In the modern periodic table, how are the elements arranged?
Each element has its own unique atomic number, which is the number of protons in the nuclei of its atoms, and which defines the element.
All periods begin with an alkali metal in group 1 and end with a noble gas in group 18/8A.
British scientist Henry Mosely determined the atomic numbers of the known elements and predicted several other elements and where they would go. He was a brilliant scientist, full of promise and most likely on the way to a Nobel Prize. However, when World War I started, Moseley volunteered for the Royal Engineers and was killed.
Isaac Asimov wrote, "In view of what he [Moseley] might still have accomplished … his death might well have been the most costly single death of the War to mankind generally."
"Because of Moseley's death in World War I, and after much lobbying by Ernest Rutherford, the British government instituted a policy of no longer allowing its prominent and promising scientists to enlist for combat duty in the armed forces of the Crown."