材料导论 (2)

Module 2 Primary Bonds
Hello, welcome to introduction to materials. Today we are going to study module 2,the Structure of Materials.
Why we need to study this module? As mentioned in Module 1, one important goal of this course is to understand the relationships among structure–properties –processing and performance of the materials, which are the four elements of materials science and engineering, as shown in this Materials Science Tetrahedron. The first element we need to learn is structure. Module 2 lays the foundation for us to understand the fundamental structures of all materials. Let’s start the journey.
译文：
大家好，欢迎来到《材料导论》课程。

今天我们将学习第二章—材料结构。

为什么要学习这章？在第一章中提过，这门课程的一个重要目标就是要理解材料的结构、性能、加工和应用之间的联系，这四者的关系正如图中‘材料科学四面体’所示，是材料科学与技术的四要素。

其中第一个我们要学习的要素就是结构。

学习第二章将会为我们理解所有材料的基本结构打下基础。

让我们开始学习的旅程吧。

Materials have different levels of structure, from subatomic to atomic, microscopic to macroscopic. Module 2 deals with the atomic structure and crystalline structure of materials.
This module is divided into four sections: 2.1 Atomic Structure and Interatomic Bonding;
2.2 Solid State; 2.3 Structure of Crystalline Solids; 2. 4 Imperfections in Solids. Let’s begin with the first section 2.1 atomic structure and interatomic bonding.
Before studying the interatomic bonding, you need to self-study atomic structure in advance. You can find the study materials in the course self-study materials.
译文：
材料有不同层次的结构，从亚原子到原子，从微观到宏观。

第二章学习的是材料的原子结构和晶体结构。

这章将分为四节：2.1原子结构及与键合；2.2固态；2.3晶体的结构；2.4晶体缺陷。

让我们开始第一节的学习——原子结构及键合
在开始学习原子键合之前，你需要提前自学原子结构，可以在课程的自学材料里找到学习所需材料。

有缘学习更多驾卫星ｙｇｄ３０７６
Let’s look at two materials you are familiar with. One is diamond which is a gemstone; another is graphite, which is a lubricant, and you can find it in pencils. Both diamond and graphite are made of the same chemical composition, that is carbon. But they behave differently. Diamond is the hardest naturally occurring material known to man and is a poor electrical conductor, while graphite is soft and a good electrical conductor. Why? Let’s find out the answer.
译文：
首先来看看我们所熟悉的两种材料。

一个是钻石（一种宝石）；另一个是石墨（可用作润滑剂，是铅笔芯儿的主要成分）。

这两种材料都是由同一种化学元素组成的—碳。

但是两者的性能表现却截然不同，钻石是人类发现的最硬的天然材料，而且是一种绝缘材料；相比之下，石墨是一种软的导电材料。

这是为什么呢？让我们一起来寻找答案吧。

Interatomic bonding can be classified into primary bonding and secondary bonding, we will learn how they are formed and their characteristics. And what is more how bonding affects the properties of materials.
译文：
原子键合的方式分为主价键和次价键。

我们将学习它们是如何形成的和他们的特性，还有键型如何影响材料的性能。

First let’s compare Primary bonding and secondary bonding. Primary bonding is the intramolecular forces, that means forces within a molecule, the bonding involves electron transfer or sharing, and they are very strong.
While secondary bonding is the intermolecular forces, that means the forces between two molecules. They are weak.
For example, within the Pentane molecules, five Carbon atoms bonded to 12 hydrogen atoms by strong covalent bonding, which is one type of the primary bonding; between pentane molecules, are weak intermolecular forces.
译文：
首先来比较主价键和次价键之间的区别。

主价键是分子内作用力，也就是分子内原子通过共享和交换电子形成，这种键很强。

次价键是分子间作用力，是通过两分子之间的作用力形成，这种键很弱。

例如，在戊烷分子中，五个碳原子与十二个氢原子之间形成共价键（是一种主价键）；两个戊烷分子之间，是弱的分子间作用力。

Primary bonding is divided into three groups. One is covalent bonding, which is the sharing of electrons, the second is ionic bonding, involving the transfer of electrons, the third is metallic bonding, which is the swarming of electrons.
译文：
主价键有三种，一个是共价键，是两个原子通过共享电子形成的；第二个是离子键，通过交换电子产生的；第三个是金属键，通过电子云集方式形成的。

Two hydrogen atoms bond to each other by covalent bonding. In covalent bonding, electrons are shared between adjacent atoms, to saturate the valency. The key word to describe the feature of covalent bonding is sharing.
More examples of covalent bonding are some ceramics, and organic compounds.
译文：
氢气分子中两个氢原子通过共价键连接。

在共价键中，为了使化合价饱和，电子在两相邻的原子间共享。

描述共价键特性的关键词是“共享sharing”。

以共价键结合的物质有陶瓷和有机化合物。

The most important covalent bonding materials are organic compounds. Hydrocarbons contain only carbon and hydrogen, and are the simplest organic compounds. For examples: methane which has four single covalent bonds, ethylene contains a double bond, acetylene contains a triple bond.
译文：
有机化合物是一种最重要的以共价键键合的材料。

烃类是最简单的有机化合物，它只含有碳和氢两种元素。

例如甲烷（含有四个单键），乙烯（含有一个双键），乙炔（含有一个三键）。

How to name covalent compounds? Covalent compounds are named according to the numbers of each element. The number of each element is indicated by the Latin prefix (mono, di, tri, tetra...).
For example: carbon dioxide, nitrogen monoxide, dinitrogen pentoxide, OXIDE is originated from ox ygen, by taking the first syllable of oxygen OX plus ide.
译文：
如何命名共价键化合物？共价键化合物是根据每种元素的数量命名的，每种元素的数量用拉丁前缀表示（mono, di, tri, tetra..）。

例如，二氧化碳，一氧化氮，五氧化二氮等。

氧化物（OXIDE）就是氧（ox ygen）的第一个音节Ox加上ide形成的。

The second type of primary bonding is ionic bonding. For example Sodium Chloride (NaCl), Na loses one electron; Cl gains one electron. That means electrons are transferred from sodium to Cl, and they become cation, and anion. The key word to describe ionic bonding is transferring. Examples of ionic bonding are inorganic compounds, like NaCl, MgO.
译文：
第二种主价键是离子键。

例如氯化钠中，钠失去一个电子，氯获得一个电子，电子从钠转移到了氯，他们分别形成阳离子和阴离子。

描述离子键的关键词是“转移transferring”。

无机化合物就是一种离子键化合物，例如氯化钠，氧化镁。

How to name inorganic compounds? First you need to know the names of cations and anions. The cation has the same name as the element. The anions name is derived from the name of the element by taking the first syllable and adding "ide''.The compound is named by placing the name of the cation first followed by the anion's name. For instance, calcium fluoride CaF2.
Here list some common anions names, for you to memorize, fluoride, chloride, oxide, nitride, carbide. We will use these names often in the following modules.
译文：
如何命名无机化合物？首先要知道阳离子和阴离子的名字。

阳离子的叫法和其元素的名字相同。

阴离子是其元素名字的第一个音节加上“ide”。

化合物起名时，阳离子名字放在前，阴离子名字在后，例如calcium fluoride（氟化钙）。

下面列出了一些常用的阴离子，以方便大家记住，fluoride氟化物，chloride氯化物，oxide氧化物，nitride氮化物，carbide碳化物。

接下来的几个章节中会经常用到这些名字。

Metals contain 1, 2, or 3 valence electrons, which are weakly bonded to the nucleus. These Valence electrons are detached from atoms, and spread in an 'electron sea' that ‘glues’ the ions together. The electrostatic force between the cation and the electron cloud is called metallic bonding. The key word to describe metallic bonding is swarming.
Metallic bonding have free or delocalized electrons which can move in three dimensions, and their bonds are non-directional, which allows atoms to pack closely. You will see how these features will affect the properties of metals later.
Metallic bonding is found in metals. Some common metals are Iron, Aluminum, Copper etc.
译文：
金属含有1，2或者3个价电子，这些电子与原子核之间作用力小，容易从原子中脱离，游离到一片电子海洋中，从而把离子“粘合”到一起。

阳离子和电子云之间的作用力称为金属键。

描述金属键的关键词是“云集swarming”。

金属键含有可以在三维空间移动单位自由或离域电子，这些键不具有方向性，允许原子紧密堆积，以后你会看到这些特点将如何影响金属的特性的。

金属键存在于金属中。

一些常见的金属有铁、铝、铜等。

To sum up, primary bonding can be classified into three types: the covalent bonding which is the sharing of electrons; the ionic bonding, which is the transfer of electrons; and the metallic bonding, which is the swarming of electrons.
Before the end of this part, think the following questions, using today’s knowledge to explain. Why are metals good conductors of both electricity and heat, while ionically and covalently bonded materials are typically electrical and thermal insulators? Why are ceramics brittle, while metals are ductile? Now it is your turn to think about it.
译文：
总结一下，主价键有三种：共享电子的共价键；交换电子的离子键；电子云集的金属键。

在结束之前，想一想下面的问题。

用今天所学的内容解释为什么金属既导电又导热，离子键和共价键材料却是典型的电、热绝缘体？为什么陶瓷很脆而金属却有韧性？现在轮到你来动脑思考了。