Dmitri Mendeleev, the creator of the periodic table, made several remarkable predictions about the existence and properties of undiscovered elements. While it is true that Mendeleev predicted the existence of Gallium and estimated its density, it is important to note that he did not possess detailed knowledge of the crystal structure of the element at that time.
Mendeleev's prediction of density was based on the patterns and trends he observed in the known elements and their properties. He noticed that elements with similar chemical behavior tended to have similar densities. By examining the properties of neighboring elements in the periodic table, Mendeleev made an educated guess about the density of the missing element.
In the case of Gallium, Mendeleev correctly predicted its existence and estimated its density to be 5.9 grams per cubic centimeter (g/cm³). However, Gallium's actual density is approximately 5.91 g/cm³, which is remarkably close to his prediction.
It is worth mentioning that density is influenced by various factors, including atomic mass, atomic radius, and packing arrangement in the crystal lattice. While crystal structure plays a significant role in determining density, Mendeleev's prediction was based on the assumption that the undiscovered element would fit into the existing periodic trends and exhibit properties similar to its neighboring elements.
Therefore, while the crystal structure is a crucial factor in determining density accurately, Mendeleev's prediction of density was a result of his remarkable understanding of the periodic table and the trends in elemental properties, rather than specific knowledge of the crystal structure of Gallium.