Find out how the valence of chemistry is marked and how it changes together in junior high and high

Give you a mantra that a teacher taught us Very well memorized.

Potassium, sodium, hydrogen, silver +1 valence.

Calcium, magnesium, barium, zinc +2 valence.

CFO-iodine-1 valence.

Copper, iron, aluminum+3, silicon+4

Usually oxygen is -2 valent.

Valency of atomic clusters:

1 Nitric acid, hydroxide.

2 Sulfuric acid, carbonate.

Only +1 is ammonium.

It's really useful.

Well, actually, valency starts with the structure of atoms and ions.

For example, oxygen is element number 8 of the periodic table, then its atomic structure diagram is (+8)2 6

The outermost shell is 6 electrons, so it's easy to get 2 electrons in a chemical reaction, and you can take two units of negative charge to form ions, so it's -2 valence.

Of course, the valency of the same element may change in different substances This point should be paid attention to, it is really not possible to buy the book of the first semester of the third semester of the junior high school of the teaching version of the book I am learning now If you don't know the topic, you can also come and say hello directly! Sister, I'm happy to answer

First, it is necessary to understand the valency of the elements in the compound, such as H2O, H+1 valence, and O-2 valence;

Write +1 or -2 and so on directly above the symbol of the second element.

h2o the rest is the same.

It's valency, right? The valence table is in the upper right corner of the element symbol, and the electrons are in the negative sign in the upper right corner, and the electrons are positive, and the corresponding number must be added in front of the symbol to get a few or go to a few, such as hydrogen ions are h-, because the computer is not good to mark, remember that ha, the symbol is in the upper right corner, not the right oh, the upper right corner, na+, s2-, o2-, these.

Valence formula.

The main valency of common elements.

chlorochlorobromoiodine negative monovalent; N-monohydrogen silver with potassium sodium.

The minus two of oxygen should be remembered first; n-dimagnesium, calcium, barium and zinc.

positive three is aluminum, positive four silicon; Let's put the price change down.

All metals are regular; One or two coppers come two or three irons.

Manganese is 24 and 67; The two or four of carbon should be kept in mind.

non-metallic negative main is uneven; Chlorine is negative one positive one five seven.

Nitrogen and phosphorus minus three and plus five; Different phosphorus, three nitrogen, two or four.

Sulfur has minus two, positive, four-six; It will be cooked when you use it while memorizing it.

Common root price formulas:

monovalent ammonium nitrate; Hydrohalide hydroxide.

permanganate chlorate; Perchlorate acetate.

divalent carbonate sulfate; Manganese hydrosulfate.

Suspense ammonium is the normal price; Negative three has a phosphate group.

Methods of marking valence:

1.In compounds, the valency of the element is specified based on the algebra of positive and negative valency and the calculation of zero.

2.The valence of the element is clearly marked directly above the element, and the plus and minus signs are always marked.

3.When the aerobic element is present, the oxygen element is written on the back.

4.The elemental symbol of metallic matter is written in the front, and the elemental symbol of non-metallic substance is written in the back.

Extended Information: Determining the valency of elements in a compound, note:

1) There are positive and negative valences.

2) Oxygen is usually -2 valence.

3) Hydrogen usually shows +1 valence.

4) When metallic elements and non-metallic elements are combined, metallic elements show positive valence, and non-metallic elements show negative valence (generally speaking, the positive valence is written in the front, and the negative valence is written in the back).

5) Some elements can show different valencies in the same substance.

6) The algebraic sum of positive and negative valencies in a compound is 0.

7) The valency of an element is a property exhibited by the atoms of an element when forming a compound, so in a elemental molecule, the valency of an element is 0.

According to the valency, write the chemical formula: The cross method is used to write the chemical formula according to the valency, before the metal, after the non-metal, and after the oxygen in the oxide. For example:

How to write the chemical formula of alumina: , before the metal, after the non-metal, and after the oxygen in the oxide, write: al o; Mark the valency directly above the element symbol, and write 2 in the lower right corner of al and 3 in the lower right corner of o

Alo can be extracted to obtain the chemical formula as: Al2O3; Check the correctness or falsehood of the chemical formula according to the "algebraic sum of the positive and negative valencies of each element in the chemical formula is zero": (+3) 2+( 2) 3 0.

Such a correct chemical formula is written in the criss-cross method.

In junior high school chemistry, the criss-cross method is used to write chemical formulas such as the chemical formulas of substances formed by the combination of aluminum and oxygen according to valency.

1. Write the element symbols in the order of positive elements before negative valence elements.

2. Write the valence cross directly above the element symbol, write 2 in the lower right corner of al, and write 3 in the lower right corner of o.

3-2alo

The chemical formula can be done, ie.

AL2O33, check the correctness or falsehood of the chemical formula according to the algebraic sum of the positive and negative valencies of each element in the chemical formula is zero.

A correct chemical formula is written by the cross method, but when writing the chemical formula by the cross method, it is necessary to pay attention to ensure that the valence of the two elements is a prime number of each other.

3. If the valency of two elements is not a prime number, for example, the chemical formula of the oxide of sulfur with +6 valence.

After marking the valency above the element symbol, take the absolute value and divide it to get 3:1, and write it in the lower right corner of the element symbol to get SO3

How to write the chemical formula of alumina: , before the metal, after the non-metal, and after the oxygen in the oxide, write: al o; Mark the valency directly above the element symbol, and write 2 in the lower right corner of al and 3 in the lower right corner of o

Alo can be extracted to obtain the chemical formula as: Al2O3; Check the correctness or falsehood of the chemical formula according to the "algebraic sum of the positive and negative valencies of each element in the chemical formula is zero": (+3) 2+( 2) 3 0.

Such a correct chemical formula is written in the criss-cross method.

The chemical formula is: Al2O3; Check the correctness or falsehood of the chemical formula according to the "algebraic sum of the positive and negative valencies of each element in the chemical formula is zero": (+3) 2+( 2) 3 0.

Such a correct chemical formula is written in the criss-cross method.

Start by addressing the question of why you want to put parentheses.

When you first learn chemistry, you need to be exposed to chemical terms. First of all, there is the chemical element symbol h o c n fe cu al and the like, and then you will come into contact with the chemical formula. to describe in chemical language, write the names of these substances.

The above symbols are both elemental symbols and atomic symbols, and you can imagine them as the names of these atoms.

So atoms can form clusters of atoms, which are things that atoms come together to form -- and you can imagine thinking of a cluster of atoms as an atom.

Well, with this knowledge, you will be able to understand. Think with common sense.

Several atoms combine to form molecules. We write the molecular formula and use parentheses in order not to cause misunderstandings and troubles.

For example, if we write na0h without parentheses, we will write na0h without parentheses, because a na is accompanied by an oh. And do not write corner mark 1. But ca(oh)2 because ca has two ohs (it doesn't matter why).

If the parentheses are removed, caoh2 will cause misunderstanding.

A few atoms, with a few atoms, are marked in the bottom right corner. As for the specific ratio, it depends on the valence. Make the algebraic sum of valency zero.

And I guess there's going to be basic copper carbonate in those 63 chemical formulas. You can understand it.

Cu2(OH)2 CO3 Cu stands for Copper atom It is not an atomic group without parentheses, but it is necessary to add a corner mark 2 (OH-) is an atomic group and the number is 2, so add parentheses CO3 2- (3) is a cluster of carbonate atoms, but the number is 1, without parentheses. As for why you have to ask why the chemical formula is this. But it's just a matter of being able to tell that it's right.

The valency of Cu is +2 and there are two that are 2*(+2)=+4

The valency of oh- is -1 and there are two that are 2*(-1)=-2

The valency of CO3 2- is -2 and has a 1*(-2)=-2

Algebraic sum to 0 That's it. The same goes for everything else.

If you ask how the valency of an atomic cluster is determined, for example, oh- o is -2 h is +1 natural and is -1

no3 - n is +5 o is -2 *3 = -6 and is -1

CO3 2- c is +4 o is -2 *3 = -6 and is -2

As for what you're told about, the product of valency and the number of molecules, it's actually the number of atoms or the number of clusters of atoms, which is what I did above.

In junior high school, all molecules are electrically neutral, that is, if you touch them, they will not be electrocuted, which explains why algebraic sums are zero. For example, water H2O.

Finally, I want to say that the corner mark in the lower right corner represents the particles in a molecule (particles are atomic clusters of ions......Count, in layman's terms. It's not too hard.

There will usually be an element that has only one valence. Based on this element, the number of other elements is determined, and the chemical formula is written.

Are you talking about 3 or more than 3? 3 kinds are relatively easy to say. Variable price?

How much has it changed? Generally, only one of the three elements is variable, and the specific problem is analyzed, you see that the elements in nitric acid cannot be zero price, right? There is only n to change, and the composition may also be nitrous acid, and there is not only one, but if you take the test, it will not be said that only one is right.

The valence is determined according to the number of electrons outside the nucleus, and the valence is determined according to the activity when the element has a variable valence.

The sum of positive and negative valency is 0, so find the least common multiple of the valency number, and then find a way to match the positive charge with the least common multiple and the negative charge with the least common multiple!

Have you learned to write chemical formulas according to valency.