什么是连锁和四价？
碳是一种非金属元素。碳在地壳和大气中的含量非常少。尽管自然界中的碳含量有限，但碳原子在生命的许多方面都极为重要。我们以及所有生物、植物和动物都是由有机化合物组成的，有机化合物是碳基化合物。
什么是有机化合物？
The compounds of carbon are referred to as organic compounds. Most organic compounds contain hydrogen, while many others have oxygen or other elements in addition to carbon. As a result, hydrocarbons (substances containing hydrogen and oxygen) and their derivatives make up the vast majority of organic compounds.
有机化合物由一大类化合物中的任何一种组成，其中一个或多个碳原子与其他元素的原子共价连接，其中最常见的是氢、氧或氮。
例如 -甲烷 (CH 4 )、乙烷 (C 2 H 6 )、乙烯 (C 2 H 4 )、乙炔 (C 2 H 2 )、乙醇 (C 2 H 5 OH)、乙醛 (CH 3 CHO)、乙醇酸（CH 3 COOH）是有机化合物的一些例子。碳化物、碳酸盐和氰化物是少数未被归类为有机物的含碳化学品。
所有生物体，如植物和动物，都含有有机化合物。所有有机化合物最初都来自从生物中获得的天然矿物质。结果，人们认为有机化合物只能在活体（植物或动物体）内产生，并且制备过程需要创造生物的“生命力”。
1828 年，一位名叫 Freidrich Wohler 的科学家反驳了有机化合物的生命力理论。尿素是一种有机化合物，以前被认为只能在动物等生物体内形成。在实验室里，
Freidrich Wohler 从无机化合物“氰酸铵”(NH 4 CNO) 合成了有机化合物尿素[CO(NO 2 ) 2 ]。结果，有机化合物合成的生命力理论被否定了。
Why organic compounds are generally Covalent?
The organic compounds have low melting points and low boiling points. Organic compounds (or carbon compounds) have low melting and boiling points, indicating that the forces of attraction between their molecules are weak. They are, therefore, covalent compounds. Furthermore, most organic compounds are non-conductors of electricity, which indicates they do not contain ions. This also shows that organic compounds are naturally covalent.
大量有机化合物的存在
目前已识别出超过 500 万种有机化合物。每天，科学家们都会制备大量新的有机化合物。有机化合物的数量超过了由所有其他元素组成的化合物的总数。
导致大量有机化合物形成的碳元素的两个特性是连接和四价，下面将进一步讨论：
串联
碳原子通过共价键相互连接形成碳原子长链或环的能力是大量有机化合物或碳化合物存在的原因之一。碳具有不寻常的特性，因为它可以与其原子形成最长的链。
Catenation is the property of the carbon element that allows its atoms to link together to form long carbon chains. We term a property catenation when an element forms bonds between its atoms to form large molecules. Self-linking is another term for catenation.
例如 -在像某些蛋白质这样的分子中，碳可能形成最长的链，包含数百万个碳原子。 连接是一种化学键，仅发生在相同元素的原子之间，这些原子具有至少两个化合价，并且彼此之间产生相对强的键。
这种性质在碳原子中普遍存在，在硫和硅原子中显着，在锗、氮原子中略有存在。结果，大量的有机化合物是由于碳元素的连锁特性。当碳原子结合时可以形成三种类型的链。如下图所示，链分为直链、支链、闭链或环状链三种。
各种碳链
四价
The carbon atom has a total of 6 electrons because its atomic number is 6. Its electronic configuration can be written as 2,4. It means the outermost shell has four electrons. To achieve a stable electronic configuration, carbon requires four electrons to achieve the inert gas configuration. So carbon follows the octet rule and makes four covalent bonds with other atoms. As a result, carbon is tetravalent, meaning it has a valency of four and can create four covalent bonds with not just carbon atoms but also with other atoms. This is referred to as carbon tetravalency.
碳具有形成极强共价键的显着特性，使碳分子极其稳定。有机化合物或碳化合物丰富的另一个原因是碳的化合价为四价，比较大。由于它的 4 价大，碳原子可以与许多其他原子形成共价键，包括氢、氧、氮、硫和许多其他原子。结果，形成了大量的化合物。
已解决的问题
问题 1：命名一些表现出连锁属性的元素。
回答：
Catenation is a property when an element forms bonds between its own atoms to form large molecules. Carbon, sulphur, and silicon exhibit the property of catenation.
问题2：为什么碳主要通过共价键形成化合物？
回答：
Most carbon compounds are non-conductors of electricity, which indicates they do not contain ions. Therefore, carbon forms compound mainly by covalent bonds.
问题3：碳氢化合物叫什么？
回答：
The name of carbon-hydrogen compounds is hydrocarbons.
问题4：有机化合物合成的生命力理论是如何被拒绝的？
回答：
It was assumed that organic compounds could only be generated within a living body and the preparation required a vital force. When Freidrich Wohler synthesised the organic compound urea from the inorganic compound ammonium cyanate, the vital force theory for organic compound synthesis was rejected.
问题5：为什么有机化合物的熔点和沸点相对较低？
回答：
Individual molecules are held together by covalent bonds in organic compounds. Molecules are attracted to each other by relatively weak forces. Since the attraction forces between molecules are weak, it takes little energy to disrupt them, resulting in low melting and boiling points for organic compounds.