Final answer:
An element's position in the periodic table is determined by its atomic number. Element 115, a synthetic element, was predicted based on trends seen in the periodic table and was officially recognized by IUPAC in 2015.
Step-by-step explanation:
An element's position in the periodic table is defined primarily by its atomic number, which is the number of protons in the nucleus of an atom. This organization method reflects the periodic trends in the properties of the elements. The vertical columns are known as groups, and elements within a group share similar properties. The periodic table also aligns elements into rows called periods. Dmitri Mendeleev initially arranged the elements by atomic masses and left intentional gaps for undiscovered elements. These gaps allowed for the prediction of new elements and their properties based on observed trends.
The existence of element 115 was predicted using these patterns in the periodic table. As discoveries of new elements were made, scientists exploited the idea that heavier elements could be synthesized by fusing lighter atomic nuclei together. These synthetic elements, including element 115, tend to be unstable and exist only briefly, yet their creation and identification have continued to validate the predictive power of Mendeleev's periodic table.
In December 2015, the International Union of Pure and Applied Chemistry (IUPAC) officially recognized the discovery of element 115 alongside elements 113, 117, and 118, and approved their addition to the periodic table. This was the culmination of various experiments that showed evidence of these elements through the collision of lighter nuclei at high speeds.