93 Dmitri's Table-Mid

Dmitri's Table FOCUS Question How does the periodic table help us understand what makes up matter?

德米特里的周期表焦点问题周期表如何帮助我们理解物质的组成?

Organizing the Elements Are you sitting in a chair? You are probably wearing shoes. Maybe you just had lunch. That chair, your shoes, and your food are types of matter. In fact, everything that takes up space and has mass—even air—is made of matter. All matter is made of tiny components called elements— substances that can't be broken down into smaller substances. There are about 120 known elements on Earth, and researchers continue to discover new ones. To organize and keep track of them all, scientists rely on a grid called the Periodic Table of the Elements.

你正坐在椅子上吗? 你可能穿着鞋子。 也许你刚刚吃过午饭。那把椅子，你的鞋子，你的食物都是物质。 事实上，任何占据空间并有质量的东西——甚至空气——都是由物质构成的。 所有物质都是由被称为元素的微小成分组成的，这些物质不能被分解成更小的物质。 地球上已知的元素大约有120种，研究人员还在继续发现新的元素。 为了组织和跟踪所有这些元素，科学家们依靠一个叫做元素周期表的网格。

By the mid-1800s, scientists had identified sixty elements. Researchers working in different parts of the world needed a way to discuss these elements and classify them by how they behave. These groupings would eventually be shared among all scientists. A few scientists devised their own charts, or periodic tables, to organize this important data. A Russian chemist named Dmitri Mendeleev published his periodic table in 1869. His table became the most popular one, and a version of it is still in use today.

到19世纪中期，科学家已经确定了60种元素。 在世界各地工作的研究人员需要一种方法来讨论这些元素，并根据它们的行为对它们进行分类。 这些分组最终将在所有科学家中共享。 一些科学家设计了他们自己的图表，或周期表，来组织这些重要数据。 俄国化学家门捷列夫在1869年发表了他的元素周期表。 他的桌子成为了最受欢迎的桌子，它的一个版本至今仍在使用。

Dmitri's Details Figuring out how to group sixty elements was not easy, but Mendeleev invented a way to describe each of the elements and organize them in a meaningful way. Dmitri's periodic table contained two details for each element—chemical symbol and atomic weight. A chemical symbol represents the element's name with one or two letters. This symbol often comes from the Latin word for the element. For example, hydrogen is H and gold is Au. Mendeleev then listed the elements by increasing atomic weight. At the time, scientists didn't know exactly how much atoms weighed, but they were able to estimate on the basis of results from chemical reactions. We now know that the tiny atoms of each element are made up of even smaller particles. Word Wise The Latin word for gold is aurum, so the chemical symbol is Au.

弄清楚如何将60种元素分组并不容易，但门捷列夫发明了一种描述每种元素的方法，并以有意义的方式将它们组织起来。 德米特里的元素周期表包含了每种元素的两个细节——化学符号和原子量。 化学符号用一个或两个字母表示元素名称。 这个符号通常来自于表示元素的拉丁单词。 例如，氢是H，金是Au。 门捷列夫接着按增加原子量的方法列出元素。 当时，科学家们并不知道原子的确切重量，但他们能够根据化学反应的结果进行估计。 我们现在知道每种元素的微小原子是由更小的粒子组成的。 金的拉丁文单词是aurum，所以化学符号是Au。

Inside an atom is a central core called a nucleus, which holds particles called protons and neutrons. Circling the nucleus are fast-moving particles called electrons. The more particles there are inside an atom, the more weight, or mass, it has. The atomic weight of an atom is the average of the total number of protons plus neutrons in all versions, or isotopes, of that atom. An isotope of an element varies in its number of neutrons, but the number of protons stays the same. A helium atom has two protons, two neutrons, and two electrons. It has an atomic weight of about four. A gold atom has 79 protons, 118 neutrons, and 79 electrons. It has an atomic weight of about 197. It is easy to see why helium is so light and gold is so heavy. Do You Know? The particles in an atom are too small to see, even with a microscope. Scientists used electric fields and radiation the movement of energy—to discover these tiny particles.

原子内部有一个叫做原子核的核心，里面有质子和中子。 围绕原子核旋转的是快速移动的粒子，叫做电子。 原子内部的粒子越多，它的重量或质量就越大。 一个原子的原子量是该原子的所有同位素的质子加中子总数的平均值。 一种元素的同位素的中子数不同，但质子数保持不变。 一个氦原子有两个质子，两个中子和两个电子。 它的相对原子质量大约是4。 金原子有79个质子，118个中子和79个电子。 它的相对原子质量约为197。 很容易看出为什么氦这么轻，而金那么重。 你知道吗?原子中的粒子太小，即使用显微镜也看不见。 科学家们利用电场和辐射——能量的运动——来发现这些微小的粒子。

Setting the Table Mendeleev listed the elements by increasing atomic weight because the elements with similar atomic weights had similar properties. Hydrogen (H) is the lightest element on Earth, so it is first on the list. In 1869, lead (Pb) had the highest atomic weight of all the known elements, so it was last on his list. Using this method, Mendeleev predicted that new elements would be discovered He was right! Today's periodic table lists the elements by atomic number instead of atomic weight. Why? The atomic number equals the number of protons in an element, and each element has a unique number of protons. Hydrogen has 1 proton, and lead has 82. Current periodic tables continue to an element called ununoctium, which has an atomic number of 118. The atomic number appears above the chemical symbol on a periodic table square. The atomic weight is displayed below the chemical symbol. Math Moment Atoms of the element bromine have 35 protons. Half of its isotopes have 44 neutrons, and half have 46 neutrons. What is the average atomic weight of bromine?

门捷列夫通过增加原子量来列出元素，因为原子量相似的元素具有相似的性质。 氢(H)是地球上最轻的元素，所以排在第一位。 1869年，铅(Pb)是所有已知元素中原子量最高的，所以在他的清单上排在最后。 用这种方法，门捷列夫预言会发现新的元素。他是对的!今天的元素周期表是按原子序数而不是原子量列出元素的。 为什么?原子序数等于元素中的质子数，每个元素都有唯一的质子数。 氢有1个质子，铅有82个。 目前的元素周期表继续列出一种叫做ununctium的元素，它的原子序数是118。 原子序数出现在元素周期表中化学符号的上方。 原子量显示在化学符号下面。 溴元素的原子有35个质子。 它的同位素有一半有44个中子，一半有46个中子。 溴的平均原子量是多少?