a complex substance, calculated on the basis of the assumption that it consists of simple ions.
Should know!
1) In connections with. about. hydrogen = +1, except for hydrides.
2) In compounds with. about. oxygen = -2, except for peroxides 
and fluorides
3) The oxidation state of metals is always positive.
For metals of the main subgroups first three groups with. about. constant:
Group IA metals - p. about. = +1,
Group IIA metals - p. about. = +2,
Group IIIA metals - p. about. = +3.
4) For free atoms and simple substances p. about. = 0.
5) Total s. about. all elements in the compound = 0.
2. Method of formation of names two-element (binary) compounds.
4. Complete the table "Names and formulas of binary compounds."
5. Determine the degree of oxidation of the highlighted element of the complex compound.
Part II
1. Determine the oxidation states chemical elements in compounds according to their formulas. Write down the names of these substances.
2. Separate substances FeO, Fe2O3, CaCl2, AlBr3, CuO, K2O, BaCl2, SO3into two groups. Write down the names of substances, indicating the degree of oxidation.
3. Establish a correspondence between the name and oxidation state of an atom of a chemical element and the formula of the compound.
4. Make formulas of substances by name.
5. How many molecules are contained in 48 g of sulfur oxide (IV)?
6. Using the Internet and other sources of information, prepare a report on the use of any binary connection according to the following plan:
1) formula;
2) name;
3) properties;
4) application.
H2O water, hydrogen oxide.
Water at normal conditions liquid, colorless, odorless, in a thick layer - blue. The boiling point is about 100⁰С. It is a good solvent. A water molecule consists of two hydrogen atoms and one oxygen atom, this is its qualitative and quantitative composition. This is complex substance, it is characterized by the following Chemical properties: interaction with alkali metals, alkaline earth metals. Exchange reactions with water are called hydrolysis. These reactions have great importance in chemistry.
7. The oxidation state of manganese in the K2MnO4 compound is:
3) +6
8. Chromium has the lowest oxidation state in a compound whose formula is:
1) Cr2O3
9. Chlorine exhibits the maximum oxidation state in a compound whose formula is:
3) Сl2O7
DEFINITION
Oxidation state is a quantitative assessment of the state of an atom of a chemical element in a compound, based on its electronegativity.
It takes both positive and negative values. To indicate the oxidation state of an element in a compound, you need to put an Arabic numeral with the corresponding sign ("+" or "-") above its symbol.
It should be remembered that the degree of oxidation is a quantity that does not have physical sense, since it does not reflect the real charge of the atom. However, this concept is very widely used in chemistry.
Table of the oxidation state of chemical elements
The maximum positive and minimum negative oxidation states can be determined using the Periodic Table of D.I. Mendeleev. They are equal to the number of the group in which the element is located, and the difference between the value of the "highest" oxidation state and the number 8, respectively.
If we consider chemical compounds more specifically, then in substances with non-polar bonds, the oxidation state of the elements is zero (N 2, H 2, Cl 2).
The oxidation state of metals in the elementary state is zero, since the distribution of electron density in them is uniform.
In simple ionic compounds, the oxidation state of their constituent elements is electric charge, since during the formation of these compounds there is an almost complete transition of electrons from one atom to another: Na +1 I -1, Mg +2 Cl -1 2, Al +3 F -1 3, Zr +4 Br -1 4.
When determining the degree of oxidation of elements in compounds with polar covalent bonds, the values of their electronegativity are compared. Since, during the formation of a chemical bond, electrons are displaced to atoms of more electronegative elements, the latter have a negative oxidation state in compounds.
There are elements for which only one value of the oxidation state is characteristic (fluorine, metals of IA and IIA groups, etc.). Fluorine, characterized highest value electronegativity, in compounds it always has a constant negative oxidation state (-1).
Alkaline and alkaline earth elements, which are characterized by a relatively low value of electronegativity, always have a positive oxidation state, equal to (+1) and (+2), respectively.
However, there are also such chemical elements, which are characterized by several values of the degree of oxidation (sulfur - (-2), 0, (+2), (+4), (+6), etc.).
In order to make it easier to remember how many and what oxidation states are characteristic of a particular chemical element, tables of the oxidation states of chemical elements are used, which look like this:
|
Serial number |
Russian / English title |
chemical symbol |
Oxidation state |
|
Hydrogen |
|||
|
Helium / Helium |
|||
|
Lithium / Lithium |
|||
|
Beryllium / Beryllium |
|||
|
(-1), 0, (+1), (+2), (+3) |
|||
|
Carbon / Carbon |
(-4), (-3), (-2), (-1), 0, (+2), (+4) |
||
|
Nitrogen / Nitrogen |
(-3), (-2), (-1), 0, (+1), (+2), (+3), (+4), (+5) |
||
|
Oxygen / Oxygen |
(-2), (-1), 0, (+1), (+2) |
||
|
Fluorine / Fluorine |
|||
|
Sodium |
|||
|
Magnesium / Magnesium |
|||
|
Aluminum |
|||
|
Silicon / Silicon |
(-4), 0, (+2), (+4) |
||
|
Phosphorus / Phosphorus |
(-3), 0, (+3), (+5) |
||
|
Sulfur |
(-2), 0, (+4), (+6) |
||
|
Chlorine / Chlorine |
(-1), 0, (+1), (+3), (+5), (+7), rarely (+2) and (+4) |
||
|
Argon / Argon |
|||
|
Potassium / Potassium |
|||
|
Calcium / Calcium |
|||
|
Scandium / Scandium |
|||
|
Titanium / Titanium |
(+2), (+3), (+4) |
||
|
Vanadium / Vanadium |
(+2), (+3), (+4), (+5) |
||
|
Chromium / Chromium |
(+2), (+3), (+6) |
||
|
Manganese / Manganese |
(+2), (+3), (+4), (+6), (+7) |
||
|
Iron / Iron |
(+2), (+3), rarely (+4) and (+6) |
||
|
Cobalt / Cobalt |
(+2), (+3), rarely (+4) |
||
|
Nickel / Nickel |
(+2), rarely (+1), (+3) and (+4) |
||
|
Copper |
+1, +2, rare (+3) |
||
|
Gallium / Gallium |
(+3), rare (+2) |
||
|
Germanium / Germanium |
(-4), (+2), (+4) |
||
|
Arsenic / Arsenic |
(-3), (+3), (+5), rarely (+2) |
||
|
Selenium / Selenium |
(-2), (+4), (+6), rarely (+2) |
||
|
Bromine / Bromine |
(-1), (+1), (+5), rarely (+3), (+4) |
||
|
Krypton / Krypton |
|||
|
Rubidium / Rubidium |
|||
|
Strontium / Strontium |
|||
|
Yttrium / Yttrium |
|||
|
Zirconium / Zirconium |
(+4), rarely (+2) and (+3) |
||
|
Niobium / Niobium |
(+3), (+5), rarely (+2) and (+4) |
||
|
Molybdenum / Molybdenum |
(+3), (+6), rarely (+2), (+3) and (+5) |
||
|
Technetium / Technetium |
|||
|
Ruthenium / Ruthenium |
(+3), (+4), (+8), rarely (+2), (+6) and (+7) |
||
|
Rhodium |
(+4), rarely (+2), (+3) and (+6) |
||
|
Palladium / Palladium |
(+2), (+4), rarely (+6) |
||
|
Silver / Silver |
(+1), rarely (+2) and (+3) |
||
|
Cadmium / Cadmium |
(+2), rare (+1) |
||
|
Indium / Indium |
(+3), rarely (+1) and (+2) |
||
|
Tin / Tin |
(+2), (+4) |
||
|
Antimony / Antimony |
(-3), (+3), (+5), rarely (+4) |
||
|
Tellurium / Tellurium |
(-2), (+4), (+6), rarely (+2) |
||
|
(-1), (+1), (+5), (+7), rarely (+3), (+4) |
|||
|
Xenon / Xenon |
|||
|
Cesium / Cesium |
|||
|
Barium / Barium |
|||
|
Lanthanum / Lanthanum |
|||
|
Cerium / Cerium |
(+3), (+4) |
||
|
Praseodymium / Praseodymium |
|||
|
Neodymium / Neodymium |
(+3), (+4) |
||
|
Promethium / Promethium |
|||
|
Samaria / Samarium |
(+3), rare (+2) |
||
|
Europium / Europium |
(+3), rare (+2) |
||
|
Gadolinium / Gadolinium |
|||
|
Terbium / Terbium |
(+3), (+4) |
||
|
Dysprosium / Dysprosium |
|||
|
Holmium / Holmium |
|||
|
Erbium / Erbium |
|||
|
Thulium / Thulium |
(+3), rare (+2) |
||
|
Ytterbium / Ytterbium |
(+3), rare (+2) |
||
|
Lutetium / Lutetium |
|||
|
Hafnium / Hafnium |
|||
|
Tantalum / Tantalum |
(+5), rarely (+3), (+4) |
||
|
Tungsten / Tungsten |
(+6), rare (+2), (+3), (+4) and (+5) |
||
|
Rhenium / Rhenium |
(+2), (+4), (+6), (+7), rare (-1), (+1), (+3), (+5) |
||
|
Osmium / Osmium |
(+3), (+4), (+6), (+8), rarely (+2) |
||
|
Iridium / Iridium |
(+3), (+4), (+6), rarely (+1) and (+2) |
||
|
Platinum / Platinum |
(+2), (+4), (+6), rarely (+1) and (+3) |
||
|
Gold / Gold |
(+1), (+3), rarely (+2) |
||
|
Mercury / Mercury |
(+1), (+2) |
||
|
Waist / Thallium |
(+1), (+3), rarely (+2) |
||
|
Lead / Lead |
(+2), (+4) |
||
|
Bismuth / Bismuth |
(+3), rarely (+3), (+2), (+4) and (+5) |
||
|
Polonium / Polonium |
(+2), (+4), rarely (-2) and (+6) |
||
|
Astatine / Astatine |
|||
|
Radon / Radon |
|||
|
Francium / Francium |
|||
|
Radium / Radium |
|||
|
Actinium / Actinium |
|||
|
Thorium / Thorium |
|||
|
Proactinium / Protactinium |
|||
|
Uranus / Uranium |
(+3), (+4), (+6), rarely (+2) and (+5) |
Examples of problem solving
EXAMPLE 1
- The oxidation state of phosphorus in phosphine is (-3), and in phosphoric acid - (+5). Change in the oxidation state of phosphorus: +3 → +5, i.e. the first answer.
- The oxidation state of a chemical element in a simple substance is zero. The oxidation state of phosphorus in the oxide composition P 2 O 5 is equal to (+5). Change in the oxidation state of phosphorus: 0 → +5, i.e. third answer.
- The oxidation state of phosphorus in an acid of composition HPO 3 is (+5), and H 3 PO 2 is (+1). Change in the oxidation state of phosphorus: +5 → +1, i.e. fifth answer.
EXAMPLE 2
| Exercise | The oxidation state (-3) carbon has in the compound: a) CH 3 Cl; b) C 2 H 2 ; c) HCOH; d) C 2 H 6 . |
| Decision | In order to give a correct answer to the question posed, we will alternately determine the degree of carbon oxidation in each of the proposed compounds. a) the oxidation state of hydrogen is (+1), and chlorine - (-1). We take for "x" the degree of oxidation of carbon: x + 3×1 + (-1) =0; The answer is incorrect. b) the oxidation state of hydrogen is (+1). We take for "y" the degree of oxidation of carbon: 2×y + 2×1 = 0; The answer is incorrect. c) the oxidation state of hydrogen is (+1), and oxygen - (-2). Let's take for "z" the oxidation state of carbon: 1 + z + (-2) +1 = 0: The answer is incorrect. d) the oxidation state of hydrogen is (+1). Let's take for "a" the oxidation state of carbon: 2×a + 6×1 = 0; Correct answer. |
| Answer | Option (d) |
Video lesson 2: The degree of oxidation of chemical elements
Video lesson 3: Valence. Definition of valence
Lecture: Electronegativity. The oxidation state and valency of chemical elements
Electronegativity
Electronegativity- this is the ability of atoms to attract the electrons of other atoms to themselves to connect with them.
It is easy to judge the electronegativity of a chemical element from the table. Remember, in one of our lessons it was said that it increases when moving from left to right through periods in the periodic table and moving from bottom to top in groups.
For example, given the task to determine which element from the proposed series is the most electronegative: C (carbon), N (nitrogen), O (oxygen), S (sulfur)? We look at the table and find that this is O, because it is to the right and above the rest.
What factors affect electronegativity? This is:
- The radius of an atom, the smaller it is, the higher the electronegativity.
- The filling of the valence shell with electrons, the more of them, the higher the electronegativity.
Of all the chemical elements, fluorine is the most electronegative, because it has a small atomic radius and 7 electrons in the valence shell.
Elements with low electronegativity include alkaline and alkaline earth metals. They have large radii and very few electrons in the outer shell.
The values of the electronegativity of an atom cannot be constant, because it depends on many factors, including those listed above, as well as the degree of oxidation, which can be different for the same element. Therefore, it is customary to talk about the relativity of electronegativity values. You can use the following scales:
You will need electronegativity values when writing formulas for binary compounds consisting of two elements. For example, the formula for copper oxide is Cu 2 O - the first element should be the one whose electronegativity is lower.
At the moment of formation of a chemical bond, if the difference in electronegativity between the elements is greater than 2.0, a covalent polar bond is formed, if less, an ionic one.
Oxidation state
Oxidation state (CO)- this is the conditional or real charge of the atom in the compound: conditional - if the bond is covalent polar, real - if the bond is ionic.
An atom acquires a positive charge when it donates electrons, and a negative charge when it receives electrons.
The oxidation states are written above the signed symbols «+»/«-» . There are also intermediate COs. The maximum CO of the element is positive and equal to the group number, and the minimum negative for metals is zero, for non-metals = (group number - 8). Elements with a maximum CO only accept electrons, and with a minimum, they only give them away. Elements that have intermediate COs can both donate and accept electrons.
Consider some of the rules that should be followed to determine the CO:
CO of all simple substances is equal to zero.
The sum of all CO atoms in the molecule is also equal to zero, since any molecule is electrically neutral.
In compounds with a covalent non-polar bond, CO is zero (O 2 0), and with an ionic bond it is equal to the charges of the ions (Na + Cl - CO sodium +1, chlorine -1). CO elements of compounds with a covalent polar bond are considered as with an ionic bond (H:Cl \u003d H + Cl -, hence H +1 Cl -1).
The elements in a compound that have the highest electronegativity have negative oxidation states if the least are positive. Based on this, we can conclude that metals have only a “+” oxidation state.
Constant oxidation states:
Hydrogen +1. Exception: hydrides active metals NaH, CaH 2, etc., where the oxidation state of hydrogen is -1.
Oxygen -2. Exception: F 2 -1 O +2 and peroxides that contain the –О–О– group, in which the oxidation state of oxygen is –1.
Alkali metals +1.
All metals of the second group +2. Exception: Hg +1, +2.
Aluminum +3.
When an ionic bond is formed, there is a certain transition of an electron, from a less electronegative atom to an atom of greater electronegativity. Also, in this process, atoms always lose their electrical neutrality and subsequently turn into ions. Integer charges are formed in the same way. When a covalent polar bond is formed, the electron transfers only partially, so partial charges arise.
ValenceValenceis the ability of atoms to form n - the number chemical bonds with atoms of other elements.
And valency is the ability of an atom to keep other atoms near it. As you know from school course chemistry, different atoms bind to each other by electrons of the outer energy level. An unpaired electron seeks a pair for itself from another atom. These outer level electrons are called valence electrons. This means that valence can also be defined as the number of electron pairs that bind atoms to each other. look structural formula water: H - O - N. Each dash is an electron pair, which means it shows valency, i.e. oxygen here has two dashes, which means it is divalent, one dash comes from hydrogen molecules, which means hydrogen is monovalent. When writing, valency is indicated by Roman numerals: O (II), H (I). It can also be placed above an element.
Valence is either constant or variable. For example, in alkali metals, it is constant and equals I. But chlorine in various compounds exhibits valences I, III, V, VII.
How to determine the valency of an element?
Let's turn again to Periodic table. The metals of the main subgroups have a constant valence, so the metals of the first group have a valence of I, the second of II. And for metals of secondary subgroups, the valency is variable. It is also variable for non-metals. The highest valence of an atom is equal to the group number, the lowest is = group number - 8. A familiar wording. Does this mean that the valency coincides with the oxidation state. Remember, valence may coincide with the degree of oxidation, but these indicators are not identical to each other. Valency cannot have the =/- sign, and also cannot be zero.
The second way to determine valence by chemical formula if the constant valency of one of the elements is known. For example, take the formula for copper oxide: CuO. Oxygen valency II. We see that there is one copper atom per oxygen atom in this formula, which means that the valency of copper is II. Now let's take a more complicated formula: Fe 2 O 3. The valency of the oxygen atom is II. There are three such atoms here, we multiply 2 * 3 \u003d 6. We found that there are 6 valences for two iron atoms. Let's find out the valency of one iron atom: 6:2=3. So the valency of iron is III.
In addition, when it is necessary to evaluate the "maximum valence", one should always proceed from electronic configuration, which is present in the "excited" state.
| | |
Modern wording Periodic Law, discovered by D. I. Mendeleev in 1869:
The properties of the elements are in a periodic dependence on the ordinal number.
Periodically recurring nature of composition change electron shell atoms of elements explains periodic change properties of elements when moving through periods and groups of the Periodic system.
Let us trace, for example, the change in the higher and lower oxidation states of the elements of the IA - VIIA groups in the second - fourth periods according to Table. 3.
Positive oxidation states are exhibited by all elements, with the exception of fluorine. Their values increase with increasing nuclear charge and coincide with the number of electrons at the last energy level (except for oxygen). These oxidation states are called higher oxidation states. For example, the highest oxidation state of phosphorus P is +V.
Negative oxidation states are exhibited by elements starting with carbon C, silicon Si and germanium Ge. Their values are equal to the number of electrons missing up to eight. These oxidation states are called inferior oxidation states. For example, the phosphorus atom P at the last energy level lacks three electrons to eight, which means that the lowest oxidation state of phosphorus P is -III.
The values of higher and lower oxidation states are repeated periodically, coinciding in groups; for example, in the IVA group, carbon C, silicon Si and germanium Ge have the highest oxidation state +IV, and the lowest oxidation state - IV.
This frequency of changes in oxidation states is reflected in the periodic change in the composition and properties of chemical compounds of elements.
Similarly, a periodic change in the electronegativity of elements in the 1st-6th periods of the IA–VIIA groups can be traced (Table 4).
In each period of the Periodic Table, the electronegativity of the elements increases with increasing serial number (from left to right).
In each group In the periodic table, electronegativity decreases as the atomic number increases (from top to bottom). Fluorine F has the highest, and cesium Cs the lowest electronegativity among the elements of the 1st-6th periods.
Typical non-metals have high electronegativity, while typical metals have low electronegativity.
Examples of tasks of parts A, B1. In the 4th period, the number of elements is
2. Metallic properties of elements of the 3rd period from Na to Cl
1) force
2) weaken
3) do not change
4) don't know
3. Non-metallic properties of halogens with increasing atomic number
1) increase
2) go down
3) remain unchanged
4) don't know
4. In the series of elements Zn - Hg - Co - Cd, one element that is not included in the group is
5. The metallic properties of the elements increase in a row
1) In-Ga-Al
2) K - Rb - Sr
3) Ge-Ga-Tl
4) Li - Be - Mg
6. Non-metallic properties in the series of elements Al - Si - C - N
1) increase
2) decrease
3) do not change
4) don't know
7. In the series of elements O - S - Se - Te, the dimensions (radii) of the atom
1) decrease
2) increase
3) do not change
4) don't know
8. In the series of elements P - Si - Al - Mg, the dimensions (radii) of the atom
1) decrease
2) increase
3) do not change
4) don't know
9. For phosphorus, the element with lesser electronegativity is
10. A molecule in which the electron density is shifted to the phosphorus atom is
11. Supreme the oxidation state of the elements is manifested in a set of oxides and fluorides
1) СlO 2, PCl 5, SeCl 4, SO 3
2) PCl, Al 2 O 3, KCl, CO
3) SeO 3, BCl 3, N 2 O 5, CaCl 2
4) AsCl 5 , SeO 2 , SCl 2 , Cl 2 O 7
12. Inferior the degree of oxidation of elements - in their hydrogen compounds and fluorides of the set
1) ClF 3 , NH 3 , NaH, OF 2
2) H 3 S +, NH+, SiH 4, H 2 Se
3) CH 4 , BF 4 , H 3 O + , PF 3
4) PH 3 , NF+, HF 2 , CF 4
13. Valence for a polyvalent atom the same in a series of compounds
1) SiH 4 - AsH 3 - CF 4
2) PH 3 - BF 3 - ClF 3
3) AsF 3 - SiCl 4 - IF 7
4) H 2 O - BClg - NF 3
14. Indicate the correspondence between the formula of a substance or ion and the degree of oxidation of carbon in them
