化合物是由两种或两种以上不同元素按固定比例结合形成的纯净物，其化学性质与组成元素不同，组成可通过化学式（如NaCl、H₂O）表示。根据元素组成分为有机化合物（含碳，如甲烷）和无机化合物（如硫酸）；按化学键类型分为离子化合物（如NaCl）、共价化合物（如CO₂）及配位化合物（如[Co(NH₃)₆]Cl₃）。
化合物的分类体系随化学研究进展不断完善，早期侧重元素组成，现代结合分子结构与化学键特性。已知化合物数量超过300万种，每年新增约30万种，其中90%为有机化合物。非等比化合物（如合金、过渡金属氧化物）的发现突破了传统定组成概念，纯度鉴定采用色谱分析、熔程测定及光谱技术，支撑化学研究与工业应用。

Now that you've learned about atomic structure and elements let's look at chemical compounds.
现在,既然你已经了解了原子结构和元素,接下来我们来看看化学化合物·
A chemical compound is a substance made of two or more elements that are chemically bonded together in fixed proportions.
化学化合物是由两种或更多种元素通过化学键结合在一起,且以固定比例组成的物质·
Common examples are water and table salt.
常见的例子有水和食盐·
You've probably heard of H2O. That's a chemical formula for water.
你可能听说过H2O·这是水的化学式·
In the chemical formula for water the little number slightly below the letter H for hydrogen is called a subscript.
在水的化学式中,稍微低于氢元素符号H的那个小数字叫做下标·
A subscript in the chemical formula tells you how many atoms of that element are in one unit of the compound.
化学式中的下标告诉你在化合物的一个单位中该元素有多少个原子·
There is no subscript next to the O for oxygen.
氧元素符号O旁边没有下标·
That means there's only one oxygen atom.
这意味着只有一个氧原子·
We don't write the one.
我们不写1·
When there is no subscript it's understood that we mean one atom.
当没有下标时,通常意味着是一个原子·
So H2O is the formula for one unit of water.
因此,H2O是一个水分子的化学式·
The formula shows that a unit of water contains a fixed proportion of two atoms of hydrogen to one atom of oxygen.
这个化学式显示,一个水分子包含两个氢原子和一个氧原子的固定比例·
It's important to know that compounds usually have very different physical and chemical properties than the individual elements they contain.
重要的是要知道,化合物通常具有与其组成的单个元素非常不同的物理和化学性质·
For example although water is liquid at room temperature the elements hydrogen and oxygen are gasses.
例如,虽然水在常温下是液体,但氢和氧这两种元素是气体·
The next compound we'll look at is sodium chloride commonly known as table salt.
接下来我们来看一个化合物:氯化钠,通常叫做食盐·
Sodium chloride consists of sodium and chloride ions.
氯化钠由钠离子和氯离子组成·
Ions are charged particles because they have gained or lost electrons.
离子是带电的粒子,因为它们获得或失去了电子·
How many ions of sodium are there in one unit of the chemical formula for sodium chloride
氯化钠的化学式中,一个单位有多少个钠离子呢?
No subscript means there's only one sodium ion.
没有下标意味着只有一个钠离子·
And how many chloride ions
那么有多少个氯离子呢?
Again there's only one.
同样,只有一个·
So sodium chloride has a one to one ratio of sodium to chloride ions.
所以,氯化钠的钠离子和氯离子的比例是1:1·
Okay. The last example of a compound is glucose. A simple sugar your body cells use for energy.
好的·最后一个化合物的例子是葡萄糖,一种你的身体细胞用作能量的简单糖·
The chemical formula for one unit of glucose is C6H12O6.
葡萄糖一个单位的化学式是C6H12O6·
Here we can see that one unit of glucose has six carbon atoms and 12 hydrogen atoms.
这里我们可以看到,葡萄糖一个单位含有6个碳原子和12个氢原子·
How many oxygen atoms does one unit of glucose have
葡萄糖一个单位有多少个氧原子?
If you said six oxygen atoms you'd be right.
如果你说是六个氧原子,那你是对的·
In review a compound is a substance containing the chemically bonded atoms of two or more elements.
总结一下,化合物是包含两个或更多元素的化学键结合原子的物质·
A chemical formula gives the proportional number of atoms or ions of each element in a compound.
化学式给出了每种元素在化合物中的原子或离子的比例数·
And the compound usually has different physical and chemical properties than the elements it contains.
而且,化合物通常具有与其组成元素不同的物理和化学性质·
We'll explore how elements chemically bond together in the next video.
我们将在下一个视频中探索元素如何通过化学键结合在一起·
内容操作
视频
教程课件
单词卡片