Which reactions have valency changes in junior high chemistry

A change in valency is the occurrence of a redox reaction. Therefore, in junior high school chemistry, the reactions that change the valency are: displacement reaction, combustion reaction, some chemical reactions (C and O2 reaction to form CO2) and decomposition reaction (electrolysis of water to form H2 and O2).

But the metathesis reaction is definitely not! The formation of H2CO3 by H2O and CO2 is also a chemical reaction, but no change in valency occurs in this reaction.

Valency before and after junior high school chemical reactions.

The changes are: 1. Displacement reaction.

Zn + 2HCl = ZnCl2 + H2 2, chemical reaction with elemental participation; For example: 2cu + o2= = 2cuO3, there is a decomposition reaction of elemental generation; For example: 2H2O energized 2H2 + O2 4, combustion reaction; For example:

CH4 + 2O2 = ignition = CO2 + 2H2O

5. Redox reaction between metal oxides and CO.

For example: co+ cuo = = cu + co2

It's hard to generalize, you can do the math yourself, and the valence state of each reactant and product will be clear.

The valency of some elements is generally unchanged when labeling, such as oxygen (when a compound becomes a compound), which is ...... by common sense

Valence: One price please donkey feet take silver, (monovalent hydrochloride potassium sodium silver) bivalent sheep Gaimei vest. (divalent oxygen, calcium, magnesium, barium, zinc).

monovalent potassium, sodium, potassium, potassium, potassium, magnesium, zinc;

trialuminum, tetrasilicon, pentavalent phosphorus, ditrifer, ditetracarbon;

Nitrogen is found in the first to fifth valents, with copper mercury bivalent being the most common.

positive copper, potassium, potassium, sodium, silver, copper, magnesium, calcium, barium, zinc;

trialuminum, tetrasilicon, tetrahexasulfur, 245, nitrogen, 35 phosphorus;

157 chlorodiferric, 2467 manganese is positive;

Carbon has positive four and positive two, and then keep the negative price in mind;

Negative iodine bromo, fluorochlorine, negative dioxysulfur, phosphorus triazonide.

Common atomic group valence decision in junior high school:

Negative hydroxide nitrate, negative disulfite carbonate, and negative triphosphate, only ammonium is positive one.

hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon;

Sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chloride, argon, potassium, calcium.

To remember the valency, we often use the following formula:

Monovalent potassium hydrochloride, sodium silver, bivalent calcium, magnesium, barium oxygen, zinc.

Two copper, three aluminum, four seven manganese, two four hexasulfur, two four carbon, three valent nitrogen and phosphorus, iron have two or three to remember.

The order of metal activity can be memorized according to the following formula:

Potassium, calcium, sodium, magnesium, aluminum, zinc, iron, tin, lead, hydrogen, copper, mercury, silver, platinum.

There are four major types of chemical reactions in junior high school, of which three have changed valence.

Chemical reaction, decomposition reaction, displacement reaction.

Chemical reactions are mostly reactions of substances with oxygen.

There are very few decomposition reactions, and only electrolyzed water is the valency change.

The displacement reaction is divided into the reaction of metal and acid, and the reaction of metal and salt.

The change in valency is generally a reaction with elemental formation or elemental involvement, because elemental elements are zero-valent.

Just write down the common valencies of common elements, as well as a table of metal activity sequences.

These equations will be fine.

Valency indicates the number of electrons gained and lost by atoms when they are combined with each other, and is a property exhibited by an element when it forms a compound. The valence of valence is generally equal to the number of electrons gained and lost by each atom during compounding, that is, the number of electrons gained and lost when the element can reach a stable structure, which is often determined by the electronic configuration of the element, mainly the outermost electronic configuration.

When elements are combined with each other, the ratio of the number of reactant atoms is not fixed, but is determined by the number of electrons in the outermost shell of the atom. For example, a sodium ion (valency of +1, loss of an electron) must be combined with a chloride ion (valency of -1, gain an electron). And one magnesium ion (valency of +2, loss of two electrons) must be combined with two chloride ions.

If the valency algebraic sum of the ions of the formed compound is not zero, the cations and cations that make up the ionic compound and the outermost electron shell of the atoms that make up the molecule of the covalent compound cannot be made a stable structure. It is not possible to form stable compounds.

The concept of valency comes from this, then the number of electrons outside the nucleus of an element that are mutually combined determines the valency of this element, and the valency is set to conveniently represent the number of atoms that are mutually combined. When learning valency, you should be aware of the rules for elemental valency in compounds.

In addition, it is stipulated that the valency of an element is zero, and the algebraic sum of the valency of the positive and negative ions of the constituent positive and negative ions is zero, regardless of ionic compound or covalent compound. Ionic compounds, e.g., NaOH (sodium valency is positive 1 valence, hydroxide ion valency is negative 1 valence, and the mutual cancellation is zero valence).

Valency – the ability of an atom to form a chemical bond. are the chemical properties of the elements that form a stable compound in each other. (i.e., the ability to achieve a stable structure of the elements).

Note: The "valency" of an element is an important property of the element, which is only manifested when it is combined with other elements. That is to say, when the element exists in a free state, that is, when it does not combine with other elements to form a compound, the valency of the elemental element is "0".

For example, metal elements such as iron, non-metallic elements such as carbon, and rare gases such as helium.

It refers to a chemical reaction in which two or more substances produce a new substance. (Tremor can be recorded as "multi-changeable one" when remembering) valency change h2 + o2 = ignition = 2h2o decomposition reaction is one of the common types of chemical reactions, and it is the reverse reaction of chemical reactions. It refers to the decomposition of a compound into two or more simple elements or compounds under specific conditions (such as heating, direct current, catalyst, etc.), which is called decomposition reaction, valency change 2H2O = energized = 2H2 + O2 Replacement reaction is one of the basic types of inorganic chemical reactions, refers to the reaction of one element and one compound to generate another element and another compound, which can be expressed as:

Valency changes.

A+BC B+AC Fe+CuSO4=FeSO4+CU displacement relationship refers to the substitution of an element that makes up a compound by an element that makes up a element. The mu-closure reaction in which two compounds exchange components with each other to produce two other compounds is called metathesis reaction. Its essence is:

The two substances that undergo metathesis reaction exchange ions with each other in the aqueous solution, and combine into substances that are difficult to ionize--- precipitation, gas, and water, so that the ion concentration in the solution decreases, and the chemical reaction proceeds in the direction of the decrease in ion concentration. The valence must remain the same.

It can be abbreviated as ab cd = ad cb h2so4 + 2naoh = na2so4 + 2h2o

Compound antibeam dust should be variable one 2H2 + O2 ignition = 2H2O may change quietly or unchanged Decomposition reaction One becomes more 2H2O energized = 2H2 +O2 may or may not change Displacement reaction Elemental and compound reaction to form another elemental compound Fe+CuSO4=Feso4+Cu Definite metathesis reaction The two compounds are exchanged into acorns, and the reaction of the other two compounds is claimed HCl+NaOH=NaCl+H2O, which must be inconvenient, thank you.

CaO+H20=Ca[OH]2 The valence of CaCO3=CaO+CO2 remains unchanged, the valency of Mg+ZnCl2=MgCl2+Zn Mg will increase, and the valency of Na2CO3 +CaCl2=CaCO3+2NaCl will remain unchanged.

You can understand this way.

If it has "sub", it means that the valency of this element is not the most **, but the intermediate valence, such as ferrous sulfate, and iron is +2 valence.

Sulfurous acid, sulfur is +2 valence.

In cuprous sulfate, copper is +2 valence.

If it has "high", it means that the valency of this element is the most **, such as perchloric acid, which has a chlorine of +7 valence.

In fact, there are not many such examples in junior high school chemistry.

The regularity is also not strong.

So when you meet one, it's okay to remember one.

HCO4 perchlorate, chlorine is +7 valence.

HCO3 chloric acid, chlorine is +5 valence.

Chlorite HCO2, chlorine is +3 valence.

Hypochlorite HCLO, chlorine is +1 valence.

over~~

Ferrous sulphate is FeSo4 and ferric sulphate is (Fe)2(SO4)3. Ferrous ions are +2 valence, while iron ions are +3 valence, +1 valence copper is not common in junior high school, and it is not required to master, potassium permanganate, perchloric acid, etc., indicate that some of these substances have the highest valency of ions, for example, the manganese ion in potassium permanganate is +7 valence, and the chloride ion in perchloric acid is +7 valence. Hope it helps.

Copper usually shows a +2 price, and cuprous is +1 price.

Iron is usually +3 valence, ferrous iron is +2.

Asia is lower than the normal valence, and high is higher than the normal valence.

This needs to be judged according to the periodic table