1. Change of substance: physical change: no change of other substances. Chemical change: a change that produces other substances.

Chemical changes and physical changes often occur at the same time. When a substance changes chemically, it must be accompanied by physical changes; Physical changes do not necessarily occur at the same time as chemical changes. The three-state changes of matter (solid, liquid and gas) are physical changes. When a substance changes physically, only the interval between molecules changes, but the molecules themselves do not change; When a chemical change occurs, the molecule is destroyed and the molecule itself changes. Characteristics of chemical changes: changes in other substances.

2. The nature of the material (such words as "can ……" and "can ……" are often used in statements describing the nature).

Physical properties: color, state, smell, melting point, boiling point, hardness, density and solubility.

Chemical properties: properties expressed through chemical changes. Such as reducibility, oxidation, acidity, alkalinity, flammability and thermal stability.

The chemical properties of elements are most closely related to the number of electrons in the outermost layer of atoms. The number of electrons in the outermost layer of an atom determines the chemical properties of an element.