Simple substance(Element Substance, pure element) is composed of the same kind of elementsPure substance。The state of an element when it exists in the form of a simple substance is called elementalFree state。Generally speaking, the properties of simple substance and its elements (especiallychemical property）Closely related.For example, many metalMetallicityBoth are very strong, so their simple substanceReducibilityVery strong.The nature differences of the simple substances of different kinds of elements are reflected most prominently in the structure.Opposite to the single substance, there are manyElement compositionIs calledchemical compound。Since "simple substance" and "element" are the same word "element" in English, many students who study chemistry in English will confuse these two concepts.
Chinese name
Simple substance
Foreign name
Elementary Substance, pure element
Scope
Free pure substance of all chemical elements
Correct expression
Simple substance is a pure substance composed of the same element
Pure substances composed of the same elements are called simple substances.The state of an element when it exists in the form of a single substance is called the free state of the element. According to this, the concept of a single substance can also be understood as: a substance composed of atoms of an element that exists more stably in the free form is called a single substance.
The simple substance must be composed of one elementPure substanceTherefore, the mixture cannot be a simple substance.An element may have several simple substances, for example, the oxygen element has oxygen (Otwo）, ozone (Othree）, tetraoxy (Ofour, a new type ofOxygen molecule）Red oxygen (Oeight）Four simple substances.Although any of these substances are simple substances, they are all of the same kindElement compositionBut oxygen mixed with ozone cannot be regarded as pure, it is a mixture of the same elements.Generally speaking, the properties of simple substances are closely related to the properties of their elements.For example, many metals have strong properties, so their simple substancesReducibilityVery strong.The nature differences of the simple substances of different kinds of elements are reflected most prominently in the structure.
Correct expression: simple substance is pure substance composed of the same element
First, the element must be a pure substance, which is composed of one substance, such as sulfuric acidsodium chloride, oxygenargon 、bromine Iodine granules, gold bullion, silver flakes, copper wires and iron ingots;
Secondly, the single substance is divided intoMonatomic moleculeA simple substance composed of and a simple substance composed of polyatomic molecules.Simple substance is composed ofElement compositionCopper and iron are simple substances, butcalcium carbonate（CaCOthree）No, because calcium carbonate is composed of three elements, C, Ca and O, it is not a simple substance, it is a compound, and the compound is also pure.
Thirdly, the same element can be combined in different ways (i.eAllotrope）。For example, C can be made of graphite,diamondEtc,If they are mixed together, they can not be said to be pure, but can only be mixtures of the same element。
Beryllium and beryllium block
SoSimple substance is a pure substance composed of the same element。
Incorrect expression:Homogeneous elementIt is composed of single substance/pure substance is single substance/pure substance is composed of only one element.
Solid metalMetal bondJunction synthesisMetallic crystal。To ensure thatcrystalThe atoms take the form of dense packing.Since there are free electrons in the crystal, all metals conduct electricity and are easy to lose electrons.
Non metallic simple substance
Boron · reduced boron crystal
Non metallic simple substances are generally combined into molecules by covalent bonds.At room temperature, manyNon metallic simple substanceAll withDiatomic moleculeIt exists in the form of hydrogen, oxygen, etc.Some elements can also form polyatomic molecules, such asozone（Othree）、Football alkene（Csixty）Etc.Can formAtomic crystalThe single substance of is solid at room temperature and hard, such as diamond.
None of the above substances has free moving electrons, so they are all electricBad conductor。The exception is graphite, which has specialLayered structure, soft and conductive.
Allotrope
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Due to the different arrangement of atoms (or molecules), or the different bonding and arrangement of atoms, the same element produces multiple simple substances.They have differentphysical property, butchemical propertybe similar.
Fluorine · Fluorine gas
Such simple substances with different properties composed of the same element are calledAllotrope。They are from the same specieschemical elementA simple substance with different composition but different properties.The property difference between allotropes is mainly manifested in physical properties, and there are also active differences in chemical properties.For example, two allotropes of phosphorus,phosphorusandWhite phosphorus, theirIgnition point240 and 40 ℃ respectively,Full combustionLater products arePhosphorus pentoxide；White phosphorus (Pfour）Highly toxic, soluble incarbon disulfideRed phosphorus (P) is non-toxic, but insoluble in carbon disulfide.Under certain conditions, allotropes can transform into each other, which is a chemical change.
Preparation
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physical isolation method
Sodium · sodium block
Physical separation method is applicable toSeparation and purificationThose existing in the state of simple substance and their impurities in somephysical property(such as density, boiling point, etc.)significant difference Element of.For example, gold panning is to extract gold by taking advantage of its high density;As another example, oxygen and nitrogen are based onliquid oxygen、liquid nitrogenThe difference in boiling point willLiquid airIt is made by fractional distillation.
usereducing agentThe method of preparing the simple substance is called reduction method.Generally, appropriate reducing agents are selected according to production scale, experimental requirements, environmental protection, safety factors, raw material sources and prices.
Electrolytic method
The preparation of active metal and non-metallic elements can be carried out byElectrolytic method。For example, electrolytic saturationNaClHydrogen production from aqueous solution andchlorine；Electrolytic metalMolten saltPreparation of Li, NaMg, Al and other metals:
Oxidation method
The method of using oxidant to produce simple substance is calledOxidation method。For example, air oxidation method is used toPyriteExtracting sulfur from, coolingSulfur vaporPowdered sulfur can be obtained.Sulfur can also be produced from natural gas.[1]
preservation
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For inactive metals, nonmetals and rare gases, they are usually used in the laboratoryGlassware；In industry, use metal utensils, plastic utensils or hydraulic cylinders to store elemental substances.However, some active elements (such as fluorine) need to be stored with specific substances, otherwise it will cause the risk of reaction with the container or leakage.
Both simple substances and compounds belong to pure substances.To judge whether a substance is a simple substance or a compound, first see whether it is a pure substance. Only a pure substance can be a simple substance or a compound.It cannot be considered that a substance composed of the same element must be a simple substance, nor that a substance composed of different elements must be a compound.for exampleWhite phosphorusandphosphorus, although bothphosphorusThey are composed of elements, but they do not belong to one kind of substance. After mixing, they belong to mixture, not pure substance.Another example is that air is composed of many elements, including oxygenhydrogenElementscarbonElements, nitrogenNoble gasElements, etc., belong to mixtures, not pure substances, let alone compounds.
Difference between the two
Conceptually, a simple substance is a pure substance composed of one element, while a compound is a pure substance composed of two or more elements;From the micro scope, the simple substance is composed of the same kind of atoms, while the compound is composed of different kinds of atoms;In nature, the single substance cannot occurdecomposition reaction, compounds can undergo decomposition reaction.
Although the number of constituent elements of simple substances and compounds is different, they can transform each other.A single substance can react with a single substance to form a compound, or with a compound to form another compound.asMagnesium stripGenerated by combustion in airmagnesium oxideAmong them, magnesium and oxygen belong to simple substances, and magnesium oxide belongs to compounds;carbon monoxideCombustion generationcarbon dioxideAmong them, carbon monoxide and carbon dioxide belong to compounds, and oxygen belongs to simple substances.Compounds can also generate simple substances through decomposition reaction, such as hydrogen peroxide decomposition, which releases oxygen and generates water at the same time.hydrogen peroxideIt belongs to compound and oxygen belongs to simple substance.
Reference meaning
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staythermodynamicsThe standard enthalpy of formation and the standard free energy of formation of the most stable single substance of each element are 0, so as to calculate the thermodynamic quantities of other substances.Since there is only one element that makes up matterStandard entropyLower than compound.
Potassium · potassium block
The oxidation number of single substance is regarded as 0.
Element Collection
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Theodore Gray talks with friends on his elemental wooden table
In the 21st century, collecting and storing chemical elements has become a hobby of people.Famous chemist and element collectorTheodore Gray （Theodore gray）He is one of the best. Since 2002, he has collected elements. Over the years, he has painstakingly collected more than 2000 specimens and objects related to elements, which can be comparable to any professional museum. Later, he has collated and published the world-famous "Visual Journey: Magic Chemical Elements" andCrazy ScienceAnd other books.Since then, more and more chemistry lovers have shown their love for chemistry by collecting elements.
