听听学科学/元素
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化学有着非常有趣的历史。在古代，思想家、哲学家和科学家之间没有明确的界限。历史上许多哲学家都进行过科学实验。他们最喜欢的实验之一是将普通金属转化为黄金。他们用各种化学物质进行实验。他们被称为炼金术士。今天我们可能会认为他们是愚蠢的哲学家。但你会惊讶地发现，著名的杰出科学家艾萨克·牛顿爵士也沉迷于炼金术。他们真诚地相信他们可以通过某种方式将其他金属转化为黄金。化学这个词，甚至化学这门科学，都源于炼金术这个词。今天，我们当然知道，在化学反应中，将一种元素转化为另一种元素是不可能的，尽管这可以通过核物理学家来完成，而且由于放射性衰变，它也自然发生。
元素是一种纯净物质，由单一类型的原子组成。元素通过其原子序数来识别。原子序数是原子核中质子的数量。已知元素共有 118 种。从 1 开始，一直到 118，每个原子序数都对应着一种独特的元素。在所有已知元素中，有 80 种是自然存在的，并且是稳定的。我们将讨论一些常用的元素。
从 1 到 118 的每一种元素都有一个独特的名称，例如氢、氧、铜和铁。除了完整的名称外，每种元素都有一个独特的符号。这些符号是标准化的，可以是一个字符或两个字符。例如，氢的符号是 "H"；氧是 "O"；氦是 "He"。同样，所有 118 种元素都有一个独特的名称和一个独特的符号。
When two or more elements combine, they form a compound. Sometimes, the element will combine with itself, to form a molecule. For example, Hydrogen in its natural state, has two Hydrogen atoms. This molecule, of naturally occurring Hydrogen, is represented as H subscript 2. We will read, H subscript 2, as H,2. For example, Oxygen in its natural state, has two Oxygen atoms. This molecule, of naturally occurring Oxygen, is represented as O subscript 2. We will read, O subscript 2, as O,2. When Hydrogen, combines with Oxygen, it forms a water molecule. Water molecule, has two Hydrogen atoms, and one Oxygen atom. This is represented, as H subscript 2, O. Water molecule, is read as H,2,O.
The properties of the compound can be, very different from the properties, of the elements. Hydrogen and Oxygen, are naturally occurring gases. Water is a liquid, available in abundance. The properties of water, are very different. from that of Hydrogen and Oxygen. So, we have to remember, when we discuss a compound, The properties of the compound, would be very different, From the properties of the elements, which constitute the compound.
We will discuss some of the elements, which we experience, in day-to-day life. This could be either, as an element, or present in a compound.
Hydrogen is the first element, in the element table. Hydrogen has a symbol, H. It has an atomic number, of 1. This means, it has 1 proton, in its nucleus. It is the lightest element, on earth. Hydrogen is a non metallic gas. It is highly flammable. It will easily burn in air. Hydrogen and Helium are the most, abundant elements, in the universe. Most of Hydrogen exists in compound, such as water, and organic compounds. For example, Glucose compound, has the formula, C,6, H,12, O,6. Most of the organic compounds, has the element Hydrogen, present in it. Hydrogen is lighter than atmospheric air. We are familiar with the Hydrogen balloon. In earlier days, airships used to be filled, with Hydrogen gas.
Helium has a symbol, H e. Helium has an atomic number, of 2. It has two protons, in the nucleus. It is an inert gas, it does not react, with other substances. It is called a Noble gas. Nobel gases do not react, with other substances. The sun and other stars, produce helium, by nuclear fusion of Hydrogen. When two Hydrogen atoms are fused, in a nuclear reaction, it forms Helium. The sun's energy comes, from this nuclear reaction.
Carbon has a symbol C. Carbon has an atomic number, of 6. It is a very common element, on earth. The Lead, in our pencil is made, of carbon. Coal is mostly carbon. Carbon is present, in all known life forms. Most organic compounds have carbon, present in them. Carbon in the human body, constitutes, about 18% of its mass. Carbon is sometimes considered, as the chemical basis, of life. Carbon cycles, in the environment, in one form or another. Most forms of Animal life, breathe in Oxygen, and breathe out, Carbon dioxide. The Carbon dioxide that we breathe out, is drawn in by plants. It converts the carbon, into bio mass. This is called, Carbon fixation. Some of the bio mass is eaten, by animals. Human beings, also consume plants, Which has carbon biomass, which is a source of food, for us. In the cells, carbon is converted, to carbon dioxide. Carbon dioxide, is transported to the lungs, by blood. We breathe out, this carbon dioxide. Which again, is taken in by plants, in a continuous cycle. In this way, Carbon is continuously cycled, in the environment. This is called, the carbon cycle.
Coal is the most familiar, form of Carbon. You may be surprised to know, that diamond is also, pure carbon. The carbon atoms in a diamond are arranged, in a crystalline form, which is what, makes a diamond, a diamond. If we burn a diamond, we will be left with ash, just like coal. An element which exists, where the atoms are organised in a different way, can have different properties. Scientists are working, on a material called grapheme, which is hundreds of times, stronger than steel. Grapheme is nothing but, a sheet of carbon atoms, which is one atom thick.
Nitrogen has a symbol of N. It has an atomic number, of 7. It is a gas. It exists as diatomic molecules, with a symbol N,2. 78% of the earth's atmosphere, comprise of Nitrogen. Nitrogen combines, with many other elements, to form compounds. One commonly used compound of Nitrogen, is ammonia. Ammonia, is a compound of Nitrogen, and Hydrogen, which is N,H,3. This is used in the pharmaceuticals industry, to produce drugs, including antibiotics. Ammonia is widely used, in fertilisers. Plants absorb this Nitrogen, from fertilisers. Nitrogen is present, in living organisms, in amino acids. Amino acids are building blocks, of protein. Nitrogen is also present, in R N A, and D N A. Thus Nitrogen, is very much part of organic life. Nitrogen fixing bacteria, absorb Nitrogen, from the atmosphere. Plants, take in Nitrogen. Animals and humans, consume plants. Nitrogen is returned to the soil, via waste. Denitrifying bacteria, release Nitrogen back, to the atmosphere. This is called, the Nitrogen cycle. Like the carbon cycle, nitrogen cycle is also important, for organic life.
Oxygen has a symbol O. It has an atomic number, of 8. It is diatomic gas, with a symbol, O,2. Oxygen is a highly reactive, non metallic element. It is an oxidising agent, and readily forms, compounds. The most common compound, of oxygen is water, H,2,O. Many of the compounds are called, oxides. Most organic substances contain, Oxygen. Oxygen exists in carbohydrates, fats, and nucleic acids, and proteins. The D N A, is an organic compound called, dinucleic acid. We all breathe in oxygen, from the atmosphere. We cannot exist without oxygen, even for a few minutes. We inhale about, 1.8 to 2.4 grams of oxygen, every minute of the day, even while sleeping. Plant life, play a crucial role, in replenishing, atmospheric oxygen. Plants take in carbon dioxide, and breathe out oxygen.
Fluorine has a symbol F. It has an atomic number, of 9. Fluorine is extremely reactive, diatomic gas. We might have heard, of the presence of fluorine, in tooth paste. Fluorine helps avoid, tooth decay. In industry, fluorine is present, in refrigerant gases. Refrigerant gases, which are chlorofluorocarbon, or C F C gases, are harmful green house gases. Green house gases are pollutants, and cause global warming. Steps have been taken, to reduce it's usage. Fluorine is present, in a familiar material, called Teflon. Teflon is used, as a non sticking coating, in cook ware.
Neon has a symbol N e. It has an atomic number, of 10. It is colourless, odourless, inert mono atomic gas. Because it does not react, with other elements, it is called, as a Noble Gas. This property, of non reactivity, is used in industry. For example, electrical bulbs, are filled with, neon gas. They are even called, neon lights.
Sodium has a symbol N a. It has an atomic number, of 11. It is a highly reactive, alkali metal. Sodium readily forms compounds, with other elements. The most common compound, of sodium, is sodium chloride, N a,C,L. This common salt is present, in all oceanic water. Some other compounds, of sodium are, sodium carbonate, N a,2, C O,3. Sodium carbonate is called soda ash. Soda ash is also known, as washing soda. It is used, as a water softener, and in detergents.
Another compound is baking soda, or sodium bi carbonate, with the formula N a,H, C O,3. It is widely used in cooking, for bread, and cakes.
Most soaps, are Sodium salts, of fatty acids.
Caustic soda is sodium hydroxide, N a, O,H. Caustic soda is used in paper, textile, and detergent industries.
Magnesium has a symbol M g. It has an atomic number, of 12. Magnesium is present in living cells, in A T P, R N A,and D N A. Medically, magnesium is used in antacids, like milk of magnesia. Milk of magnesia, is magnesium hydroxide, which is M g, O, H, 2. The O H group, is called the hydroxide. Magnesium hydroxide, has one magnesium atom, and two hydroxide molecules. So, the formula is M g in brackets, whole of O H 2. In plants, Magnesium is present, in chlorophyll.
Aluminium has a symbol A l. It has an atomic number, of 13. Aluminium is a soft ductile metal. It is a good thermal, and electrical conductor. It is corrosion resistant. Aluminium and its alloys, are widely used, in house hold utensils. It is also used, in machinery, and aerospace industries.
- 硅的符号是 Si。
- 它的原子序数是 14。
- 大多数沙子和一些岩石是由硅及其化合物组成的。
- 二氧化硅，SiO2 称为硅酸盐。
- 它在地球和其他行星上很常见。
- 硅也存在于陶瓷和瓷器中。
- 高纯硅片广泛应用于半导体电子领域。
- 它是集成电路 (IC) 的基础材料。
- 集成电路，也称为芯片，广泛应用于所有电子设备。
- 硅片用于制造太阳能电池。
- 液晶显示器 (LCD) 屏幕包含硅。
- 磷的符号是 P。
- 它的原子序数是 15。
- 火柴中含有磷
- 磷被用于制造化肥和杀虫剂。
- 在有机细胞中，磷存在于 ATP、RNA 和 DNA 中。
Sulphur has a symbol S. It has an atomic number, of 16. Sulphur has been in use, since ancient times. Sulphur was used, in medicinal mixtures, and balms. It was also used, to make gunpowder. Sulphur is used, in making fertilisers. Sulphuric acid is H 2, S O 4. It is widely used, in the chemical industry. The familiar odour, of garlic is due to sulphur.
Chlorine has a symbol C l. It has an atomic number, of 17. Chlorine is a diatomic gas. It is very reactive, and readily forms, compounds. The most common compound, is sodium chloride, common salt. Chlorine is used as a disinfectant, for example, in swimming pools. A Common plastic like P V C, poly vinyl chloride, has chlorine. Chlorine is used as a bleaching agent, which is used to remove stains, and whiten clothes. Hydrochloric acid is the common compound, of chlorine. In our body hydrochloric acid, called as gastric acid, is present in the stomach, to digest food. Hydrochloric acid has, many industrial applications.
Potassium has a symbol K. It has an atomic number, of 19. Potassium is highly reactive with water, and burns when it comes into contact, with it. Potassium is present, in all living cells. We get our potassium, from plants, vegetables, and fruits. Potassium is used, in manufacturing fertilisers.
Calcium has a symbol C a. It has an atomic number, of 20. Calcium is essential, for living organisms. Our teeth and bones are, made of calcium. Calcium, makes our bones strong. Calcium is present, naturally in milk. It is due to calcium, that bones become, visible in X rays. Our skin and flesh, allows X rays to pass through, but bones block X rays. This makes bones, visible in the x ray. Calcium hydroxide is also called, as lime. When lime, is mixed with sand, it can be used as a plaster, in construction. This technique was used, more than 1000 years back. Modern cement also has, compound of calcium Calcium carbonate, C a, C O 3 is a common compound, of calcium. Calcium carbonate is present in chalk, marble, and limestone. Calcium sulphate, C a, S O 4 is called, plaster of paris. Plaster of Paris is used, in many applications, including setting broken bones.
Titanium has a symbol T i. It has an atomic number, of 22. It is a metal with low density, but high strength. It is highly resistant, to corrosion. Titanium alloys, are widely used in jet engines, and spacecrafts. It is also used, in dental implants. Some jewellery, is also made using, Titanium.
Chromium has a symbol C r. It has an atomic number, of 24. It is a lustrous, hard and brittle metal. Its name comes from Chroma, which means colour. Many compounds of Chromium, have intense colours. This is used in paint pigments. It resists tarnishing. This property is used, in chromium plating. It is common to see, chromium plated steel, in many appliances, we use. One of the major use, of chromium, is to alloy it with steel, to produce stainless steel. Stainless steel, is widely used in domestic utensils, and appliances.
Manganese has a symbol M n. It has an atomic number, of 25. Alkaline batteries, use Manganese.
Iron has a symbol F e. It has an atomic number, of 26. It is the most common metal, found in earth. The core of the earth comprises mostly, of molten iron. It was one of the earliest metals, discovered by man. After copper and tin was discovered, iron was discovered. It was used in history to make, many useful implements. Ploughs for agriculture, chariots, weapons for warfare, used iron extensively. It was so useful to man, that it had a dramatic influence, in his life style. It was so important, that a whole period in history, is called the Iron Age.
We all commonly associate, iron with strength. Surprisingly, pure iron is soft. It is hardened by additives, like carbon etc. Steel is an alloy of iron, mainly with carbon. Even today, iron and steel is very widely used in home appliances, construction, and machinery. Iron is also present, in living organisms. Haemoglobin, in our red blood cells, has Iron. Red blood cells are involved, in transporting oxygen, in our body. Oxygen from the lungs is carried, via red blood cells, to all the cells, in the body. Iron is naturally present, in many foods. When we cut an apple, and leave it for some time, We notice that the exposed portion, turns brown. This is due to the iron, getting oxidised, to iron oxide.
Copper has a symbol C u. It has an atomic number, of 29. It is a ductile metal. It has high thermal, and electrical conductivity. Copper was one of the earliest metals, to be discovered by man. It was alloyed with tin, to manufacture bronze. Bronze has been in use, since about 4500 B C. Sumerian, and Egyptians civilisations, used this alloy, of copper and tin. Bronze was used to make utensils, tools and implements. It was used to make, weapons for war fare. Bronze was also used, to make beautiful pieces, of art sculptures. The use of bronze profoundly, changed the life style, of historic people. It was so important, that a whole period in history, of human beings, is called the Bronze Age. The Bronze Age came after, the stone age. Before bronze was discovered, people were using stone tools. This period was called the Stone Age.
Zinc has a symbol Z n. It has an atomic number, of 30. Zinc is an anti Corrosive metal. It is used to coat iron, to prevent corrosion. This is known as galvanised Iron, or G I sheets. Galvanised Iron is used, as a roofing material.
Silver has a symbol A g. It has an atomic number, of 47. It is a white lustrous metal. It has the highest electrical conductivity, of any element. It has the highest thermal conductivity, of any metal. Silver is a precious metal, used in coins, and jewellery.
Tin has a symbol S n. It has an atomic number, of 50. Tin is a silvery, malleable metal. It is one of the earliest metals, discovered by man. It was alloyed with copper, to make bronze. Tin is not easily oxidised. It is used to coat, other metals. Tin and "Lead" are mixed, to produce solder. Solder is used in soldering, electronic circuits. Tin is also used, for storing food. Many of the items, we buy in the market, come in tin cans.
Iodine has a symbol I. It has an atomic number, of 53. Iodine is a violet coloured element. Minute quantities of iodine, is required for human beings. Lack of it, can cause intellectual, and developmental disabilities. Iodine deficiency, used to affect, millions of people. To avoid this, a small quantity of iodine, is added to common salt. This is called, Iodised salt.
Tungsten has a symbol W. It has an atomic number, of 74. It is a hard rare metal. Tungsten is used to produce, tungsten carbide. Tungsten carbide, is one of the, hardest metals. This is used to produce knifes, drills, saws, abrasives, cutting tools. Tungsten, has got a very high melting point. It is useful for producing, rocket nozzles. Tungsten filament is used, in making incandescent lamps or bulbs, because it does not, melt at high temperatures. Tungsten alloys are widely used, in automotive, and aero space industries.
Platinum has a symbol P t. It has an atomic number, of 78. It is a dense, malleable ductile metal. It is one of the rarest elements, on the surface of the earth. It is the least, reactive metal. It is used in catalytic converters, for vehicle emission control. Vehicles emit polluting gases, like carbon monoxide, which are harmful for life. Catalytic converters, in the exhaust pipe of vehicles, Converts hydro carbons, Carbon monoxide, and nitrogen oxide, to less harmful gases. Platinum is also used, in making jewellery.
Gold has a symbol A u. It has an atomic number, of 79. Gold is a soft, malleable ductile metal. It has a bright yellow colour, and lustre. It does not tarnish easily. Gold is a precious metal, which has been in use for a long time, to make coins, and jewellery. Though gold is of no use for human beings, it is always been associated, with wealth and money. Gold has been hoarded, as a source of wealth, for ages. It was used in trade, as an exchange for other materials, useful for human beings. Most of the gold produced, goes for making of jewellery, coins, bars etc. India is the largest consumer, of gold, in the world.
Mercury has a symbol H g. It has an atomic number, of 80. Mercury is a heavy, silvery metal. Is the only metal, which is in liquid form, at room temperatures. It is used in thermometers, to measure temperature. Mercury gas is used, in fluorescent lamps, or bulbs. Mercury gas is also used, in C F L, or compact fluorescent lamps. Fluorescent lamps are more energy efficient, than incandescent lamps. Compact fluorescent, is more energy efficient, than fluorescent lamps. Mercury is poisonous, for human beings. For this reason, bulbs and other appliances, using mercury, Have to be recycled, or disposed off, with great care. Mercury dissolves other metals, like gold, and silver.
Lead has a symbol P b. It has an atomic number, of 82. Lead is very heavy, and malleable metal. Lead is used in solders, along with tin. Solder is used extensively, in soldering electronics circuits. Lead is used, in Lead acid batteries. Due to its heavy weight, Lead is used in making bullets. Lead like mercury, is poisonous, and should be recycled. The element which has the highest atomic number, and is stable, is Lead. Elements with atomic number, greater than 82, tend to be radioactive, and unstable.
Radium has a symbol R a. It has an atomic number, of 88. Radium, is an alkaline metal. It is highly radioactive. The scientist Marie Curie, who discovered Radium, Unfortunately died, from radium exposure. Her notes and books are preserved, in Lead containers, to prevent harm, to visitors.
Uranium has a symbol U. It has an atomic number, of 92. Uranium is a radioactive substance. It was used, to make the first atomic bomb, dropped on Hiroshima. Even today, many nuclear weapons are made, with uranium. Uranium is also be used, for peaceful purposes. It is used in nuclear power plants, for producing electricity.