碳(carbon)
化学元素，周期表中IVa族非金属，化学符号C，原子序数6。碳在自然界中分布虽广，但储量并不特别丰富，在地壳中仅占0.2%，然而其化合物却比其他元素所形成的化合物的总和还多，已知的就有好几百万种。一般稳定的同位素是碳－12；另一个稳定的同位素是碳－13，是天然碳的1%。碳－14是五种放射性同位素（参阅radioactivity）中最稳定和最有名的一种，半衰期为5,730年，在碳－14年代测定法和放射性追踪研究中十分有用。元素碳以三种形式存在：金刚石、石墨和碳黑（包括煤炭、炭和焦炭），其物理特性各不相同。每个碳原子形成四种键合（4个单键、2单1双键、2个双键，或1单3双键）和至多四个其他原子，可产生多种链形、分枝状、圆形和三度空间的结构。对碳的化合物的研究已构成了一个特殊的化学领域，即有机化学。碳跟氢、氧、氮以及某些其他元素，形成约占生命机体物质18%的化合物，如蛋白质、碳水化合物、类脂化合物和核酸。生物化学是研究这些化合物如何合成、分解，以及它们如何与其他有机体发生联系。生物体消耗碳的同时又将碳送回到它们的环境中的这一系列过程构成了碳循环。碳以二氧化碳的形式约占地球大气体积的3%。它溶解於所有天然水中。碳在地壳中以碳酸盐的形式存在於大理石、石灰石、白垩等岩石中，以碳氢化合物的形式（化合物仅含碳和氢）存在於煤、石油和天然气中。海洋中含有大量分解的二氧化碳和碳酸盐。
English version：
carbon
Nonmetallic chemical element, chemical symbol C, atomic number 6. The usual stable isotope is carbon-12; carbon-13, another stable isotope, is 1% of natural carbon. Carbon-14 is the most stable and best known of five radioactive isotopes (see radioactivity); its half-life of approximately 5,730 years makes it useful in carbon-14 dating and radiolabeling of research compounds. Carbon occurs in three allotropes: diamond, graphite, and carbon black (amorphous carbon), including coal, coke, and charcoal. Carbon forms more compounds than all other elements combined; several million are known. Each carbon atom forms four bonds (four single bonds, two single and one double bond, two double bonds, or one single and one triple bond) with up to four other atoms. Multitudes of chain, branched, ring, and three-dimensional structures can occur. The study of these carbon compounds and their properties and reactions is organic chemistry. With hydrogen, oxygen, nitrogen, and a few other elements whose small amounts belie their important roles, carbon forms the compounds that make up all living things: proteins, carbohydrates, lipids, and nucleic acids. Biochemistry is the study of how those compounds are synthesized and broken down and how they associate with each other in living organisms. Organisms consume carbon and return it to the environment in the carbon cycle. Carbon dioxide, produced when carbon is burned, is about 0.03% of air, and carbon occurs in the earth's crust as carbonate rocks and the hydrocarbons in coal, petroleum, and natural gas. The oceans contain large amounts of dissolved carbon dioxide and carbonates.