1869年门捷列夫完成了世界上第一张化学元素周期表，除了把当时所知的全部63种元素按原子量大小分组(族)排列外，还在表中留下一些空位，预言了与硼、铝、硅类似的元素的存在及其性质。随后的20多年内，这些空位相继被新发现的元素填补。1877年中国首任驻英公使郭嵩焘听到了门捷列夫的预言与元素镓的发现这一故事，联想到发现海王星的经过，由衷感叹西方科学的精致与功效。

Mendeleev completed the first periodic table of chemical elements in the world in 1869, including all 63 known elements at that time arranged into different families in accordance with atomic weight. In addition, he reserved some vacancies and predicted
the existence of some unknown elements and their characters. In the following decades, these vacancies had been successively filled up by newfound elements. In 1877, Guo Songtao, the first Chinese envoy to Britain, heard the story about Mendeleev’s prediction and
the discovery of element Gallium, associating with the course of discovery of Neptune, he unfeignedly praised the western sciences in
terms of delicacy and efficacy.