Advice 1: How to determine the oxidation state in the complex connection

Complex compounds – a chemical substance with a complex structure consisting of a Central atom of the complexing agent, as well as internal and external spheres. The inner sphere consists of neutral molecules or ions, is strongly associated with the complexing agent. Such molecules are called ligands. The external field may consist of anions or cations. In any complex connection elements included in its composition, has its degree of oxidation.
How to determine the oxidation state in the complex connection
Instruction
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Take, for example, a substance formed by the reaction of the gold "Aqua Regia" – a mixture of three parts concentrated hydrochloric acid and one part concentrated nitric acid. The reaction proceeds according to the scheme: Au + 4HCl + HNO3 = H[Au(Cl)4] + NO + 2H2O.
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The result is a complex compound – tetrachloraurate hydrogen. A complexing agent in it is an ion of gold, the ligands – chloride ions, outer sphere is the hydrogen ion. How do you determine the degree of oxidation of the elements in this complex compound?
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First, determine which of the elements composing the molecule, the electronegative, i.e., who will compete for the total electron density. It certainly chlorine, as it is located in the upper right part of the periodic table, and electronegativity is second only to fluorine and oxygen. Therefore, its degree of oxidation will be with the sign "minus". What is the value of the degree of oxidation of the chlorine?
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Chlorine, like all Halogens, is located in the 7th group of the periodic table, its outer electron level is 7 electrons. Dragging on this level is another electron, it will move in a stable position. Thus, its degree of oxidation is -1. And because this complex compound with four chlorine ions, the total charge will be equal to -4.
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But the sum of the degrees of oxidation of the elements composing the molecules must be zero, since any molecule is electrically neutral. Thus, the negative charge of -4 must be balanced by a positive charge of +4 due to hydrogen and gold.
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Since hydrogen is the first element of the periodic table and can contribute to the formation of a chemical bond of only one electron, its degree of oxidation equal to +1. Accordingly, in order to the total charge of molecule is zero, the gold ion must have a degree of oxidation of +3. The problem is solved.

Advice 2: How to arrange the degree of oxidation

Electrons are part of atoms. And complex substances, in turn, of these atoms (atoms form elements) and electrons are divided among themselves. The degree of oxidation shows how many electrons the atom itself took, how much and what is given. This figure can be determined.
How to arrange the degree of oxidation
You will need
  • School textbook on chemistry 8-9, periodic table, table of electronegativity of elements (printed in school textbooks in chemistry).
Instruction
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First we need to indicate that the degree of oxidation - is a relative concept, the host for ion, that is, not deepening into the structure. If the item is in a free state, it is the simplest case formed by a simple substance, and therefore the degree of oxidation equal to zero. For example, hydrogen, oxygen, nitrogen, fluorine, etc.
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In complex substances, things are different: electrons between atoms are not equally distributed, and the degree of oxidation helps to determine the amount given or accepted electrons. The degree of oxidation may be positive and negative. In the advantage of electrons is given, in the red accepted. Some elements of your degree of oxidation retain various compounds, but a this feature is no different. You need to remember an important rule - the sum of the degree of oxidation is always zero. The simplest example of gas: knowing that the degree of oxidation of oxygen in the vast majority of cases equal to -2 and using the above rule, we can calculate the degree of oxidation for carbon C. In the amount of -2 zero gives only +2, and hence the degree of oxidation of carbon +2. Let's complicate the task and we take for the calculations, the CO2 gas that the degree of oxidation of the oxygen remains -2, but the molecules of it, in this case two. Therefore, (-2) * 2 = (-4). The number in the sum gives zero -4, +4, that is, this gas, carbon has a degree of oxidation of +4. A more complex example: H2SO4 - hydrogen degree of oxidation of +1, oxygen -2. In particular compound 2 molecules of hydrogen and 4 of oxygen, i.e. the charges will be, respectively, +2 and -8. In order to sum to zero, you need to add 6 plus. Hence, the degree of oxidation of sulfur is +6.
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When the connection is difficult to determine where plus, where a minus, necessary table of electronegativity (it is easy to find in the textbook in General chemistry). Metals often have a positive degree of oxidation, and the nonmetals negative. But for example, PI3 - both elements are nonmetals. The table shows that the electronegativity of iodine is 2.6, and phosphorus of 2.2. When compared, it turns out that the 2.6 is more than 2.2, that is, the electrons are pulled together in the direction of iodine (iodine has a negative degree of oxidation). Follow these simple examples, you can easily determine the degree of oxidation of any element in the compounds.
Note
Not to be confused with metals and nonmetals, then the oxidation will be easier to find and not confusing.

Advice 3: How to determine the degree of oxidation of a substance

The degree of oxidation , the conditional charge of the atom in the compound, calculated on the assumption that it consists only of ions. Some elements have a constant degree of oxidation, while others are able to change it. In order to identify substances having different connections, different values will use a special algorithm.
How to determine the degree of oxidation of a substance
Instruction
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The degree of oxidation is written above the symbol of the element, the stitch sign is placed, and then the value. It can be negative, positive or equal to zero. The sum of all degrees of oxidation in the substance is equal to zero. Some substances have a constant degree of oxidation for all compounds. For example, in metals it is always positive and equal to their valency (ability to attach or to replace a certain number of atoms or groups of atoms). The alkali metals have a degree of oxidation of +1, while alkaline earth is +2. Hydrogen always has a degree of oxidation of +1, except the hydrides, there is -1 (for example, KH(-1)). The degree of oxidation of the oxygen equal to -2 exceptions: peroxide (BaO2(-1)) and fluoride oxygen(O(+2)F). Fluorine always has -1(DQ(-1)).
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If the substance consists of one or more atoms of the same name, i.e. it is simple, its degree of oxidation equal to zero. For example, H2, Ag, O2, Na, etc.
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Complex substance in the first place set value of the degree of oxidation of the elements, which it is not changed. Then we make an equation with one unknown, i.e. the degree of oxidationthat you need to find, denoted by X. for Solve this equation, we obtain the desired value. It should be noted that in the presence of a complex substance of several atoms of the same element, the degree of oxidation in the preparation of the equations is multiplied by the number of items. Consider the examples.
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If you need to find the degree of oxidation of sulphur in the substance Na2SO4 doing so: first, we arrange the known values are Na(+1)2SO(-2)4. We denote the degree of oxidation of sulfur for X, we write the equation, remembering about the fact that the sum of all the degree of oxidation is always zero: 2+X-8 = 0. Solve: X = 8-2 = +6. Therefore, the degree of oxidation of sulfur is +6.
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Another example: AgNO3. Place: Ag(+1)NO(-2)3. We obtain the equation: 1+X-6 = 0. Calculated: X = 6-1 = +5. The desired value is found.
Note
The degree of oxidation can have fractional values, for example in magnetic iron ore Fe2O3 is +8/3.

Advice 4: How to calculate oxidation number

Oxidation is common in textbooks of chemistry characteristics of elements. There are a large number of tasks aimed at the definition of this extent, and many of them cause students difficulties. But, following a specific algorithm, these difficulties can be avoided.
How to calculate oxidation number
You will need
  • - the periodic system of chemical elements (Mendeleev's table).
Instruction
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Remember one General rule: the oxidation number of any element in a simple substance is equal to zero (examples of elements: Na, Mg, Al, i.e. substances composed of atoms of one element). To determine the degree of oxidation of the complex substances in the beginning just write it down without losing the indexes, digits, standing at the bottom right next to the element symbol. An example would be sulfuric acid — H2SO4.
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Next, open the table of D. I. Mendeleev find the oxidation state of the leftmost element in the substance — hydrogen in the case of this example. Under the current rules, its oxidation number will always be positive, and it is written with the sign "+", as it occupies the leftmost position in the record formula of a substance. To determine the numeric value of the degree of oxidation, note the location of the item relative to groups. Hydrogen is in the first group, therefore, its degree of oxidation +1, but since sulfuric acid two hydrogen atoms (this shows us the index), then write the symbol +2.
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Then determine the oxidation state of the rightmost element in the recording — oxygen in this case. His conditional charge (or oxidation state) is always negative, as it occupies the right position in the recording substance. This rule holds true in all cases. The numerical value of the right element is the subtraction from the number of his group of 8. In this case, the oxidation state of oxygen is -2 (6-8=-2), given the index is -8.
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To find the conditional charge of the atom of a third element, use the rule — sum of oxidation States of all elements must equal zero. Then, the conditional charge of the oxygen atom in a substance is equal to +6: (+2)+(+6)+(-8)=0. After this, write +6 over the symbol for sulfur.
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