Dirac–Fock one-centre calculations show (114)H₄ to resemble PbH₄

Abstract

RELATIVISTIC effects have a considerable influence on the chemical behaviour of the heavier elements. Our Dirac–Fock one-centre expansion calculations^1–3 indicate that the X–H bond lengths, R_e, suffer a relativistic contraction of about 5% for PbH₄ (ref. 1) or AuH (ref. 2) and 7% for TlH (ref. 3). If the relativistic effects are included, however, these R_e values mostly agree with experiment to within 2–3%. Relativistic effects also seem to be the main cause of the chemical difference between silver and gold² and, possibly, of the dominant monovalency of thallium³. A relativistic treatment becomes imperative to predict the chemical behaviour of the superheavy elements. Following evidence for primordial superheavy elements⁴, we present here results for the tetrahydride of the element 114 or eka-lead. We believe that such a calculation gives a reasonable estimate for the covalent radius of this element. Although the dominant valency of 114 is expected to be 2, some tetravalent compounds are also expected to be stable⁷. As the latter valency is more convenient for calculations, having closed shells, we here consider (114)H₄.