Question

Position of the elements in the periodic elements......

Can there be an element with atomic mass 53 or 54 in between the two elements, chromium \[_{24}^{52}\text{Cr and manganese} \phantom{.} _{25}^{55}\text{Mn}\]?

Answer 1

In Mendeleev's periodic table, elements were arranged by atomic mass, which did not increase by a fixed or predictable amount between consecutive elements. For example, Chromium (⁵²Cr) and Manganese (⁵⁵Mn) show a mass difference of three units.

Henry Moseley resolved this unpredictability by discovering atomic numbers, which always increase sequentially by exactly one unit from one element to the next. Because the atomic number goes directly from 24 Chromium, \[_{24}^{52}\text{Cr to 25 manganese} \phantom{.} _{25}^{55}\text{Mn}\], it confirms that no undiscovered elements with atomic masses of 53 or 54 exist between them.