The discovery of hafnium, element number 72, provided a controversial episode in chemistry. G. Urbain, a French chemist, claimed in 1911 to have isolated an element number 72 from a sample of rare earth (elements 58–71) compounds. However, Niels Bohr believed that hafnium was more likely to be found along with zirconium than with the rare earths. D. Coster and G. von Hevesy, working in Bohr's laboratory in Copenhagen, showed in 1922 that element 72 was present in a sample of Norwegian zircon, an ore of zirconium. (The name hafnium comes from the Latin name for Copenhagen, Hafnia). (a) How would you use electron configuration arguments to justify Bohr's prediction?

Key Concepts

Electron Configuration

Electron configuration describes the distribution of electrons in an atom's orbitals. For elements, this configuration follows the Aufbau principle, Hund's rule, and the Pauli exclusion principle, which dictate how electrons fill available energy levels. Understanding the electron configuration of hafnium and zirconium is crucial, as it reveals their chemical properties and helps explain why hafnium is found alongside zirconium in nature.

Periodic Trends

Periodic trends refer to the predictable patterns in elemental properties that arise from their positions in the periodic table. These trends include atomic radius, ionization energy, and electronegativity. Hafnium and zirconium are in the same group (Group 4), which suggests they share similar chemical behaviors, supporting Bohr's prediction that hafnium would be found with zirconium rather than with the rare earth elements.

Chemical Similarity

Chemical similarity is the concept that elements with similar electron configurations exhibit comparable chemical properties. This is particularly evident in transition metals, where elements in the same group often form similar compounds. Bohr's assertion that hafnium would be found with zirconium is based on their analogous electron configurations, leading to similar reactivity and bonding characteristics, which are essential for understanding their occurrence in nature.