What is the nature of chemistry
Chemistry is a basic natural science that studies the composition, structure, properties and changing laws of substances. Its essence is to find out the laws followed when any substance changes to generate new substances. Its manifestations are the breaking of old chemical bonds and the new The formation of chemical bonds, and its constituent atoms will not change during the entire reaction process and before and after the reaction.
Among them, chemical bonds refer to the most basic particles of matter in the chemical world, the strong interaction between atoms, which includes metal bonds, ionic bonds and covalent bonds; metal bonds refer to the metal cations in metal crystals. The chemical bond formed by the interaction of free electrons; the ionic bond refers to the chemical bond formed by electrostatic interaction between anions and cations; the covalent bond refers to the chemical bond formed by the common electron pair between atoms. Therefore, if there is a chemical change, there must be the breaking of chemical bonds, which causes the breaking and reorganization of chemical bonds between the atoms involved in the chemical reaction, and is accompanied by the release or absorption of energy, but there is a change in the breaking or reorganization of chemical bonds. chemical reaction. For example: the colorless, pungent odor and corrosive covalent compound hydrogen chloride gas (HCl) dissolves in water to form a common industrial hydrochloric acid (see the figure below), and the covalent bond between H and Cl is broken. , forming free hydrogen ions and chloride ions, but no new substances are formed;
Common industrial hydrochloric acid (colorless and transparent liquid with strong pungent odor and strong corrosiveness).
Another example: when the ionic compound sodium chloride (the main component of table salt) NaCl dissolves in water to form a solution or is heated in a molten state, the ionic bond between Na and Cl is destroyed, forming free sodium ions and chloride ions, NaCl After the solution evaporates, it is reduced to a solid, which is in the form of colorless and transparent cubic crystals (see the figure below). Therefore, such processes are seen only as physical changes.
Common Sodium Chloride Crystals
Sodium Chloride Crystal Structure Model
It can be seen that chemical bonds must be broken and formed when substances undergo chemical changes, but the change of chemical bonds does not mean that chemical changes must have occurred.
It is worth noting that in the nuclear reaction, the nucleus will undergo decay, fission, fusion, etc., resulting in the change of the atom and the formation of new elements, so the above-mentioned new substances do not include nuclear reaction products.