Who can tell me about the chemical formula and valency of chemistry in junior high school?

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

Na(OH) (the valency of sodium is positive 1 valence, the valency of hydroxide ions is negative 1 valence, and the compound that cancels each other out as zero valent is true).

To memorize the valence state of the mature valence, just remember the algebraic sum as zero. For example: Fe2O3 The valence state of oxygen is negative bivalent (specified) There are three oxygen atoms, that is, 3*2=-6 According to the algebraic sum of zero, 2*()6=0 can be calculated to be the obvious +3 valence of iron.

The valence state of some elements is not certain, and it must be calculated through a certain valence state.

This is the foundation of learning chemistry well, you must learn it well!

Valency is equivalent to the gain and loss of electrons of an atom.

The sum of the total gains and losses of electrons is 0

Mouth trembling and anti-slag formula: common elements are mainly valence formulas.

Monovalent potassium, sodium, silver chloride, divalent magnesium oxygen, calcium, barium, zinc, (sheep do not cover vests), trialuminum, tetrasilicon, pentavalent phosphorus, di-triiron, ditetracarbon, 246 sulfur are all available, and copper and mercury are the most common.

The price element of the eggplant is not terrible, and it is calculated after death and then life.

Common atomic cluster valencies (10 in total).

Positive monovalent: ammonium (NH4+).

Negative monovalent: hydroxide (OH-), nitrate (NO3-), chlorate (CLO3-), permanganate (MNO4-) negative bivalent: carbonate (CO32-), sulfate (SO42-), sulfite (SO32-), manganese acid root (MNO42-) negative trivalent:

Phosphate (PO43-).

The law of valence related:

1. The unit quality is 0 price. Such as O2, H2, S, FE, C, Cu, etc.

2. H is generally +1 valence (but in metal hydrides, H is -1 valence, such as NAH, CAH2, etc.).

3. O is generally -2 valence (but in peroxides, O is -1 valence, such as Na2O2, H2O2, etc.).

4. The charge number of the ion = its valence number, such as CI- is -1 valence, S2- is -2 valence OH- overall is -1 valence.

5. In any substance, the sum of the valence algebra of the negative valence is 0.

Common valencies of common elements:

1 price: k, na, ag, h

2 valents: MG, ZN, CA, BA

3 valence: ALFE: +2, +3 valence.

cu: +1, +2 valence.

cl：-1 、+1、+3、+5、+7

s：-2、+4、+6

mn：+2、+4、+6、+7

n：-3、+1、+2、+3、+4、+5

Now let's find the unknown valence state according to the known valence state, such as kclo3, k must be +1 valence, o must be -2 valence, how to find cl? According to the algebraic sum of positive and negative valence is 0, that is, +1+5+3*(-2)=0, so CI is +5 valence.

NH4NO3: NH4+, the number of charges carried by the ion = its valence number, so NH4+ as a whole shows +1 valence, H must be +1, so how can N be frank and congregational? -3+4*1=+1, so nh4+ in n is -3 valent.

no3-, the overall -1 valence, o must be -2 valence, according to +5+3*(-2)=-1, so no3-medium n is +5 valence.

I hope you find the above explanation helpful.

Can you be more specific?

1.Take SO2 as an example to illustrate how the relative molecular mass is calculated.

Solution: The relative molecular mass of SO2 = = the relative atomic mass of each atom * the sum of the number of atoms = = 32 * 1 + 16 * 2 = = 64

2.Find the mass ratio of each element in the constituent compound = the relative atomic mass of the element atoms * the ratio of the number of atoms.

Find the mass ratio of hydrogen and oxygen in H2O.

Solution: In H2O h:o==1*2:16==1:83The mass ratio of each element in the compound = = the ratio of the relative atomic mass of each element * the number of atoms 3: calculate the mass fraction of an element in the substance.

Find the mass fraction of hydrogen in H2O.

Solution: In H2O, H%==(Mass of H element Relative molecular mass of H2O)*100%.

4.Calculate the mass of an element in a compound = = the mass of a substance * the mass fraction of an element, and completely electrolyze 20 grams of water to obtain how many grams of hydrogen can be obtained.

Solution: In H2O.

h%==11%

Mass of H2 ==20*11%==grams.

Valency and chemical formula are written.

1. The chemical formulas of various substances are determined by experimental methods, and a pure substance can only be represented by a chemical formula, and cannot be subjectively contrived.

2. Valence. The number of atoms of different elements in a large number of compounds is a fixed ratio, and the value that reflects this relationship is the valency.

The valency value of an element is closely related to the number of outermost electrons of its atom.

3. How to write the chemical formula of the element.

1) Elemental metals, solid non-metallic elements, and rare gas elements are represented by elemental symbols. Such as metal elements: Fe (iron), Na (sodium); Solid non-metals: S (sulfur), P (phosphorus), etc.; Noble gases: HE (helium), NE (neon), etc.

2) Polyatomic molecules such as oxygen are buried in elemental matter, and superscripts are added to the lower right corner of the element symbol to indicate how many of the atoms a molecule contains. Such as: O2 (oxygen), O3 (ozone), Cl2 (chlorine).

4. How to write the chemical formula of the compound - write the chemical formula according to the valency.

1) Generally, positive elements (or clusters) are written on the left, and negative elements (or clusters) are written on the right.

2) In metal compounds, metal elements are generally positive and non-metals are negative; In chemical compounds, oxygen is generally -2 valence and hydrogen is generally +1.

3) In a compound, the algebraic sum of the valencies of various elements is zero.

Note: 1) When marking the valence of an element, be sure to write it directly above the symbol of the element, first mark the electricality, and then the number of labels + 2cuo.

As. 2 indicates that the copper element is +2 valence in copper oxide.

2) Some elements have variable valence states, which indicate a variety of possibilities that arise when combined with other elements to form compounds.