nitrogen：氮（元素）

the chemical element of atomic number 7, a colorless, odorless, unreactive gas that forms about 78 percent of the earth’s atmosphere.

Liquid nitrogen (made by distilling liquid air) boils at 77.4 kelvins (-195.8°C) and it is used as a coolant.

词源：late 18th century: from French nitrogène (see niter, -gen).
niter， “硝石”（见下节）；-gen，表示 produce，generate。

niter: 硝石

niter 是 potassium nitrate（硝酸钾，见下节）的别称。

nitric acid: 硝酸

Nitric acid (HNO₃), also known as aqua fortis (Latin for “strong water”) and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water.

这里 nitric 用作形容词。
词源：late 18th century: from French (acide) nitrique (see niter, -ic).
niter，硝石；-ic，在化学中，denoting an element in a higher valence. 有higher valence，就有lower valence，用 -ite 表示（见后节）

nitrate: n. 硝酸盐; 硝酸根

nitrate is a polyatomic ion with the molecular formula NO₃^-. Organic compounds that contain the nitrate ester as a functional group (R-ONO₂) are also called nitrates. Nitrates are common components of fertilizers and explosives.

词根：late 18th century: from French(see niter, -ate).
niter，硝石；-ate，在化学中，forming nouns denoting a salt or ester， especially of an acid with a corresponding name ending in -ic （关于 -ic 见前节）。

potassium nitrate: 硝酸钾

a white crystalline salt, occurring naturally and produced synthetically, used in fertilizer, as a meat preservative, and as a constituent of gunpowder.

nitrous acid：亚硝酸

这里nitrous用作形容词。-ous 后缀表示 lower valence of an element.

Nitrous acid (molecular formula HNO₂) is a weak and monobasic acid known only in solution, in the gas phase and in the form of nitrite (NO₂^-) salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.

注：monobasic acid：一元酸（只有一个hydrogen ion）；diazonium salts：重氮盐（di- two；azo [=a+zo literally not life] nitrogen；-onium ammonium）

nitrite：n. 亚硝酸盐; 亚硝酸根

a salt or ester of nitrous acid, containing the anion NO₂^- or the group -NO₂.

词源：early 19th century: from niter + -ite.
niter，硝石；-ite，在化学中，forming names of salts or esters of acids ending in -ous （见上节）。

sodium nitrite：亚硝酸钠

Sodium nitrite is an inorganic compound with the chemical formula NaNO₂. It is a white to slightly yellowish crystalline powder that is very soluable in water and is hygroscopic.

注： hygroscopic: (hygro- wet, moisture) (of a substance) tending to absorb moisture from the air 吸湿的

小结

nitrogen是名词，表示化学元素 氮，这个词来自于 niter（硝石）。氮元素可以形成两种酸 nitric acid 和 nitrous acid，中文名称分别是 硝酸 和 亚硝酸。中文可以添加一个字加以区分，但是英文中只能使用不同的后缀来区分：-ic 表示高价酸，-ous 表示低价酸。

在化学反应后，酸可以生成盐，nitric acid生成的盐被称为 nitrate (硝酸盐)，例如：potassium nitrate 硝酸钾；nitrous acid生成的盐被称为 nitrite (亚硝酸盐)，例如：sodium nitrite 亚硝酸钠。

nitric acid —> nitrate (salt)
nitrous acid —> nitrite (salt)

nitrate 和 nitrite 还可以用于表示 “酸根离子”， nitrate表示 硝酸根(NO₃^-)，nitrite表示 亚硝酸根(NO₂^-)。