In the early 20th century English physicist Henry Moseley speculated that within the nucleus laid the answer to the question of how many elements were present.
Moseley developed a unique way of studying atoms which scientists still use a different technique of today. He used a X-ray spectra. He found out that every element had it's own unique energy signature .
Interesting... I wonder if these energy signatures relate to the number of protons. I guess there's only one way to find out.
He became the first person, to measure the number of protons in the nucleus of an element, now known as the atomic number. Atomic numbers are whole numbers, and cannot have decimals. Thus, Moseley realized that the atomic number, not the atomic mass determines the number and order of the elements, and that became the trend that the periodic table would follow.
Moseley was just 26 when he completed his research. However at the outbreak of World War 1 he participated, and was unfortunately shot through the head by a sniper.
In view of what he might still have accomplished...
His death may well have been the single most costliest death of the war to mankind.
The periodic table, one of the greatest foundations of mankind is so awe inspiring because of how so many individuals from chemistry and physics backgrounds provided research and knowledge that all pieced together as one table. The changes in the role of scientific practices from models to theories to arguments highlight how knowledge progressed over time due to advanced apparatus. From Berzelius's glassblowing techniques to the spectroscope of Kirchhoff, and to the X-ray spectra. They have all helped organize the elements into the famous periodic table.