Why is there a valence change in the valence and how does the valence change

This question is a good question, there is no valence problem of compounds, it is the elements that are valorized. Whereas, elemental valence is caused by a change in the number of electrons in the outer shell of a molecule or ion. The molecules of each element have a fixed electronic arrangement, according to the first shell 2, the second shell 8, the third shell 8 and so arranged, and then the later ones are more complex, there will be sublayers and so on.

Many elemental molecules are not stable, taking the elements of the 2 electron shell as an example, if the outermost electron is greater than 4, it needs to seize the electron to become a stable structure of 8 electrons, and if it is less than 4, it is easy to lose the outer electron and become a stable structure, so that the number of electrons changes, and the macroscopic performance is valence. Because of this, most of the elements in their natural form, except for the inert ones, are in the form of compounds. When metals are combined with non-metals, because the outer electrons of the metal are unstable, the electrons are completely taken away to form ions, which can be completely separated independently in the aqueous solution.

The combination of non-metallic elements, molecules generally do not have the ability to completely seize each other's electrons, and can only form shared electron pairs between molecules, such as CO2, HCl, in this case, the electron pairs will be close to the side with strong binding force to the electrons, and the element will show negative valence because the electrons are close, and the other side will show negative valence. For example, non-metallic elements such as oxygen also share electron pairs between molecules, and because the molecular capacity is the same, the electron pairs are centered, and the valency of the element is 0.

The valency of the same element will also be different in different compounds, such as iron, which is due to the electron subshell, and C and other elements. Generally speaking, each element has only one of the most stable valence states when forming compounds, and the other valence states are unstable, and the unstable valence states have strong oxidation or reduction, and if they encounter oxidants or reducing agents, they are easy to change their valence and transform into a stable valence state.

Valence is due to the electronic configuration, and the valence is different in different situations. For example, why does iron have a +2, +3 price:

First, when the outermost shell is saturated or semi-saturated with electron numbers, the atomic energy is stable as ions (or shared electron pairs). The electron row of iron is 2,8,14,2, so the outermost shell can lose 2 electrons in +2 valence. When the outermost shell does not lose, while the subouter shell loses 3 electrons, the subshell 3d is semi-saturated with all +3 valence.

When different elements are combined, the outermost electron shell generally tends to stabilize the number of electrons, such as 8 electrons. The product can be stable. And there are many ways for the outermost shell to reach 8 electrons, so there are many valencies.

However, it is not a random number of valences, and there are generally several fixed ones.

Because his outermost electron is stable if it is 8 or 4.

Because different elements have different electron shell arrangements.

The outermost electron is determined by the amount of gain and loss.

A chemical reaction in which there is a change in the valency of an element during the reaction is called a redox reaction. This reaction can be understood as consisting of two halves, namely oxidation and reduction. The essence of the reaction is that there is a transfer (or shift of electrons) in electrons, which is characterized by the rise and fall of valency.

The half-reaction in which the valency increases, i.e., the electron loss is an oxidation reaction; The reaction in which the valency decreases and the electrons are obtained is a reduction reaction. Substances with increased valence reduce each other and are oxidized by themselves, so they are called reducing agents, and their products are called oxidation products; Substances with reduced valency oxidize each other and are reduced themselves, so they are called oxidants, and their products are called reducing products. Namely:

Reducer. Oxidant.

Oxidation products. Generally speaking, the reducing product in the same reaction is weaker than the reducing agent, and the oxidation of the oxidation product is weaker than that of the oxidant, which is the so-called "strong reducing agent to weak reducing agent, strong oxidant to weak oxidant". Summary:

The oxidant undergoes a reduction reaction, electrons are obtained, the valency is reduced, it is oxidized, it is reduced, and the reduction product is generated. The reducing agent undergoes an oxidation reaction, loses electrons, increases the valency, has reducibility, is oxidized, and generates oxidation products. Notation:

Redox is inseparable, and the gain and loss of electrons is fundamental. Those who lose electrons are oxidized, and those who gain electrons are reduced. Reducing agent for those who lose electrons, oxidizing agent for those who gain electrons.

Oxidant. Reducing agents, interdependent and inseparable. Notation 2: Ascend and lose oxygen and return oxygen, and drop and return oxygen to explain:

1.The valency increases, electrons are lost, an oxidation reaction occurs, and it acts as a reducing agent, and the product has less oxidation than the oxidant in the reactant. 2.

The valency decreases, electrons are obtained, a reduction reaction occurs, and acts as an oxidant, and the product has a weaker reducing property than the reducing agent in the reactant. Notation 3: Rise and loss are returned to oxygen and oxygen is returned to oxygen Explanation:

1.The valency increases, electrons are lost, and they are oxidized as reducing agents. 2.

The valency decreases, electrons are obtained, and they are reduced to oxidants. Notation 4: Peel off the camouflage coat (lose electrons), the real face is reduced is the reducing agent, the reducing agent of course oxidation reaction, the electron is negative valence, the loss of electrons is negative, the valency is increased and put on the camouflage coat (to get electrons), the real face is oxidized is the oxidant, the oxidant of course undergoes a reduction reaction, the electrons are negative valence, the electrons are positive and negative, and the valency is reduced.

It is the valence change of a substance when a redox reaction occurs.

1.The following are two small poems about valence

Regular-priced song. N-monohydrogen, potassium, sodium, ammonia, silver, n-dicalcium, magnesium, barium and zinc, copper-one-two, iron-two-three, trialuminum, tetrasilicon, two-tetracarbon.

Negative price song. Negative monohydroxide, nitrate, fluorochlorobromide, minus disulfite, carbonate, oxygen and sulfur, negative triazine valence, chloride, phosphorus, sulfur, manganese and carbon, roots and non-metals are mostly seen in negative valence.

Chlorine, manganese, sulfur, nitrogen, phosphorus, all of these elements.

Three or four valencies can be recorded separately. Also note that the valency of all elements in the element is 0The rest is based on the above two poems. The two poems were taught to us by my junior high school chemistry teacher, and I personally feel that they are particularly useful, especially the "regular price song".

Compound reaction is a very important type of reaction in chemistry, in which the change in valency is one of its most basic characteristics.

Valency refers to the atomic value of an element in a compound, usually expressed in Arabic numerals, such as hydrogen has a valency of +1 and oxygen has a valency of -2. In a chemical reaction, atoms form compounds by sharing or transferring electrons, so the valency also changes.

For example, when hydrogen and oxygen undergo a fusion reaction to form water, the hydrogen atom loses one electron and the oxygen atom gains two electrons, so the valency of hydrogen changes from +1 to 0, and the valency of oxygen changes from 0 to -2. The reaction formula can be expressed as: 2H2 + O2 2H2O.

However, in some chemical reactions, the valency does not change, and in this case the compound is still stable. This is because the way in which electrons are shared between atoms keeps their valency constant.

For example, when oxygen and nitrogen react to form nitrous oxide, the valency of oxygen is still -2 and the valency of nitrogen is still -3. The reaction formula can be expressed as: N2 + 2O2 2NO2.

The change in valency is closely related to the change in the energy of the chemical reaction. In some chemical reactions, the change in valency is accompanied by the release or absorption of energy. This change in energy can be used to fuel a chemical reaction or to store energy.

In conclusion, the change in valency in a chemical reaction is one of the basic characteristics of a chemical reaction, but not all of the reaction is accompanied by a change in valency. This change is closely related to the energy change of the reaction, which is of great significance for the research and application of chemical reactions.

1) h: valency from 0 to +1, o: valency from 0 to -2, oxidant:

O2, Reducing Agent: H2, Oxidation Product: H2O, Reducing Product:

h2o。(2) p: valency changes from 0 to +5, o:

The valency changes from 0 to -2, oxidant: O2, reducing agent: p, oxidation product:

P2O5, reduction product: P2O5. （3）cl：

The valency changes from +5 to -1, O: the valency changes from -2 to 0, oxidant: kclo3, reducing agent:

KCLO3, oxidation product: O2, reduction product: KCL.

4) Hg: valency from +2 to 0, O: valency from -2 to 0, oxidant:

HGO, reducing agent: HGO, oxidation product: O2, reducing product:

hg。(5) w: valency changes from +6 to 0, h:

The valency changes from 0 to +1, oxidant: wo3, reducing agent: H2, oxidation product:

H2O, reduction product: W.

1. The change of valency is the reaction of gaining and losing electrons;

2. When the redox reaction occurs, there will be valency changes;

3. If a non-redox reaction occurs, the valency does not change;

4. The reaction with valency change is called redox reaction;

5. The valency does not change and is called a non-redox reaction;

6. Potassium hydrogen, sodium silver, calcium, zinc, magnesium, barium, negative monovalent hydroxide nitrate, negative two annihilation argument valence sulfate carbonate, and ammonium root in the positive price of the banquet to change the source price.

The change in valency is multiplied by the foot code of the changing element and then multiplied by the number of measurements in front of the chemical formula.

For example, 2H2O2 = (MNO2 catalyst) = 2H2O+O2 Calculate the number of electrons transferred, you can calculate the transfer of elements with increased valency, and you can also calculate the transfer of elements with reduced valency.

In this reaction, part of the oxygen element -1 becomes -2, and part -1 becomes 0, and the number of electrons transferred is.

Varying valency = 1

Foot code = 2 The number of meters in front of the chemical formula = 2

Number of electrons transferred = 2 2 1 = 4

The increase and decrease are divided into half, so the final number of electrons transferred is 4