十九世纪的化学家不久就发现许多化合物是不可能用一种简单的,可以解释所有他们已知反应的公式来阐明一个公式说明了的一种特定反应。而另一个公式则解释另一种不同的反应,一个化学家也许用一种化合物的四种或五种不同的分子模型就可以说明那种化合物的所有已知的反应,但这种方法只是增加困难:常识向化学家们表明,任何物质应该 Nineteenth-century chemists soon discovered that many compounds make it impossible to elucidate a particular reaction described by a formula using a simple formula that explains all their known reactions. While the other formula explains a different reaction. A chemist might describe all the known reactions of that compound with four or five different molecular models of one compound, but this method only adds Difficulties: Common sense shows to chemists that anything should