化合价的理论大概在十九世纪中期提出,化学键的理论在本世纪初期才提出。关于分子结构的化学键,现在主要有下列几种类型: 在三十年代到四十年代,化学家有不同的看法。例如硝酸的分子结构可表示如(Ⅰ)和(Ⅱ)。有许多理由可以认为硝酸分子中氮氧之间的三个键都 The theory of valence was proposed around the mid-nineteenth century and the theory of chemical bonds was not proposed until the beginning of this century. There are several major types of chemical bonds about the molecular structure nowadays: chemists had different opinions in the 1930s and 1940s. For example, the molecular structure of nitric acid can be represented as (I) and (II). There are many reasons that nitric acid can be thought of as the three bonds between nitrogen and oxygen