每周分子 | Molecule of the Week

Original ACS 美国化学会 ACS美国化学会 2022-07-01

收录于合集 #每周分子 110个

每周分子：氢气

Molecule of the Week: Hydrogen

令人惊讶的是，迄今为止，“每周分子”尚未报道最小、最简单的原子和分子——氢气。氢是宇宙中最丰富的元素，约占其质量的75％。但在地球大气中，其仅有0.5–1.0ppm，同样，氢占地壳重量的0.75％；但是当然，氢是地壳表面一个很大的组成部分，主要是因为有大量的水。

英国科学家Henry Cavendish于1766年首次将氢气描述为一种元素，他称其为“易燃空气”。七年后，法国化学家Antoine Lavoisier将其命名为氢气(希腊语中为“水形成物”)。他还表明分子中有两个氢原子。

氢气在工业化学生产中极为重要。由于运输危险，因此几乎总是在使用地点制备。主要用天然气蒸汽重整(CH₄+H₂O→CO+3H₂)和其他轻烃来生产氢气。蒸汽重整过程中通过水煤气变换反应(CO+H₂O→CO₂+H₂)形成的一氧化碳通常会产生额外的氢。这两种反应都是催化反应，并且在高温和高压下进行。

篇幅所限，我们无法讨论氢气性质和用途的所有方面。但是，最近来自法国的两份报告引起了人们的兴趣：

从理论上讲，只要施加足够高的压力，就可以像其他所有元素一样，将氢制成金属。许多科学家声称可以制造金属氢，但没有一位能使科学界满意。今年早些时候，法国原子能和替代能源委员会(Arpajon)的Paul Loubeyre*、Florent Occelli和Paul Dumas使用具有新型挤压表面的砧座来达到足够的压力(>400GPa)，产生一个氢相，通过红外光谱鉴定为金属。结果与金属丰度理论计算一致。

当被燃烧用来发电或驱动车辆时，氢气是为数不多的不释放温室气体的能源之一。但就目前而言，几乎所有氢气生产都会释放二氧化碳(见上文)，全球每年约有十亿公吨。根据国际能源机构(巴黎)的报告，直到2030年之后，可再生能源水电解法的成本依然不足以让人们能够负担制备“绿色”氢气。

氢气信息速览

CAS 登记号	1333-74-0
SciFinder 命名	Hydrogen
分子式	H₂
摩尔质量	2.02 g/mol
外观	无色气体
熔点	–252.8 ºC
水溶性	1.6 mg/L (1 atm, 20 ºC)

氢气危害信息

GHS*分类：易燃气体，分类1
H220-极易燃气体
GHS分类：受压气体，压缩气体
H280-含有受压气体；加热可能爆炸

【关于每周分子】

自2001年以来，“每周分子”已成为广受欢迎的栏目。多数分子由读者推荐。每个结构都经由科学家审查，并以3-D和平面图像的形式显示，同时附有该分子简介。可以通过美国化学文摘社 (CAS) 提供的SciFinder中的CAS REGISTRY获取“每周分子”的更多信息。CAS REGISTRY中的每条物质信息都展示了物质的CAS登记号、索引名、通用名、商品名、书目信息等其他更多信息。发送邮件至motw@acs.org推荐您感兴趣的分子吧。

Surprisingly, hydrogen, the smallest and simplest atom and molecule, has not appeared in Molecule of the Week until now. Hydrogen is the most abundant element in the Universe, comprising ≈75% of its mass; but it constitutes only 0.5–1.0 ppm of Earth’s atmosphere. Similarly, hydrogen makes up 0.75 wt% of Earth’s crust; but of course, it is a much larger component of its surface, mostly because of the abundance of water.

English scientist Henry Cavendish first described hydrogen as an element in 1766; he called it “inflammable air”. Seven years later, French chemist Antoine Lavoisier gave it the name hydrogen (“water-former” in Greek). He also showed that there are two hydrogen atoms in the molecule.

Hydrogen is extremely important in industrial chemical manufacture. Because it is hazardous to transport, it is almost always generated at the site where it is used. It is produced mainly by steam-reforming natural gas (CH₄+H₂O→CO+3H₂) and other light hydrocarbons. Additional hydrogen is often generated from the carbon monoxide formed during steam reformation via the water–gas shift reaction (CO+H₂O→CO₂+H₂). Both reactions are catalytic and operate at high temperatures and pressures.

Space does not permit a discussion of all aspects of hydrogen properties and uses. But two recent reports from France are of interest:

Theoretically, it should be possible to make hydrogen, like all other elements, into a metal, given high enough applied pressure. Many scientists have claimed to make metallic hydrogen, but none have succeeded to the satisfaction of the scientific community. Earlier this year, Paul Loubeyre*, Florent Occelli, and Paul Dumas at the French Alternative Energies and Atomic Energy Commission (Arpajon) used an anvil with a new type of squeezing surface to achieve sufficient pressure (>400 GPa) to create a phase of hydrogen that was identified as a metal by infrared spectroscopy. The result agreed with theoretical calculations of metallicity.

Hydrogen is one of few energy sources that does not release greenhouse gases when it is burned to generate electricity or propel vehicles. But for now almost all hydrogen production releases CO2 (see above)—about one billion metric tons per year worldwide. According to the International Energy Agency (Paris), renewable energy–powered water electrolysis will not be inexpensive enough to make “green” hydrogen affordable until after 2030.

Hydrogen fast facts

CAS Reg. No.	1333-74-0
SciFinder nomenclature	Hydrogen
Empirical formula	H₂
Molar mass	2.02 g/mol
Appearance	Colorless gas
Melting point	-252.8 ºC
Water solubility	1.6 mg/L (1 atm, 20 ºC)

Hydrogen hazard information

Hazard class：Flammable gases, category 1
H220-Extremely flammable gas
Hazard class：Gases under pressure, compressed gas
H280-Contains gas under pressure; may explode if heated

About Molecule of the Week

MOTW has been a popular feature on ACS website since 2001. Many molecules are suggested by our website visitors. Every structure is reviewed by a scientist and displayed in 3-D and flat images with a brief description. Each week’s molecule also links to a sample record from the CAS REGISTRY, which is searched using SciFinder. Each record displays the registry number, index name and synonyms, bibliographic information, and more. Send us a molecule suggestion at motw@acs.org.

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