The lanthanide elements from lanthanum to lutetium inclusive are incorporated into the body of the periodic table. They are subdivided into three sub-groups according to their important oxidation states: La to Sm, Eu to Tm, Yb and Lu, so that Eu and Yb fall directly below Ba; La, Gd, Lu form a column directly below Y; Ce and Tb fall in a vertical line between Zr and Hf. Pm falls below Tc; both are radioactive, and not naturally occurring. The elements (...) with easily attained 2+ and 4+ oxidation states are grouped and clearly differentiated. Gadolinium has an important position as the centre of four triads in the block of elements that surround it– La, Gd, Lu; Ba, Gd, Hf; Eu, Gd, Tb; Yb, Gd, Ce. This new arrangement has the advantages of compactness, simplicity and clarity – there are no tie lines; and important oxidation states of these metals are emphasized. The actinides are also accommodated within this system, and element 114 falls naturally below lead in Group 14. (shrink)

Dmitrii Mendeleev’s periodic system is known for its predictive accuracy, but talk of its completeness is rarer. This is surprising because completeness was a quality that Mendeleev saw as important for a systematization of the chemical elements. Here, I explain how Mendeleev’s valuing of completeness influenced the development of his periodic system. After introducing five indicators of its completeness, I zoom into one in particular: Mendeleev’s inclusion of a schematic row of oxides. I then show how it guided Mendeleev’s predictions (...) of indium and ekaboron, which suggests that the valuing of completeness was instrumental for making predictions. (shrink)

Much has been said about the accuracy of the famous predictions of the Russian chemist Dmitrii Ivanovich Mendeleev, but far less has been written on how he made his predictions. Here we offer an explanation on how Mendeleev used his periodic system to predict both physical and chemical properties of little-known and entirely unknown chemical elements. We argue that there seems to be compelling evidence in favour of Mendeleev genuinely relying on his periodic system in the course of issuing his (...) predictions—a point recently contested by Woody Science after the practice turn in the philosophy, history, and social studies of science, Routledge, Abington, 2014). In particular, by using the known properties of a number of near neighbours of the three entirely unknown elements, we seek to show how the very format of his table enabled it to function as a powerful tool for Mendeleev in arriving at his predicted values. We suggest that Mendeleev’s use of the periodic system in making his prediction gives an illuminative example of what Woody calls “theoretical practices” in science. (shrink)

The theme surrounding scientific discoveries is quite neglected in and about the sciences, especially in terms of historical and epistemological understanding. Discoveries are often treated as simple information about dates, places, and people. This work presents discussions centered on historical episodes related to chemical elements and the Periodic Law, based on reflections by Thomas Kuhn and Norwood Hanson, aiming to highlight and contextualize specific scientific discoveries' conceptual and epistemological structure. With that in mind, issues related to the inseparability of the (...) contexts of discovery and justification are recovered, along with the complex intrinsic structures of the genesis of scientific knowledge and distinct types and categories of scientific discoveries. (shrink)

Several attempts have recently been made to point to ‘the proper place’ for hydrogen in the Periodic Table of the elements. There are altogether five different types of arguments that lead to the following conclusions: hydrogen should be placed in group 1, above lithium; hydrogen should be placed in group 17, above fluorine; hydrogen is to be placed in group 14, above carbon; hydrogen should be positioned above both lithium and fluorine and hydrogen should be treated as a stand-alone element, (...) in the center of the Periodic Table. Although all proposals are based on arguments, not all of them sound equally convincing. An attempt is made, after critical reexamination of the arguments offered, to hopefully point to the best possible choice for the position of hydrogen. A few words are also mentioned on the structure of the Periodic Table and the attempts to reorganize it. (shrink)

This article focuses on the Russian chemist Dmitri Ivanovich Mendeleev's assessment of certain representations of various aspects of the periodic system that employed more mathematical methodology. The equations of interest were created by E. J. Mills, B. N. Chicherin, and J. H. Vincent. The English chemist Mills tried to find a firmer numerical basis for the periodicity of the elements. The Russian lawyer and political philosopher Chicherin was convinced of the existence of a mathematical law underlying the periodic system. The (...) English physicist Vincent explored the connection between atomic weights and the elements' order in listings based on atomic weights—a project which he associated with the periodic system of elements. Although, for Mendeleev, the equations of Mills, Chicherin, and Vincent promised a more precise expression of the law of periodicity, he continued to invoke his earlier standards. In particular, Mendeleev wanted the equations to respect the individuality of the elements, and called for completeness in conveying the complexities of chemical phenomena. Thus, the very qualities that he had valued while developing his periodic system in 1869–1871 also characterised his evaluation of the new means of representing aspects of that system. (shrink)