(l) From the atomic structure, the outermost electron number of metal elements is less, generally less than 4; However, nonmetallic elements have more electrons in the outermost layer of atoms, generally greater than 4.
(2) From the chemical properties, the atoms of metal elements are easy to lose electrons in chemical reactions, showing reducibility, and are often used as reducing agents. Atoms of nonmetallic elements are easy to acquire electrons in chemical reactions, which show oxidation and are often used as oxidants.
(3) From the physical properties, there are many differences between metals and nonmetals, mainly:
① Generally speaking, simple metal has metallic luster, and most metals are silvery white; Non-metallic simple substances generally have no metallic luster and various colors.
(2) Metals except mercury are liquid at room temperature, and all other metals are solid at room temperature; Non-metallic simple substances are mostly gaseous at room temperature, and some are liquid or solid.
Generally speaking, the density and melting point of metals are high; On the other hand, nonmetals have low density and melting point.
(4) Most metals are malleable and can conduct heat and electricity; On the other hand, nonmetals have no ductility and cannot conduct heat and electricity.
It must be clear that the above differences are "general cases" or "most cases", not absolute. In fact, there is no absolute boundary between metals and nonmetals, and their properties are not completely separated. Some nonmetals have the characteristics of some metals. For example, graphite is non-metallic, but it has a gray-black metallic luster. It is a good conductor of electricity and can be used as a reducing agent in chemical reactions. Another example is that silicon is nonmetallic, but it also has metallic luster. Silicon is neither a conductor nor an insulator, but a semiconductor. There are also some metals with some nonmetallic properties, such as antimony. Although it is a metal, it is very brittle, and gray antimony has a low melting point and is volatile. , are non-metallic properties. The atomic structure of metal elements is characterized by the small number of electrons in the outermost layer, generally 1-3, which is easy to be lost in chemical reactions, thus making the second outer layer the outermost layer, usually reaching a stable structure of 8 electrons. This characteristic of atomic structure determines the properties of metals.
Physical properties: metal has metallic luster, opacity, easy heat transfer and conductivity, and can be drawn into filaments, spread into thin sheets and molded into various shapes. When many metals (free state and their combined state) burn on the flame, the flame will show a special color, according to which the existence of a certain metal or metal ion can be judged. For example, sodium is yellow, potassium is light purple (observed through blue cobalt glass), calcium is brick red, and copper is green. Metals also have different densities, melting points and hardness. For example, the density of lithium Li is the lowest (only 0.534 g/cm3, 20℃), the melting point of mercury Hg is the lowest -38.87℃, and the melting point of tungsten is as high as 3370℃.
Chemical properties: When metals combine with oxidation, metal oxides are formed. When active metals (such as K, Ca, Na) are combined with active nonmetals (such as F, O, Cl, etc.). ), metal atoms lose electrons and become cations, non-metal atoms gain electrons and become anions, and anions and cations form ionic compounds through electrostatic interaction. Such as NaCl, MgO and so on. The displacement reaction of metal with acid and salt solution follows the order of metal activity. That is, the metal before the metal active sequence hydrogen reacts with non-oxidizing acids such as hydrochloric acid, dilute sulfuric acid and phosphoric acid to produce hydrogen. In the reaction, metal atoms lose electrons and become cations, hydrogen ions H+ in the acid gain electrons and become hydrogen atoms, and hydrogen atoms combine to form H2 and release it. In the replacement reaction between metal and salt solution, the metal in front of the metal activity sequence can replace the metal in the back from its salt solution. In the reaction, the atoms of the front metal lose electrons and become cations, and the ions of the back metal gain electrons and become atoms, and several atoms gather into metal precipitates. For example:
Fe+H2SO4=FeSO4+H2↑
Iron+copper sulfate = ferrous sulfate+copper
At present, there are more than 80 kinds of metal elements found. Metals are widely used and classified in different ways. According to the density, it can be divided into light metals and heavy metals, and those whose density is less than 4.5 g/cm 3 are called light metals, such as KCa, Na, Mg, Al, etc. Densities greater than 4.5g/cm3 are called heavy metals, such as copper, nickel and lead. Metals can be divided into active metals and inactive metals according to their activity. Iron, iron, chromium and manganese are often called ferrous metals in metallurgical industry, and the rest are called nonferrous metals. In addition, metals are divided into common metals such as iron and aluminum and rare metals such as zirconium, hafnium, niobium, molybdenum and molybdenum.
Among the 109 nonmetallic elements discovered so far, nonmetallic elements account for 16. The atomic structure of nonmetallic elements is characterized by 4-7 electrons in the outermost layer (hydrogen is 1 and boron is 3), so it is easy to combine electrons in chemical reactions and achieve a relatively stable 8-electron structure. Simple materials composed of nonmetallic elements is called nonmetal. Non-metals generally have no metallic luster and are not easy to conduct heat and electricity (except graphite). At room temperature, they are solid (such as C, S, P, B, Si), liquid (such as Br2) or gas (such as H2, O2, N2, F2, Cl2), generally fragile (referring to solid) and have low density. The chemical properties of nonmetals are: easy to react with oxygen to form nonmetallic oxides. Most nonmetallic oxides are acidic oxides, and their corresponding hydrates are acids, such as S-SO2-H2SO4. Non-metallic elements combine to form valence compounds, such as HCl and CO2. Active nonmetals combine with active metals to form ionic compounds, such as calcium chloride. Non-metals react with hydrogen to generate gaseous hydrides, such as hydrogen chloride, hydrogen chloride gas, water vapor, etc.
There is no absolute boundary between nonmetal and metal. For example, silicon has both metallic and nonmetallic properties.