Elements with constant oxidation states table. Chemistry preparation for fever and dpa comprehensive edition

The chemical element in a compound, calculated from the assumption that all bonds are ionic.

Oxidation states can have a positive, negative or zero value, therefore the algebraic sum of the oxidation states of elements in a molecule, taking into account the number of their atoms, is equal to 0, and in an ion - the charge of the ion.

1. The oxidation states of metals in compounds are always positive.

2. The highest oxidation state corresponds to the number of the group of the periodic table where the element is located (exceptions are: Au +3(I group), Cu +2(II), from group VIII the oxidation state +8 can only be found in osmium Os and ruthenium Ru.

3. The oxidation states of non-metals depend on which atom it is connected to:

if with a metal atom, then the oxidation state is negative;
if with a non-metal atom, then the oxidation state can be either positive or negative. It depends on the electronegativity of the atoms of the elements.

4. The highest negative oxidation state of non-metals can be determined by subtracting from 8 the number of the group in which the element is located, i.e. the highest positive oxidation state is equal to the number of electrons in the outer layer, which corresponds to the group number.

5. The oxidation states of simple substances are 0, regardless of whether it is a metal or a non-metal.

Elements with constant oxidation states.

Element	Characteristic oxidation state	Exceptions
		Metal hydrides: LIH -1

		Oxidation state called the conditional charge of a particle under the assumption that the bond is completely broken (has an ionic character). H- Cl = H + + Cl - , The bond in hydrochloric acid is polar covalent. The electron pair is more shifted towards the atom Cl - , because it is a more electronegative element. How to determine the oxidation state? Electronegativity is the ability of atoms to attract electrons from other elements. The oxidation number is indicated above the element: Br 2 0 , Na 0 , O +2 F 2 -1 ,K + Cl - etc. It can be negative and positive. The oxidation state of a simple substance (unbound, free state) is zero. The oxidation state of oxygen for most compounds is -2 (the exception is peroxides H 2 O 2, where it is equal to -1 and compounds with fluorine - O +2 F 2 -1 , O 2 +1 F 2 -1 ). - Oxidation state of a simple monatomic ion is equal to its charge: Na + , Ca +2 . Hydrogen in its compounds has an oxidation state of +1 (exceptions are hydrides - Na + H - and type connections C +4 H 4 -1 ). In metal-nonmetal bonds, the negative oxidation state is that atom that has greater electronegativity (data on electronegativity are given in the Pauling scale): H + F - , Cu + Br - , Ca +2 (NO 3 ) - etc. Rules for determining the degree of oxidation in chemical compounds. Let's take the connection KMnO 4 , it is necessary to determine the oxidation state of the manganese atom. Reasoning: Potassium is an alkali metal in Group I of the periodic table, and therefore has only a positive oxidation state of +1. Oxygen, as is known, in most of its compounds has an oxidation state of -2. This substance is not a peroxide, which means it is no exception. Makes up the equation: K+Mn X O 4 -2 Let X- unknown to us oxidation state of manganese. The number of potassium atoms is 1, manganese - 1, oxygen - 4. It has been proven that the molecule as a whole is electrically neutral, so its total charge must be zero. 1(+1) + 1(X) + 4(-2) = 0, X = +7, This means that the oxidation state of manganese in potassium permanganate = +7. Let's take another example of an oxide Fe2O3. It is necessary to determine the oxidation state of the iron atom. Reasoning: Iron is a metal, oxygen is a non-metal, which means that oxygen will be an oxidizing agent and have a negative charge. We know that oxygen has an oxidation state of -2. We count the number of atoms: iron - 2 atoms, oxygen - 3. We create an equation where X- oxidation state of the iron atom: 2(X) + 3(-2) = 0, Conclusion: the oxidation state of iron in this oxide is +3. Examples. Determine the oxidation states of all atoms in the molecule. 1. K2Cr2O7. Oxidation state K +1, oxygen O -2. Given indexes: O=(-2)×7=(-14), K=(+1)×2=(+2). Because the algebraic sum of the oxidation states of elements in a molecule, taking into account the number of their atoms, is equal to 0, then the number of positive oxidation states is equal to the number of negative ones. Oxidation states K+O=(-14)+(+2)=(-12). It follows from this that the chromium atom has 12 positive powers, but there are 2 atoms in the molecule, which means there are (+12) per atom: 2 = (+6). Answer: K 2 + Cr 2 +6 O 7 -2. 2.(AsO 4) 3- . In this case, the sum of oxidation states will no longer be equal to zero, but to the charge of the ion, i.e. - 3. Let's make an equation: x+4×(- 2)= - 3 . Answer: (As +5 O 4 -2) 3- .

Many school textbooks and manuals teach how to create formulas based on valencies, even for compounds with ionic bonds. To simplify the procedure for drawing up formulas, this, in our opinion, is acceptable. But you need to understand that this is not entirely correct due to the above reasons.

A more universal concept is the concept of oxidation state. Using the values of the oxidation states of atoms, as well as the valency values, you can compose chemical formulas and write down formula units.

Oxidation state- this is the conditional charge of an atom in a particle (molecule, ion, radical), calculated in the approximation that all bonds in the particle are ionic.

Before determining oxidation states, it is necessary to compare the electronegativity of the bonded atoms. An atom with a higher electronegativity value has a negative oxidation state, and an atom with a lower electronegativity has a positive oxidation state.

In order to objectively compare the electronegativity values of atoms when calculating oxidation states, in 2013 IUPAC recommended using the Allen scale.

* So, for example, according to the Allen scale, the electronegativity of nitrogen is 3.066, and chlorine is 2.869.

Let us illustrate the above definition with examples. Let's compose the structural formula of a water molecule.

Covalent polar O-H bonds are indicated in blue.

Let's imagine that both bonds are not covalent, but ionic. If they were ionic, then one electron would transfer from each hydrogen atom to the more electronegative oxygen atom. Let's denote these transitions with blue arrows.

*In thatexample, the arrow serves to visually illustrate the complete transfer of electrons, and not to illustrate the inductive effect.

It is easy to notice that the number of arrows shows the number of electrons transferred, and their direction indicates the direction of electron transfer.

There are two arrows directed at the oxygen atom, which means that two electrons are transferred to the oxygen atom: 0 + (-2) = -2. A charge of -2 is formed on the oxygen atom. This is the oxidation state of oxygen in a water molecule.

Each hydrogen atom loses one electron: 0 - (-1) = +1. This means that hydrogen atoms have an oxidation state of +1.

The sum of oxidation states always equals the total charge of the particle.

For example, the sum of oxidation states in a water molecule is equal to: +1(2) + (-2) = 0. The molecule is an electrically neutral particle.

If we calculate the oxidation states in an ion, then the sum of the oxidation states is, accordingly, equal to its charge.

The oxidation state value is usually indicated in the upper right corner of the element symbol. Moreover, the sign is written in front of the number. If the sign comes after the number, then this is the charge of the ion.

For example, S -2 is a sulfur atom in the oxidation state -2, S 2- is a sulfur anion with a charge of -2.

S +6 O -2 4 2- - values of the oxidation states of atoms in the sulfate anion (the charge of the ion is highlighted in green).

Now consider the case when the compound has mixed bonds: Na 2 SO 4. The bond between the sulfate anion and sodium cations is ionic, the bonds between the sulfur atom and the oxygen atoms in the sulfate ion are covalent polar. Let's write down the graphic formula of sodium sulfate, and use arrows to indicate the direction of electron transition.

*Structural formula displays the order of covalent bonds in a particle (molecule, ion, radical). Structural formulas are used only for particles with covalent bonds. For particles with ionic bonds, the concept of a structural formula has no meaning. If the particle contains ionic bonds, then a graphical formula is used.

We see that six electrons leave the central sulfur atom, which means the oxidation state of sulfur is 0 - (-6) = +6.

The terminal oxygen atoms each take two electrons, which means their oxidation states are 0 + (-2) = -2

The bridging oxygen atoms each accept two electrons and have an oxidation state of -2.

It is also possible to determine the degree of oxidation using a structural-graphical formula, where covalent bonds are indicated by dashes, and the charge of ions is indicated.

In this formula, the bridging oxygen atoms already have single negative charges and an additional electron comes to them from the sulfur atom -1 + (-1) = -2, which means their oxidation states are equal to -2.

The degree of oxidation of sodium ions is equal to their charge, i.e. +1.

Let us determine the degree of oxidation of elements in potassium superoxide (superoxide). To do this, let’s create a graphical formula for potassium superoxide and show the redistribution of electrons with an arrow. The O-O bond is a covalent non-polar bond, so it does not indicate the redistribution of electrons.

* Superoxide anion is a radical ion. The formal charge of one oxygen atom is -1, and the other, with an unpaired electron, is 0.

We see that the oxidation state of potassium is +1. The oxidation state of the oxygen atom written opposite potassium in the formula is -1. The oxidation state of the second oxygen atom is 0.

In the same way, you can determine the degree of oxidation using the structural-graphic formula.

The circles indicate the formal charges of the potassium ion and one of the oxygen atoms. In this case, the values of formal charges coincide with the values of oxidation states.

Since both oxygen atoms in the superoxide anion have different oxidation states, we can calculate arithmetic mean oxidation state oxygen.

It will be equal to / 2 = - 1/2 = -0.5.

Values for arithmetic mean oxidation states are usually indicated in gross formulas or formula units to show that the sum of the oxidation states is equal to the total charge of the system.

For the case with superoxide: +1 + 2(-0.5) = 0

It is easy to determine oxidation states using electron-dot formulas, in which lone electron pairs and electrons of covalent bonds are indicated by dots.

Oxygen is an element of group VIA, therefore its atom has 6 valence electrons. Let's imagine that the bonds in a water molecule are ionic, in this case the oxygen atom would receive an octet of electrons.

The oxidation state of oxygen is correspondingly equal to: 6 - 8 = -2.

A hydrogen atoms: 1 - 0 = +1

The ability to determine oxidation states using graphic formulas is invaluable for understanding the essence of this concept; this skill will also be required in a course in organic chemistry. If we are dealing with inorganic substances, then it is necessary to be able to determine oxidation states using molecular formulas and formula units.

To do this, first of all you need to understand that oxidation states can be constant and variable. Elements exhibiting constant oxidation states must be remembered.

Any chemical element is characterized by higher and lower oxidation states.

Lowest oxidation state- this is the charge that an atom acquires as a result of receiving the maximum number of electrons on the outer electron layer.

In view of this, the lowest oxidation state has a negative value, with the exception of metals, whose atoms never accept electrons due to low electronegativity values. Metals have a lowest oxidation state of 0.

Most nonmetals of the main subgroups try to fill their outer electron layer with up to eight electrons, after which the atom acquires a stable configuration ( octet rule). Therefore, in order to determine the lowest oxidation state, it is necessary to understand how many valence electrons an atom lacks to reach the octet.

For example, nitrogen is a group VA element, which means that the nitrogen atom has five valence electrons. The nitrogen atom is three electrons short of the octet. This means the lowest oxidation state of nitrogen is: 0 + (-3) = -3

In chemical processes, the main role is played by atoms and molecules, the properties of which determine the outcome of chemical reactions. One of the important characteristics of an atom is the oxidation number, which simplifies the method of accounting for electron transfer in a particle. How to determine the oxidation state or formal charge of a particle and what rules do you need to know for this?

Any chemical reaction is caused by the interaction of atoms of different substances. The reaction process and its result depend on the characteristics of the smallest particles.

The term oxidation (oxidation) in chemistry means a reaction during which a group of atoms or one of them loses electrons or gains; in the case of acquisition, the reaction is called “reduction”.

The oxidation state is a quantity that is measured quantitatively and characterizes the redistributed electrons during a reaction. Those. During the process of oxidation, electrons in an atom decrease or increase, redistributing between other interacting particles, and the level of oxidation shows exactly how they are reorganized. This concept is closely related to the electronegativity of particles - their ability to attract and repel free ions.

Determining the level of oxidation depends on the characteristics and properties of a particular substance, so the calculation procedure cannot be unambiguously called easy or complex, but its results help conditionally record the processes of redox reactions. It should be understood that the resulting calculation result is the result of taking into account the transfer of electrons and has no physical meaning, and is not the true charge of the nucleus.

It is important to know! Inorganic chemistry often uses the term valence instead of the oxidation state of elements; this is not a mistake, but it should be borne in mind that the second concept is more universal.

The concepts and rules for calculating the movement of electrons are the basis for classifying chemical substances (nomenclature), describing their properties and drawing up communication formulas. But most often this concept is used to describe and work with redox reactions.

Rules for determining the degree of oxidation

How to find out the oxidation state? When working with redox reactions, it is important to know that the formal charge of a particle will always be equal to the value of the electron, expressed in a numerical value. This feature is due to the assumption that the electron pairs forming a bond are always completely shifted towards more negative particles. It should be understood that we are talking about ionic bonds, and in the case of a reaction, electrons will be divided equally between identical particles.

The oxidation number can have both positive and negative values. The thing is that during the reaction the atom must become neutral, and for this it is necessary to either add a certain number of electrons to the ion, if it is positive, or take them away if it is negative. To denote this concept, when writing a formula, an Arabic numeral with the corresponding sign is usually written above the element designation. For example, or etc.

You should know that the formal charge of metals will always be positive, and in most cases, you can use the periodic table to determine it. There are a number of features that must be taken into account in order to determine the indicators correctly.

Oxidation degree:

Having remembered these features, it will be quite simple to determine the oxidation number of elements, regardless of the complexity and number of atomic levels.

Useful video: determining the oxidation state

Mendeleev's periodic table contains almost all the necessary information for working with chemical elements. For example, schoolchildren use only it to describe chemical reactions. So, in order to determine the maximum positive and negative values of the oxidation number, you need to check the designation of the chemical element in the table:

The maximum positive is the number of the group in which the element is located.
The maximum negative oxidation state is the difference between the maximum positive boundary and the number 8.

Thus, it is enough to simply find out the extreme boundaries of the formal charge of a particular element. This action can be performed using calculations based on the periodic table.

It is important to know! One element can simultaneously have several different oxidation rates.

There are two main methods for determining the level of oxidation, examples of which are presented below. The first of them is a method that requires knowledge and ability to apply the laws of chemistry. How to arrange oxidation states using this method?

Rule for determining oxidation states

To do this you need:

Determine whether a given substance is elemental and whether it is outside the bond. If so, then its oxidation number will be 0, regardless of the composition of the substance (individual atoms or multi-level atomic compounds).
Determine whether the substance in question consists of ions. If so, then the degree of oxidation will be equal to their charge.
If the substance in question is metal, then look at the indicators of other substances in the formula and calculate the metal readings using arithmetic operations.
If the entire compound has one charge (essentially it is the sum of all particles of the elements represented), then it is enough to determine the indicators of simple substances, then subtract them from the total and get the metal data.
If the relationship is neutral, then the total sum must be zero.

As an example, consider combining with an aluminum ion whose net charge is zero. The rules of chemistry confirm the fact that the Cl ion has an oxidation number of -1, and in this case there are three of them in the compound. This means that the Al ion must be +3 for the entire compound to be neutral.

This method is very good, since the correctness of the solution can always be checked by adding all the oxidation levels together.

The second method can be used without knowledge of chemical laws:

Find data on particles for which there are no strict rules and the exact number of their electrons is unknown (this can be done by exclusion).
Find out the indicators of all other particles and then find the desired particle from the total by subtraction.

Let's consider the second method using the example of the substance Na2SO4, in which the sulfur atom S is not determined, it is only known that it is different from zero.

To find what all oxidation states are equal to:

Find known elements, keeping in mind traditional rules and exceptions.
Na ion = +1, and each oxygen = -2.
Multiply the number of particles of each substance by their electrons to obtain the oxidation states of all atoms except one.
Na2SO4 contains 2 sodium and 4 oxygen; when multiplied, it turns out: 2 X +1 = 2 is the oxidation number of all sodium particles and 4 X -2 = -8 - oxygen.
Add the results obtained 2+(-8) =-6 - this is the total charge of the compound without the sulfur particle.
Represent the chemical notation as an equation: sum of known data + unknown number = total charge.
Na2SO4 is represented as follows: -6 + S = 0, S = 0 + 6, S = 6.

Thus, to use the second method, it is enough to know the simple laws of arithmetic.

The ability to find the oxidation state of chemical elements is a prerequisite for successfully solving chemical equations that describe redox reactions. Without it, you will not be able to create the exact formula of a substance resulting from a reaction between various chemical elements. As a result, solving chemical problems based on such equations will be either impossible or erroneous.

The concept of oxidation state of a chemical element
Oxidation state is a conventional value with which it is customary to describe redox reactions. Numerically, it is equal to the number of electrons that an atom acquiring a positive charge gives up, or the number of electrons that an atom acquiring a negative charge attaches to itself.

In redox reactions, the concept of oxidation state is used to determine the chemical formulas of compounds of elements resulting from the interaction of several substances.

At first glance, it may seem that the oxidation number is equivalent to the concept of valence of a chemical element, but this is not so. Concept valence used to quantify electronic interactions in covalent compounds, that is, compounds formed by the formation of shared electron pairs. Oxidation number is used to describe reactions that lose or gain electrons.

Unlike valency, which is a neutral characteristic, the oxidation state can have a positive, negative, or zero value. A positive value corresponds to the number of electrons given up, and a negative value to the number of electrons added. A value of zero means that the element is either in its elemental form, has been reduced to 0 after oxidation, or has been oxidized to zero after a previous reduction.

How to determine the oxidation state of a specific chemical element
Determining the oxidation state for a specific chemical element is subject to the following rules:

The oxidation state of simple substances is always zero.
Alkali metals, which are in the first group of the periodic table, have an oxidation state of +1.
Alkaline earth metals, which occupy the second group in the periodic table, have an oxidation state of +2.
Hydrogen in compounds with various non-metals always exhibits an oxidation state of +1, and in compounds with metals +1.
The oxidation state of molecular oxygen in all compounds considered in the school course of inorganic chemistry is -2. Fluorine -1.
When determining the degree of oxidation in the products of chemical reactions, they proceed from the rule of electrical neutrality, according to which the sum of the oxidation states of the various elements that make up the substance must be equal to zero.
Aluminum in all compounds exhibits an oxidation state of +3.

Then, as a rule, difficulties begin, since the remaining chemical elements demonstrate and exhibit a variable degree of oxidation depending on the types of atoms of other substances involved in the compound.

There are higher, lower and intermediate oxidation states. The highest oxidation state, like valency, corresponds to the group number of a chemical element in the periodic table, but has a positive value. The lowest oxidation state is numerically equal to the difference between the number 8 group of the element. An intermediate oxidation state will be any number ranging from the lowest oxidation state to the highest.

To help you navigate the variety of oxidation states of chemical elements, we bring to your attention the following auxiliary table. Select the element you are interested in and you will receive the values of its possible oxidation states. Rarely occurring values will be indicated in parentheses.

To determine the conditional charge of atoms in redox reactions, use the table of oxidation of chemical elements. Depending on the properties of the atom, an element can exhibit a positive or negative oxidation state.

What is oxidation number

The conditional charge of the atoms of elements in complex substances is called the oxidation state. The charge value of atoms is recorded in redox reactions to understand which element is a reducing agent and which is an oxidizing agent.

The oxidation state is related to electronegativity, which shows the ability of atoms to accept or give up electrons. The higher the electronegativity value, the greater the ability of an atom to lose electrons in reactions.

Rice. 1. Electronegativity series.

The oxidation state can have three values:

zero- the atom is at rest (all simple substances have an oxidation state of 0);
positive- the atom gives up electrons and is a reducing agent (all metals, some non-metals);
negative- the atom accepts electrons and is an oxidizing agent (most nonmetals).

For example, the oxidation states in the reaction of sodium with chlorine are as follows:

2Na 0 + Cl 2 0 → 2Na +1 Cl -1

In the reaction of metals with nonmetals, the metal is always the reducing agent and the nonmetal is the oxidizing agent.

How to determine

There is a table that shows all the possible oxidation states of elements.

*Name*	*Symbol*	*Oxidation state*



Beryllium
		1, 0, +1, +2, +3
		4, -3, -2, -1, 0, +2, +4
		3, -2, -1, 0, +1, +2, +3, +4, +5
Oxygen		2, -1, 0, +1, +2




Aluminum



		1, 0, +1, +3, +5, +7, rarely +2 and +4







Manganese		2, +3, +4, +6, +7
		2, +3, rarely +4 and +6
		2, +3, rarely +4
		2, rarely +1, +3, +4
		1, +2, rarely +3

		3, rarely +2
Germanium
		3, +3, +5, rarely +2
		2, +4, +6, rarely +2
		1, +1, +5, rarely +3, +4


Strontium

Zirconium		4, rarely +2, +3
		3, +5, rarely +2, +4
Molybdenum		3, +6, rarely +2, +3, +5
Technetium
		3, +4, +8, rarely +2, +6, +7
		4, rarely +2, +3, +6
Palladium		2, +4, rarely +6
		1, rarely +2, +3
		2, rarely +1
		3, rarely +1, +2

		3, +3, +5, rarely +4
		2, +4, +6, rare
		1, +1, +5, +7, rarely +3, +4





Praseodymium

Promethium
		3, rarely +2
		3, rarely +2
Gadolinium

Dysprosium


		3, rarely +2
Ytterbium		3, rarely +2


		5, rarely +3, +4
Tungsten		6, rarely +2, +3, +4, +5
		2, +4, +6, +7, rarely -1, +1, +3, +5
		3, +4, +6, +8, rarely +2
		3, +4, +6, rarely +1, +2
		2, +4, +6, rarely +1, +3
		1, +3, rarely +2

		1, +3, rarely +2

		3, rarely +3, +2, +4, +5
		2, +4, rarely -2, +6

Or use this version of the table in your lessons.

Rice. 2. Table of oxidation states.

In addition, the oxidation states of chemical elements can be determined from the periodic table of Mendeleev:

the highest degree (maximum positive) coincides with the group number;
to determine the minimum value of the oxidation state, eight is subtracted from the group number.

Rice. 3. Periodic table.

Most nonmetals have positive and negative oxidation states. For example, silicon is in group IV, which means its maximum oxidation state is +4 and minimum -4. In compounds of non-metals (SO 3 , CO 2 , SiC), the oxidizing agent is a non-metal with a negative oxidation state or with a high electronegativity value. For example, in the compound PCl 3, phosphorus has an oxidation state of +3, chlorine -1. The electronegativity of phosphorus is 2.19, chlorine is 3.16.

The second rule does not work for alkali and alkaline earth metals, which always have one positive oxidation state equal to the group number. Exceptions are magnesium and beryllium (+1, +2). Also have a constant oxidation state:

aluminum (+3);
zinc (+2);
cadmium (+2).

The remaining metals have a variable oxidation state. In most reactions they act as a reducing agent. In rare cases, they can be oxidizing agents with a negative oxidation state.

Fluorine is the most powerful oxidizing agent. Its oxidation state is always -1.

What have we learned?

From the 8th grade lesson we learned about the degree of oxidation. This is a conventional value showing how many electrons an atom can give or take during a chemical reaction. The value is related to electronegativity. Oxidizing agents accept electrons and have a negative oxidation state, while reducing agents donate electrons and exhibit a positive oxidation state. Most metals are reducing agents with a constant or variable oxidation state. Nonmetals can exhibit oxidizing and reducing properties depending on the substance with which they react.

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