The elements in Group 18 on the periodic table are called the noble gases. This is because it was originally believed that these elements could not react with other elements to form bonds. The elements in this group are argon, helium, neon, krypton, xenon and radon.
In 1875, Henry Cavendish became the first to classify these elements as noble gases. All the noble gases, with the exception of helium, have eight electrons in their outermost shells. This makes these elements very stable and unlikely to form chemical bonds with other elements. However, they can form bonds to produce compounds. For example, xenon can react with oxygen to form xenon tetroxide.