One of the chemical controversies of the nineteenth century concerned the element beryllium (Be). Berzelius originally claimed

Question:

One of the chemical controversies of the nineteenth century concerned the element beryllium (Be). Berzelius originally claimed that beryllium was a trivalent element (forming Be³⁺ ions) and that it formed an oxide with the formula Be₂O₃. This assumption resulted in a calculated atomic mass of 13.5 for beryllium. In formulating his periodic table, Mendeleev proposed that beryllium was divalent (forming Be²⁺ ions) and that it gave an oxide with the formula BeO. This assumption gives an atomic mass of 9.0. In 1894 A. Combes (Comptes Rendes, 1894, p. 1221) reacted beryllium with the anion C₅H₇O₂^- and measured the density of the gaseous product. Combes’s data for two different experiments are as follows:

If beryllium is a divalent metal, the molecular formula of the product will be Be(C₅H₇O₂)₂; if it is trivalent, the formula will be Be(C₅H₇O₂)₃. Show how Combes’s data help to confirm that beryllium is a divalent metal.