Hydrogen is the alphabetically first gas on the periodic table. It has a high closeness of 10, meaning it is strongly associated with the topic of gases. Hydrogen’s isotopes include protium, deuterium, and tritium. Helium, another gas with high closeness (9), also plays a significant role. Noble gases, such as argon, have a general high closeness of 8. The Bohr model of the atom and the periodic table also exhibit closeness of 8. Finally, the concept of the hydrogen economy has a high closeness of 9.
