A third is certain basic chemicals such as carbon, oxygen and nitrogen.
第三种是某些基本的化学物质,如碳、氧和氮。
A century earlier, Henry Cavendish had noted the existence of a residual gas when oxygen and nitrogen are removed from air, but its importance had not been realized.
一个世纪前,亨利·卡文迪什注意到当空气中的氧气和氮气被除去,还有其他剩余气体存在,但人们还没有认识到它们的重要性。
But improved farming methods later increased their yields and, at the same time, made better use of chemical nitrogen fertilizer.
VOA: special.2009.07.28
So in terms of the first step of skeletal structure, this is actually going to be easier because we don't have a central atom, we just have carbon and nitrogen here.
对于第一步画出骨架,其实比刚才更容易,因为我们没有一个中心原子,我们这里只有碳和氮两个原子。
For example, we can talk about nitrogen, and nitrogen has five valence electrons shown here.
例如,我们可以讨论氮原子,氮原子有5个价电子。
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