na指的是多少呢?
na等于23g/mol。
钠是一种金属元素，在周期表中位于第3周期、第ⅠA族，是碱金属元素的代表，质地柔软，能与水反应生成氢氧化钠，放出氢气，化学性质较活泼。钠元素以盐的形式广泛的分布于陆地和海洋中，钠也是人体肌肉组织和神经组织中的重要成分之一。
NA的基本性状：
银白色立方体结构金属。新切面有银白色光泽，在空气中氧化转变为暗灰色。质软而轻，密度比水小，在-20℃时变硬，遇水剧烈反应，生成氢氧化钠和氢气并产生大量热量并使自身熔化，量多时会导致自燃或爆炸。在空气中，燃烧时发亮黄色火焰。
遇乙醇也会反应，跟乙醇的羟基反应，生成氢气和乙醇钠，同时放出热量，反应剧烈程度较水平缓。能与卤素和磷直接化合。
能还原许多氧化物成元素状态，也能还原金属氯化物。溶于液氨时成蓝色溶液。在氨中加热生成氨基钠。溶于汞生成钠汞齐。相对密度(H₂O)0.968。熔点97.82℃。沸点881.4℃。有腐蚀性。CAS号：7440-23-5。
1。 CAS no. (number): 不是危险品而已， 而是所有的化学品都有的一个编号， 便于数据库的查找。
CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers or CAS RNs.
Chemical Abstracts Service (CAS), a division of the American Chemical Society, assigns these identifiers to every chemical that has been described in the literature. The intention is to make database searches more convenient, as chemicals often have many names. Almost all molecule databases today allow searching by CAS number.
As of Nov 2, 2005, there were 26,901,696 substances in the CAS registry — the current number is published here. About 4,000 new numbers are added each day.
CAS registry number is separated by hyphens into three parts, the first consisting of up to 6 digits, the second consisting of two digits, and the third consisting of a single digit serving as a check digit.
2。 UN no. 才是危险品特有的。 运输都要有这号码。
UN numbers or UN IDs are four-digit numbers that identify dangerous goods hazardous substances and articles (such as explosives, flammable liquids, toxic substances, etc.) in the framework of international transport. Some hazardous substances have their own UN numbers (e.g. acrylamide has UN2074), while sometimes groups of chemicals or products with similar properties receive a common UN number (e.g. flammable liquid, not otherwise specified, have UN1993). A chemical in its solid state may receive a different UN number than the liquid phase if their hazardous properties differ significantlysubstances with different levels of purity may also receive different UN numbers.
UN numbers range from UN0001 to about UN3500 and are assigned by the United Nations Committee of Experts on the Transport of Dangerous Goods. They are published as part of their Recommendations on the Transport of Dangerous Goods, also known as the Orange Book. These recommendations are adopted by the regulatory organization responsible for the different modes of transport.
NA numbers (North America), also known as DOT numbers are issued by the United States Department of Transportation and are identical to UN numbers, except that some substances without a UN number may have an NA number. These additional NA numbers use the range NA8000 - NA9999.
Associated with each UN number is a hazard identifier, which encodes the general hazard class and subdivision (and, in the case of explosives, their compatibility group). For instance, the hazard identifier of acrylamide is 6.1 and the one of cigarette lighters is 2.1. If a substances poses several dangers, then subsidiary risk identifiers may be specified. It is not possible to deduce the hazard class(es) of a substance from its UN number: they have to be looked up in a table.
The hazard classes and their divisions are:
Class 1: Explosives
Division 1.1: Substances and articles which have a mass explosion hazard
Division 1.2: Substances and articles which have a projection hazard but not a mass explosion hazard
Division 1.3: Substances and articles which have a fire hazard and either a minor blast hazard or a minor projection hazard or both, but not a mass explosion hazard
Division 1.4: Substances and articles which present no significant hazard
Division 1.5: Very insensitive substances which have a mass explosion hazard
Division 1.6: Extremely insensitive articles which do not have a mass explosion hazard
Class 2: Gases
Division 2.1: Flammable gases
Division 2.2: Non-flammable, non-toxic gases
Division 2.3: Toxic gases
Class 3: Flammable liquids
Class 4: Flammable solidssubstances liable to spontaneous combustionsubstances which, on contact with water, emit flammable gases
Division 4.1: Flammable solids, self-reactive substances and solid desensitised explosives
Division 4.2: Substances liable to spontaneous combustion
Division 4.3: Substances which in contact with water emit flammable gases
Class 5: Oxidizing substances and organic peroxides
Division 5.1: Oxidizing substances
Division 5.2: Organic peroxides
Class 6: Toxic and infectious substances
Division 6.1: Toxic substances
Division 6.2: Infectious substances
Class 7: Radioactive material
Class 8: Corrosive substances
Class 9: Miscellaneous dangerous substances and articles
中文名 钠 英文名 Sodium 化学式 Na 分子量 22.9898 CAS登录号 7440-23-5 熔点 97.72℃ 沸点 883℃ 密度 0.968g/cm³（室温） 外观 银白色有金属光泽固体 离子 Na+ 电子排布式 1s2 2s2 2p6 3s1 危险性 易自燃、遇水放热 管制类型 易制爆
na的意思：是钠（Natrium），是一种金属元素，元素符号是Na，英文名sodium。
在周期表中位于第3周期、第ⅠA族，是碱金属元素的代表，质地柔软，能与水反应生成氢氧化钠，放出氢气，化学性质较活泼。
na的工业用途：
测定有机物中的氯。还原和氢化有机化合物。检验有机物中的氮、硫、氟。去除有机溶剂（苯、烃、醚）中的水分。除去烃中的氧、碘或氢碘酸等杂质。制备钠汞齐、醇化钠、纯氢氧化钠、过氧化钠、氨基钠、合金、钠灯、光电池，制取活泼金属。
