Mendeleev was able to predict a number of hitherto unknown elements by using his periodic system. He was able to argue and demonstrate that his periodic table was more complete than the other attempts by his contemporaries.
“The notion that scientific theories are accepted primarily if they make successful predictions seems to be rather well ingrained into scientific culture, and the history of the periodic table has been one of the episodes through which this notion has been propagated.” (p159)
However, in this case, the case of Mendeleev, whilst his periodic table has subsequently been proven as the most effective ordering of the elements to date, his predictions have not all worked out. At best, around half of them have proved to be correct. Why then are his successful predictions used to bolster the validity of his system, whilst his unsuccessful predictions have not been used to refute it? This provides a topic for debate and further investigation as to the validity of Popper’s scientific method. There seems to be a conflict of methodology and scientific process here. The question would be: “To what extent is prediction the single most important factor in determining the validity of a new scientific idea.”
Perhaps the Periodic Table demonstrates a different phenomena to prediction. The periodic table was valid and useful for accommodation. It explained and organised already known facts, and was elegant and robust enough to withstand future discoveries (which were out of Mendeleev’s control). Therefore, Mendeleev’s own failures in prediction do not conflict with the tables ability to organise and explain scientific data. In this light, could the periodic table not be seen then as an administrative system, rather than new science. A new way to order already understood science? This point would need to discuss the extent to which the focus on Atomic Weight can be thought of as a new theory, as opposed to a new ordering system.
“The historian Stephen Brush has coined the apt phrase “contrapredictions” to describe the correction of already known elements.” (p159)
One of Mendeleev’s primary activities was the correction of atomic weight values. His genius can be described as his ability to sift through the entire history of correct and incorrect data, cleaning it up and perceiving intuitively where the faults lay. Regarding Mendeleev’s placement of elements in the periodic system:
“Mendeleev considered a number of criteria in addition to atomic weight ordering, such as family resemblance among elements and the concept of the single occupancy of elements in any space in the periodic table.” (p125)
“The strictest criterion Mendeleev employed was that of the ordering of elements according to increasing atomic weight.” (p125)