“…In the somewhat extensive literature sources that were available to us, there are those devoted to the discovery of the PT [1,6,8,11,26,36], its reception [8], the contribution of physics to the periodic law [4,27], the definitions of the term element [10,11,15,20,25,28] and jubilees (centennial) of the death of Mendeleev [17]. The definition of element is in, a way, dual: it relies on a concept of element as an observable (elemental, or simple substance), but also on a concept of element as "a 'basic substance,' something that can survive chemical change and is the common component of different compound substances."…”