Limitations of Mendeléev’s Classification Electronic configuration of hydrogen resembles that of alkali metals. Like alkali metals, hydrogen combines with halogens, oxygen and sulphur to form compounds having similar formulae, as shown in the examples here. On the other hand, just like halogens, hydrogen also exists as diatomic molecules and it combines with metals and non-metals…

Achievements of Mendeléev’s Periodic Table While developing the Periodic Table, there were a few instances where Mendeleev had to place an element with a slightly greater atomic mass before an element with a slightly lower atomic mass. The sequence was inverted so that elements with similar properties could be grouped together. For example, cobalt (atomic…