Knowledge of valency and chemical formula

Memorize the periodic table! ~

Each cycle and each family have their characteristics. According to the family, their outer electrons are the same, and the way of losing or gaining electrons is also similar (forming a valence state), for example, alkali metals are +1, alkaline earths are more +2, halogens are -1 valence, oxygen groups are generally -2....It's good to remember the characteristics and the special oxygen group oxygen is multi-2 valence, but sulfur has any valence state, so you should pay more attention to sulfur and phosphorus are all polyvalent, and you should also look at superoxide ions when encountering them

The chemical formula is a compound composed of different valence elements, and its apparent valence state is zero, so that if you know the common valence states of some common elements, you can know the valence states of those elements that are not commonly used

Chemistry is a mess, and you still need to memorize it by rote, but with a solid foundation, everything is fine!

As a science, it is the study of death before life. It means to learn to die first and then learn to live, learning to die is that first of all, you have to remember the formulas you have learned (it is best to push them yourself to see how the formulas evolved) and other laws, and these are followed by examples from the teacher or books, just like a new knife is first taken to open the seal, and then on this basis, you have to practice, practice more and do more questions, so that your formula can be used in practice, practice makes perfect, and you can remember the natural formula when you are proficient. Then increase the difficulty to do exercises at different levels, there are only a few knowledge points, he mainly wears a few more layers of camouflage, layer by layer to uncover it suddenly realized, the so-called problem is composed of several simple questions, each simple question is a knowledge point, so usually people say that a difficult problem test a few knowledge points is like this...

There are only a few knowledge points, learning science is to practice more, and learning science is fun and promising, when you complete a difficult problem and everyone has not completed it or just a few masters have made it, do you have a sense of achievement?

Inorganic chemistry is mainly about understanding the properties of each element and understanding the principles and processes of chemical reactions.

You can start with the periodic table to find out the common properties of each family, and then remember the characteristics of each element in each family. That's enough.

As for organic chemistry, it is almost as good as understanding the properties and structure of each group, as well as the principle of reaction between different groups.

I memorized all the textbooks back then!

High School Entrance Examination Introduction] Because of persistence, there will be such a beautiful story as breaking the cocoon into a butterfly. As test preparers, we also want to strive for a perfect ending for ourselves. To this end, we have prepared the basic knowledge of chemistry for the high school entrance examination "Basic Concepts of Chemical Formula and Valence", please take a look!

The basic concept of chemical formula and compound hood or precursor.

1) Significance of the chemical formula: Macro significance: adenotes a substance; b.indicates the elemental composition of the substance;

Micro Significance: arepresents a molecule of the substance; b.indicates the molecular composition of the substance; Meaning of quantity: aRepresents the ratio of the number of atoms in a molecule of a substance; b.Indicates the mass ratio of the elements that make up the substance.

2) Reading and writing of elemental chemical formulas.

Directly represented by the element symbol: aElemental metals. Such as: potassium K copper Cu silver AG, etc.;

b.Solid non-metallic. Such as: carbon, C, sulfur, S, phosphorus, P, etc.

c.Noble gas. Such as: helium (gas) HE neon (gas) NE argon (gas) AR and so on.

Polyatoms make up the elemental nature of a molecule: its molecule is made up of several groups of the same kind of atoms, which are written in the lower right corner of the element symbol.

For example, if each oxygen molecule is composed of 2 oxygen atoms, then the chemical formula of oxygen is O2

Diatomic molecule elemental chemical formula: O2 (oxygen), N2 (nitrogen), H2 (hydrogen).

Polyatomic molecule elemental chemical formula: ozone O3, etc.

3) Reading and writing of chemical formulas of compounds: read first and then write, and read first when written.

A compound composed of two elements: read"Some-and-so", such as: MGO (magnesium oxide), NaCl (sodium chloride).

Compound composed of acid radicals and metallic elements: read"A certain acid", such as: KMNO4 (potassium permanganate), K2MNO4 (potassium manganate).

MgSO4 (magnesium sulfate), CaCO3 (calcium carbonate).

4) Judge the valency of the element according to the chemical formula, and write the chemical formula of the compound according to the valency of the element:

The basis for judging the valency of an element is: the algebraic sum of positive and negative valency in the compound is zero.

Steps to write a chemical formula based on the valency of an element:

a.Write out the element symbol according to the element valence, positive, left, negative and right, and mark the valence;

b.See if the valence of the element has a divisibility and is reduced to the simplest ratio;

c.Cross-inversion writes the valency that has been reduced to the simplest ratio in the lower right corner of the element symbol.

For example, the common valency of Cl (chlorine) is -1 valence, but in Clo2 (chlorine dioxide), since the algebraic sum of the valency is zero and oxygen is -2 valence, the valency of Cl + (-2 times 2) = 0 is Cl here. To put it bluntly, the valency of a substance in the chemical formula = 0 - (the valency of another substance multiplied by the number of atoms or ions of the substance).

Valency is when the elements are combined with each other, and the ratio of the number of reactant atoms is always constant. And since atoms are the smallest particles that cannot be separated in a chemical reaction, when the elements are combined with each other to form a certain compound, there must be a certain simple integer ratio between the number of electrons outside the nucleus that changes between the elements.

Chemical formula: The formula that uses element symbols and numbers to represent the composition of matter is called a chemical formula.

Pure substances all have a certain composition, and their composition can be expressed by a corresponding chemical formula. Some chemical formulas can also indicate the molecular composition of the substance, which is also called a molecular formula.

Valency, that is, the property of a certain number of atoms of an element and a certain number of other elements, is called the valency of an element. It is an important property of the element.

Calculation according to the valence should be observed"The sum of the valencies of the elements is equal to zero".For example, in BaCl2, the valency of Ba is +2 valence, and Cl is generally -1 in the compound

valence, according to the addition of valence equal to zero, the formula can be listed: 2*1+(-1x)=0.Find x=2(Note: You can calculate directly orally when you usually calculate, so you don't have to be so troublesome).

Remember: the valency of a single element is zero.

Writing the correct chemical formula is also calculated according to the valence, but the reverse calculation is just the opposite, and the same is observed"The sum of the valencies of the elements is equal to zero".

Valence formula.

Hydrogen +1, Oxygen-2, Silver, Lithium, Sodium, Potassium +L, Zinc, Magnesium, Calcium, Barium +2, Aluminum +3, Silicon +4

Only metal or hydrogen, nitrogen, phosphorus-3, sulfur-2, chlorochlorobromide-iodine total -1

Variable price, not terrible, specific judgment"and zero".

If the element is zero, it should be remembered.

A chemical formula is a formula that uses element symbols to represent the composition of matter, and the sum of the relative atomic masses of each atom in the chemical formula is the quantity of the formula.

This was given to us by our teacher at that time.

Valency is still very useful, and it is good for doing problems after memorizing it. In fact, chemistry is still a very good subject, don't blame chemistry).

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

Trialuminum, tetrasilicon, pentavalent phosphorus, di-triiron, ditetracarbon.

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

Hydrogen, lithium, sodium, potassium, ammonia, beryllium, magnesium, calcium, barium, boron, aluminum, iron.

Carbon-silicon-tin-lead bi.

Fourth, nitrogen and phosphorus phosphate.

Dithosulfate trioxysulfate.

Chlorochlorobromoiodine.