noble center_noble center 诺德中心

noble center_noble center 诺德中心 _noble center 诺德中心

       noble center是一个值得探讨的话题，它涉及到许多方面的知识和技能。我将尽力为您解答相关问题。

1.重力指什么？

2.求翻译一段文字，汉译英的，高手快来啊，感激！

3.关于国庆的英语作文

4.化学元素周期表图规律特点，用英文叙述

5.适合背诵的英语美文10篇文章汇总

重力指什么？

       重力，是由于地球的吸引而使物体受到的力，叫做重力（gravity），生活中常把物体所受重力的大小简称为物重。重力的单位是N，但是表示符号为 G.公式为：G=mg。m是物体的质量，g一般取9.8N/kg。在一般使用上，常把重力近似看作等于万有引力。但实际上重力是万有引力的一个分力。重力之所以是一个分力，是因为我们在地球上与地球一起运动，这个运动可以近似看成匀速圆周运动。我们作匀速圆周运动需要向心力，在地球上，这个力由万有引力的一个指向地轴的一个分力提供，而万有引力的另一个分力就是我们平时所说的重力了在物理学上，万有引力是指具物体之间加速靠近的趋势。万有引力是自然界的四大基本相互作用之一，另外三种相互作用分别是电磁相互作用、弱相互作用及强相互作用。万有引力是上述相互作用中作用力最微弱的，但是在超距上万有引力仍然具有较大吸引力的作用。在经典力学中，万有引力被认为因引力场发生作用。在广义相对论上，万有引力来源于存在质量对时空的扭曲，而不是引力场的作用。在量子引力中，引力微子被假定为重力的传送媒介。前不久一项实验推翻了引力场存在的猜测。

       地球的吸引作用使附近的物体向地面下落。万有引力是太阳系等星系存在的原因；没有万有引力天体将无法相互吸引形成天体系统。万有引力同时也使地球和其他天体按照它们自身的轨道围绕太阳运转，月球[ Clark, John, O.E.（2004）．The Essential Dictionary of Science．Barnes & Noble Books．ISBN 0760746168．]按照自身的轨道围绕地球运转，形成潮汐，以及其他我们所观察到的各种各样的自然现象。

       编辑本段基本概念及成因

       由于地球的吸引而使物体受到的力，叫做重力[1]。方向总是竖直向下，不一定是指向地心的（只有在赤道和两极指向地心）。地面上同一点处物体受到重力的大小跟物体的质量m成正比，同样，当m一定时，物体所受重力的大小与重力加速度g成正比，用关系式G=mg表示。通常在地球表面附近，g值约为9.8牛每千克，表示质量是1千克的物体受到的重力是9.8牛。(9.8牛是一个平均值；在赤道上g最小，g=9.79N/kg；在两极上g最大，g=9.83N/kg。牛是力的单位，字母表示为N，1N大约是拿起两个鸡蛋的力)

       物体的各个部分都受重力的作用。但是，从效果上看，我们可以认为各部分受到的重力作用都集中于一点，这个点就是重力的等效作用点，叫做物体的重心。重心的位置与物体的几何形状及质量分布有关。形状规则，质量分布均匀的物体，其重心在它的几何中心，但是重心的位置不一定在物体之上。

       重力并不等于地球对物体的引力。由于地球本身的自转，除了两极以外，地面上其他地点的物体，都随着地球一起，围绕地轴做近似匀速圆周运动，这就需要有垂直指向地轴的向心力，这个向心力只能由地球对物体的引力来提供，我们可以把地球对物体的引力分解为两个分力，一个分力F1，方向指向地轴，大小等于物体绕地轴做近似匀速圆周运动所需的向心力；另一个分力G就是物体所受的重力其中F1=mrw^2(w为地球自转角速度，r为物体旋转半径)，可见F1的大小在两极为零，随纬度减少而增加，在赤道地区为最大F1max。因物体的向心力是很小的，所以在一般情况下，可以近似认为物体的重力大小等于万有引力的大小，即在一般情况下可以略去地球转动的影响。其中引力的重力分量提供重力加速度，引力的向心力分量提供保持随地球自转的向心加速度。

       重力大小可以用测力计测量，静止或匀速直线运动的物体对测力计的拉力或压力的大小等于重力的大小。

       编辑本段附加解释

       重力的大小除可用万有引力大小计算以外，还可以由牛顿第二定律F=ma计算，这时重力可以写成：G=mg。重力是矢量，它的方向总是竖直向下的。重力的作用点在物体的重心上。

       此外，有密度较大的矿石附近地区，物体的重力要比周围地区稍大些，利用重力的差异可以探矿，这种方法叫重力探矿。

       根据大量的实验数据，可以得出，：物体所受的重力跟它的质量成正比。重力和质量的比值大约是9.8牛/千克。

       由万有引力定律可知，G(重力）=G（万有引力常数，G≈6.67259×10^-11 米2/(千克·秒^2)）*M（地球质量）*m（受力物体质量）/R（物体距地心距离）^2。

       所以g（重力加速度）=G*M/R^2

       关于公式：在物理学中，重力公式为G=mg。

       其中，G表示重力，单位用牛顿(N)来表示，m表示质量，单位用千克（kg），g等于9.8牛/千克（9.8N/kg）

       g值在粗略计算中可为10N/kg计算因为物理学认为所有的测量都是有误差的且g值的大小随着纬度的大小而变化。如：赤道的地球纬度为0°g值为9.780，北极的地球纬度90°，g值为9.832.而且g值与高度有关，海拔越高，g值越小，反之则越大。

       重力与地面的接触面积无关

       另外，由重力与加速度的相关定义可知，重力与加速度的作用效果某些程度上是相同的。举个简单的例子：想象地球上有个电梯，现在电梯厢很高很高以致脱离了地心引力。有如下两种情况，（1）突然在电梯厢下方施加方向为竖直向下的重力（2）电梯厢忽然作竖直向上的匀变速运动，可以想象这两种情况下电梯厢内的物体的运动状态会是一样的——“啪”地一下摔在电梯厢底部。[2]

       编辑本段定义

       重力是力学中最重要、最基本的概念之一。但是，国内外各种课本及参考书对重力概念的定义不尽一致，目前对重力的定义大致有以下三类。

       重力的方向

       第一类定义很明确，重力就是指地球对物体的吸引力。重力即是力，就是矢量，其方向就是地球对物体引力的方向，即竖直指向地球中心。按这类定义，重力就成了引力的同义词，但重力并不代表万有引力。其实，这类定义只有在不考虑地球自转所引起的效果时才有意义。

       第二类定义：“地球对其附近物体吸引的力是重力”。“地球对地球表面附近物体的引力称重力”。

       第二类定义的共同特点是有“表面”、“附近”此类限制性词．这些“表面”、“附近”表达着怎样的意思呢？如只是一个区域性概念的话，那就是说只有地球表面附近的引力才称重力，除此以外，就只称引力，不再称重力了；另外，到底距地球表面多远才不算“表面”、“附近”呢？距地表大约2000m的范围内，算是附近。

       第三类定义：“质点以线悬挂并相对于地球静止时，质点所受重力的方向沿悬线且竖直向下，其大小在数值上等于质点对悬线的拉力”。“实际上，重力就是悬线对质点拉力的平衡力”。“物体在地球表面附近自由下落时，有一竖直方向的重力加速度g，产生此重力加速度的力称为重力”。

       第三类定义分别从静力学形式和动力学形式给出了重力的“操作性定义”，并暗示了重力不是纯地球引力，而是把地球自转影响考虑在内的地球引力和物体随地球绕地轴转动所受的向心力之差．这类定义美中不足的是未能明确表达出重力的主要本质，即“地球引力”这一本质因素．

       重力

       综上所述，以上三类关于重力的定义都不够确切．重力的比较确切的定义是：“随地球一起转动的物体，所表现出的、所受地球的引力，称物体的重力。”根据这种定义，重力概念的内涵有：

       （1）重力的本质来源是地球的引力。

       （2）重力是一个表观的概念，是物体随地球一起转动时受到地球的引力。

       （3）重力等于物体受地球的引力和随地球绕轴转动所需向心力的矢量差。

       (4) 重力的方向总是竖直向下的。（不是垂直向下）

       （5）重力是由于地球的吸引产生的，但不能说重力就是地球的引力。

       编辑本段重心

       重力在物体上的作用点叫做重心(center of gravity) 。地球对物体的重力，好像就是从这一点向下拉物体。若用其他物体来支持着重心，物体就能保持平衡。

       质地均匀、外形规则的物体的重心，在他的几何中心上，例如粗细均匀的棒的重心在他的中点；球的重心在球心；方形薄板的重心在两条对角线的交点。

       但是，重心不一定在重物上。

       物体的重心位置，质量均匀分布的物体（均匀物体），重心的位置只跟物体的形状有关。有规则形状的物体，它的重心就在几何中心上，例如，均匀细直棒的中心在棒的中点，均匀球体的重心在球心，均匀圆柱的重心在轴线的中点。不规则物体的重心，可以用悬挂法来确定。物体的重心,不一定在物体上。

       质量分布不均匀的物体，重心的位置除跟物体的形状有关外，还跟物体内质量的分布有关。载重汽车的重心随着装货多少和装载位置而变化，起重机的重心随着提升物体的重量和高度而变化。

       重心位置在工程上有相当重要的意义。例如起重机在工作时，重心位置不合适，就容易翻倒；高速旋转的轮子，若重心不在转轴上，就会引起激烈的振动。增大物体的支撑面，降低它的重心，有助于提高物体的稳定程度。

       编辑本段重心的影响因素

       规则几何物体∶重心在几何中心上或几何中心内

       不规则几何物体∶

       a、物体形状

       b、质量的分布

       此外，同一个物体重力的大小与所处的纬度有关。因为一切物体在地球上与地球一起运动，这个运动可以近似看成匀速圆周运动。物体作匀速圆周运动需要向心力，既一个绕地轴转动的力。而纬度低的地方所需向心力大，纬度高的地方所需向心力小。

       编辑本段重力方向的应用

       （1）重垂线：检查物体是否与地球重力垂直。

       （2）水平仪：检查桌面或窗台是否水平。

       （3）力的三要素：大小、方向、作用点。

       （4）物体所受重力跟它的质量成正比，其比值是定值，约等于9.8N/kg，在精确度要求不高的情况下可取值为10N/kg。

       （5）重力的方向总是竖直向下的（注意是竖直，不是垂直）。

求翻译一段文字，汉译英的，高手快来啊，感激！

       自我介绍

       Hello, i come from tianjin, china is one of the four municipalities directly under the 137 kilometres from beijing, is a famous international port city and the environment of tianjin city. in the bohai 经济圈 the center of northern china, is the open coastal cities, modern industry, the cradle of modern the earliest open coastal cities, our country is one of the sea and the center of industry to china. as a fourth industrial base and the third largest foreign trade port cities,Since the new liberated areas in the development of national policy and rejoin the rapid development. 2013, it will cater for the sixth session of the east asian games.

       我对你的好印象

       On tv since i see you, for your great life and values up out of respect. i think the happy life of many, especially for the others happy, he will be more happy this is a simple and pure joy, and so noble and extraordinary. i envy you your vast knowledge and looking forward to the feelings, i hope some day? how can you, i love harvard,Love her Enter to grow in knowledge,depart to better serve thy country and thy kind 我的两个小愿望

        I’d like to turn into friends with you.

       Could you teach me english

       终于打好啦，望采纳！(*^__^*) ……

关于国庆的英语作文

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       Repast environment

       XXX, dining-room USES Europe type style is decorated, dining-room has 24 repast, three hardcover, luxury room can hold about 200 guests for dinner. All the desks and chairs, pure wood dinnerware high-grade fastidious, dining-room center with the view to facilitate your TV in all kinds of programs, when repast appreciate high-fidelity surround sound can be according to your request play all kinds of music, and high quality for you to create a comfortable, unique taste, unique ideal repast environment.

       Being a VIP membership

       We can execute "new membership VIP" system, you can according to need to deal with VIP card, disposable top-up 1000 yuan, dining-room giving you 200 yuan (cost of 20%). Pre-paid 2000 yuan, 400 yuan, gifts and so on. The VIP card will be reflected in the dining-room of your noble status, more convenient repast, you will be unexpected surprise (see the VIP card using rules).

       Improving grade enjoy life, welcome to 餐厅

化学元素周期表图规律特点，用英文叙述

       National Day celebration, to show an army of military might, a country's prestige and a nation's noble spirit.

       Of the Republic passed 60 springs and autumns, the flames of years remembered. We have been suffering, we have experienced tempered, we have had bitter pursuit, and we all came off, and we have gone through the motherland, the backbone of the firm; we have had a dream, we have had lofty sentiments and aspirations, we have had numerous happiness and joy, we have had, we have experienced. We have a fear no hardship and courage of the proud nation, we have a strong backbone of the motherland proud.

       Some people say that a person without backbone, they will not stand on its feet; a country that lost its backbone, it will only yield to someone else's foot, creeping crawling. Yes, have a strong backbone of the country, will have to overcome difficulties, self-motivation can there be any difficulty will not be intimidated by courage. Over the past year, the sun and the moon walk, is tempered to withstand the days of the motherland. Snow, 4.28 crash, 5.12 Wenchuan earthquake ... ... it seems the ensuing natural disasters time and time again, the motherland in his suffering, but also for those who leave their children were in tears, heartache. Can still stand tall with the motherland,

       One with the names of five thousand years of history of civilization, China is still standing in the world, the East; the country is still strong, a faith and spirit of the Chinese nation, the country move forward stronger than ever. Disasters, disaster, you can reclamation, plug the river, can destroy our beautiful home, you can let us lose the good pro-family. However, the sons and daughters can not shake the will be able to overwhelm the backbone of our country. Backbone appear to be normal, but it is the fulcrum. It is not only a person standing pivot, but also the fulcrum of a nation Xiongqi, but also the fulcrum of a country moving forward very proudly. The backbone and sometimes invisible, but can be a sense of

       Subject of that, it is a nation and the state enterprising spirit and strength. With the unyielding as long as the backbone of the people, as long as the country has a strong backbone in, no difficulty can stop the momentum that we forge ahead and courage.

       Some say that more prosperous country disaster. Each time disaster, let each of us become more mature, and make our motherland has become stronger, we have one unwilling to yield, always strong and proud of the motherland. Yes, with a strong backbone of the country, people can enjoy a happy, elated, in order to take on the responsibility of world peace, in order to write a glorious chapter in human civilization. This past year the days passed, though bitter, but also joy. 29 th Olympic Games held in the land of China. This is the time of the greatest gathering of mankind, but also dream of the Chinese century, so that people of the world better understand China.

       Over half a century ago has also been criticized as a "sick man of Asia" Chinese people, while the exercises had been sporting Moving into the ranks of the country, demonstrates our ability to host the Olympic Games in the history of the best sporting event. During the Olympics, the Chinese people toward the Olympic spirit of respect, dignity and 204 countries and regions of the athletes, the world's friends hand in hand, heart to heart in this piece of land of old and young with a spirit of growth of the Olympic spirit, and writing "New Olympics" wonderful chapter! Beijing Olympic Games success, so that people of the world gone through many hardships to see a nation who excel through reform and opening up, has stepped into a chase Moving

       Seeking scientific, harmonious, progressive, peaceful and modern civilized country. Over the past year, the days passed, though sad, but there are surprises. Nation from the disaster is to walk out of the nation, tempered by the setbacks suffered is bound to rise up the national state. Shenzhou VII manned space flight was a complete success, not only let us see the great practice of building the motherland in the process achieved a major breakthrough, so we increased the confidence of 100 saw the group of the country's economic strength, scientific and technological strength, defense strength, and national increasing level of cohesion. The backbone of the Chinese nation and China is not bending, but indomitable, proud to stand upright with a strong backbone.

       When the time's footsteps into 2009, the motherland will never rises past six decades is a monument in our hearts and is always encouraging us to move forward the torch! "Rise up, do not want to be slaves to our flesh and blood, building into our new Great Wall ... ..." It's majestic national anthem, not correct to sing our great motherland backbone of a strong and unyielding do? Let us take the space as impetus to realize the great rejuvenation of the Chinese nation to build into our new Great Wall.

适合背诵的英语美文10篇文章汇总

       The periodic law is most commonly expressed in chemistry in the form of a periodic table, or chart. The so-called short-form periodic table, based on Mendeleyev's table, with subsequent emendations and additions, is still in widespread use. In this table the elements are arranged in seven horizontal rows, called the periods, in order of increasing atomic weights, and in 18 vertical columns, called the groups. The first period, containing two elements, hydrogen and helium, and the next two periods, each containing eight elements, are called the short periods. The remaining periods, called the long periods, contain 18 elements, as in periods 4 and 5, or 32 elements, as in period 6. The long period 7 includes the actinide series, which has been filled in by the synthesis of radioactive nuclei through element 102, nobelium. Heavier transuranium elements have also been synthesized.

       The groups or vertical columns of the periodic table have traditionally been labeled from left to right using Roman numerals followed by the symbol a or b, the b referring to groups of transition elements. Another labeling scheme, which has been adopted by the International Union of Pure and Applied Chemistry (IUPAC), is gaining in popularity. This new system simply numbers the groups sequentially from 1 to 18 across the periodic table.

       All the elements within a single group bear a considerable familial resemblance to one another and, in general, differ markedly from elements in other groups. For example, the elements of group 1 (or Ia), with the exception of hydrogen, are metals with chemical valence of +1; while those of group 17 (or VIIa), with the exception of astatine, are nonmetals, commonly forming compounds in which they have valences of -1.

       In the periodic classification, noble gases, which in most cases are unreactive (valence = 0), are interposed between highly reactive metals that form compounds in which their valence is +1 on one side and highly reactive nonmetals forming compounds in which their valence is -1 on the other side. This phenomenon led to the theory that the periodicity of properties results from the arrangement of electrons in shells about the atomic nucleus. According to the same theory, the noble gases are normally inert because their electron shells are completely filled; other elements, therefore, may have some shells that are only partly filled, and their chemical reactivities involve the electrons in these incomplete shells. Thus, all the elements that occupy a position in the table preceding that of an inert gas have one electron less than the number necessary for completed shells and show a valence of -1, corresponding to the gain of one electron in reactions. Elements in the group following the inert gases in the table have one electron in excess of the completed shell structure and in reactions can lose that electron, thereby showing a valence of + 1.

       An analysis of the periodic table, based on this theory, indicates that the first electron shell may contain a maximum of 2 electrons, the second builds up to a maximum of 8, the third to 18, and so on. The total number of elements in any one period corresponds to the number of electrons required to achieve a stable configuration. The distinction between the a and b subgroups of a given group also may be explained on the basis of the electron shell theory. Both subgroups have the same degree of incompleteness in the outermost shell but differ from each other with respect to the structures of the underlying shells. This model of the atom still provides a good explanation of chemical bonding.

       There are 18 vertical columns, or groups, in the standard periodic table. At present, there are three versions of the periodic table, each with its own unique column headings, in wide use. The three formats are the old International Union of Pure and Applied Chemistry (IUPAC) table, the Chemical Abstract Service (CAS) table, and the new IUPAC table. The old IUPAC system labeled columns with Roman numerals followed by either the letter A or B. Columns 1 through 7 were numbered IA through VIIA, columns 8 through 10 were labeled VIIIA, columns 11 through 17 were numbered IB through VIIB and column 18 was numbered VIII. The CAS system also used Roman numerals followed by an A or B. This method, however, labeled columns 1 and 2 as IA and IIA, columns 3 through 7 as IIIB through VIB, column 8 through 10 as VIII, columns 11 and 12 as IB and IIB and columns 13 through 18 as IIIA through VIIIA. However, in the old IUPAC system the letters A and B were designated to the left and right part of the table, while in the CAS system the letters A and B were designated to the main group elements and transition elements respectively. (The preparer of the table arbitrarily could use either an upper-or lower-case letter A or B, adding to the confusion.) Further, the old IUPAC system was more frequently used in Europe while the CAS system was most common in America. In the new IUPAC system, columns are numbered with Arabic numerals from 1 to 18. These group numbers correspond to the number of s, p, and d orbital electrons added since the last noble gas element (in column 18). This is in keeping with current interpretations of the periodic law which holds that the elements in a group have similar configurations of the outermost electron shells of their atoms. Since most chemical properties result from outer electron interactions, this tends to explain why elements in the same group exhibit similar physical and chemical properties. Unfortunately, the system fails for the elements in the first 3 periods (or rows; see below). For example, aluminum, in the column numbered 13, has only 3 s, p, and d orbital electrons. Nevertheless, the American Chemical Society has adopted the new IUPAC system.

       The horizontal rows of the table are called periods. The elements of a period are characterized by the fact that they have the same number of electron shells; the number of electrons in these shells, which equals the element's atomic number, increases from left to right within each period. In each period the lighter metals appear on the left, the heavier metals in the center, and the nonmetals on the right. Elements on the borderline between metals and nonmetals are called metalloids.

       Group 1 (with one valence electron) and Group 2 (with two valence electrons) are called the alkali metals and the alkaline-earth metals, respectively. Two series of elements branch off from Group 3, which contains the transition elements, or transition metals; elements 57 to 71 are called the lanthanide series, or rare earths, and elements 89 to 103 are called the actinide series, or radioactive rare earths; a third set, the superactinide series (elements 122–153), is predicted to fall outside the main body of the table, but none of these has yet been synthesized or isolated. The nonmetals in Group 17 (with seven valence electrons) are called the halogens. The elements grouped in the final column (Group 18) have no valence electrons and are called the inert gases, or noble gases, because they react chemically only with extreme difficulty.

       In a relatively simple type of periodic table, each position gives the name and chemical symbol for the element assigned to that position; its atomic number; its atomic weight (the weighted average of the masses of its stable isotopes, based on a scale in which carbon-12 has a mass of 12); and its electron configuration, i.e., the distribution of its electrons by shells. The only exceptions are the positions of elements 103 through 118; complete information on these elements has not been compiled. Larger and more complicated periodic tables may also include the following information for each element: atomic diameter or radius; common valence numbers or oxidation states; melting point; boiling point; density; specific heat; Young's modulus; the quantum states of its valence electrons; type of crystal form; stable and radioactive isotopes; and type of magnetism exhibited by the element (paramagnetism or diamagnetism).

       The layout of the periodic table demonstrates recurring ("periodic") chemical properties. Elements are listed in order of increasing atomic number (i.e., the number of protons in the atomic nucleus). Rows are arranged so that elements with similar properties fall into the same columns (groups or families). According to quantum mechanical theories of electron configuration within atoms, each row (period) in the table corresponded to the filling of a quantum shell of electrons. There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration.

       In printed tables, each element is usually listed with its element symbol and atomic number; many versions of the table also list the element's atomic mass and other information, such as its abbreviated electron configuration, electronegativity and most common valence numbers.

       As of 2006, the table contains 117 chemical elements whose discoveries have been confirmed. Ninety-four are found naturally on Earth, and the rest are synthetic elements that have been produced artificially in particle accelerators. Elements 43 (technetium), 61 (promethium) and all elements greater than 83 (bismuth), beginning with 84 (polonium) have no stable isotopes. The atomic mass of each of these element's isotope having the longest half-life is typically reported on periodic tables with parentheses.[1] Isotopes of elements 43, 61, 93 (neptunium) and 94 (plutonium), first discovered synthetically, have since been discovered in trace amounts on Earth as products of natural radioactive decay processes.

       The primary determinant of an element's chemical properties is its electron configuration, particularly the valence shell electrons. For instance, any atoms with four valence electrons occupying p orbitals will exhibit some similarity. The type of orbital in which the atom's outermost electrons reside determines the "block" to which it belongs. The number of valence shell electrons determines the family, or group, to which the element belongs.

       The total number of electron shells an atom has determines the period to which it belongs. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order (the Aufbau principle):

       Groups

       Main article: Group (periodic table)

       A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. These groups tend to be given trivial (unsystematic) names, e.g., the alkali metals, alkaline earth metals, halogens, pnictogens, chalcogens, and noble gases. Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Group 14), and these have no trivial names and are referred to simply by their group numbers.

       Periods

       Main article: Period (periodic table)

       A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends. This can be true in the d-block (or "transition metals"), and especially for the f-block, where the lanthanoids and actinoids form two substantial horizontal series of elements.

       Blocks

       Main article: Periodic table block

        This diagram shows the periodic table blocks.Because of the importance of the outermost shell, the different regions of the periodic table are sometimes referred to as periodic table blocks, named according to the subshell in which the "last" electron resides. The s-block comprises the first two groups (alkali metals and alkaline earth metals) as well as hydrogen and helium. The p-block comprises the last six groups (groups 13 through 18) and contains, among others, all of the semimetals. The d-block comprises groups 3 through 12 and contains all of the transition metals. The f-block, usually offset below the rest of the periodic table, comprises the rare earth metals.

       Other

       The chemical elements are also grouped together in other ways. Some of these groupings are often illustrated on the periodic table, such as transition metals, poor metals, and metalloids. Other informal groupings exist, such as the platinum group and the noble metals.

       Periodicity of chemical properties

       The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table. It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.

       Periodic trends of groups

       Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties. Elements in the same group also show patterns in their atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.

       Periodic trends of periods

        Periodic trend for ionization energy. Each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases.Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.

       美丽英文全集(散文卷)(双语读物)

       编译:方雪梅

       文摘:

       An ant is a wise creature for itself， but it is a shrewd thing in an orchard2 or garden.And certainly men that are great lovers of themselves waste the public. Divide with reasonbetween self-love and society； and be so true to thyself， as thou be not false to others； spe-cially to thy king and country. It is a poor centre of a man's actions， himself. It is rightearth. For that only stands fast upon his own centre； whereas all things that have affinitywith the heavens， move upon the centre of another， which they benefit. The referring of allto a man's self is more tolerable3 in a sovereign prince； because themselves are not onlythemselves， but their good and evil is at the peril of the public fortune. But it is a desperateevil in a servant to a prince， or a citizen in a republic. For whatsoever affairs pass such aman's hands， he crooketh them to his own ends； which must needs to be often eccentric tothe ends of his master or state. Therefore， let princes， or states， choose such servants ashave not this mark； except they mean their service should be made but the accessory. Thatwhich maketh the effect more pernicious is that all proportion is lost It were disproportionenough for the servant's good to be preferred before the master's； but yet it is a greaterextreme， when a little good of the servant shall carry things against a great good of themaster's. And yet that is the case of bad officers， treasurers， ambassadors， generals， andother false and corrupt4 servants； which set a bias upon their bowl， of their own petty endsand envies， to the overthrow of their master's great and important affairs. And for the mostpart， the good such servants receive is after the model of their own fortune；?

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