Atomic group - adomain

Basic introduction

The charged atomic group is also called the root or group, such as hydroxide OH^-, nitrate NO3^- , Carbonate CO₃^2-, sulfate SO₄^2-, chlorate ClO₃^-, phosphate PO₄^3-, bicarbonate HCO₃^-, ammonium root NH₄⁺ etc. It is worth noting that: A group of atoms cannot exist independently, but is only a component of a compound. A group of atoms participates in the reaction as a whole in the solution. Various atomic groups have their own characteristic reactions, such as CO₃^2- when it meets acid to become CO2, SO₄^{2-< /sup>In case of Ba²⁺, a white precipitate insoluble in dilute nitric acid will be produced, and OH^- will make the phenolphthalein test solution red. The characteristic response can be used to test the existence of roots. Pay attention to distinguish between manganate MnO₄^2- and permanganate MnO₄^-. The composition of the two is the same, but Among them, the valence of manganese is different, so the root valence is different, the manganese in the manganate radical is +6, and the manganese in the permanganate radical is +7. There are also metaphosphate PO₃^- and phosphite PO₃^3-, where the former is phosphorus +5 valence, the latter phosphorus is +3 valence. The valence of the atomic group is equal to the algebraic sum of the valences of the elements in the root.}

Features

The unique properties of atomic clusters stem from their structural characteristics. Because of their small size, the proportion of atoms on the surface is extremely high. The spin state and the force between atoms are completely different from the atoms in the bulk phase. The properties of the material are closely related to the surface properties of the internal unit. For example, just by adjusting the size of the clusters, the material properties are greatly different. A cluster of 10 iron atoms is 1000 times more efficient than a cluster of 17 iron atoms in catalyzing ammonia synthesis.

Another effect that accompanies size is the quantum effect. The study of atomic clusters has proved many hypotheses and predictions of quantum mechanics and raised countless more interesting new questions. For example, in a polyhedral cluster composed of pure metal atoms, only when the number of atoms is a "magic number series", the structure is stable, and it will not be destroyed even when heated to a liquid state. The same "magic number series" has long been known in the law of element periodicity, but its theoretical explanation is still inconclusive.

The scientific research of clusters is in a stage of vigorous development. In addition to the great theoretical significance, the practical application of atomic clusters in sound, electricity, light, magnetism, etc. is the direction of people’s efforts. .

Pay attention to understanding

(1) Atomic group is a part of the molecule. In a compound composed of three or more elements, the molecule often contains a certain group of atoms.

(2) The atomic group does not remain unchanged in any chemical reaction. In some chemical reactions, atomic groups will change. For example, in the reaction, the chlorate radical in potassium chlorate changes.

(3) Atomic group is usually called "root" or "root ion". When writing the atom group symbol, the charge it carries should be indicated, such as: ClO₃^-, SO₄^2-, OH^-, NH₄⁺, etc., do not treat the atomic group symbol as a chemical formula, such as sulfate (SO_{4 sub>^2-) mistaken for sulfur tetroxide.}

Corresponding substances

Acid and salt

Among the atomic groups, most of them are acid radicals. If you want to make it into the corresponding acid, generally add the corresponding number of hydrogen atoms before the acid radical. If nitrate NO3- turns into nitric acid, it is HNO3, and sulfate radical SO42- turns sulfuric acid into H2SO4. The same is true for salt, except that the metal or ammonium root is added before the acid root.

Organic acid radicals become organic acids or corresponding salts. When writing chemical formulas, pay attention to the fact that hydrogen or metal is written before the acid radicals.

Alkali

Alkali is the addition of metal elements before the hydroxide radical OH^-.

Ammonia

Ammonium root is special. Because it has a valence of +1, it becomes the corresponding substance by removing one hydrogen and turning into ammonia NH₃

cyanide

Atomic group