What is the most unreactive group on the periodic table?
What is the most unreactive group on the periodic table? The most unreactive group on the periodic table is group 18, the noble gases (the least reactive family): helium, neon, argon, krypton, xenon, radon and oganesson.
Their atoms have a full outer electron shell (two electrons for helium, eight for the rest), so they have almost no tendency to gain, lose or share electrons and rarely form compounds, which is why the first six exist as single-atom, colorless, odorless gases (also called inert gases) at room temperature, while oganesson is synthetic and radioactive. This stability is why argon fills light bulbs and welding shields, helium fills balloons and cooling systems, and neon lights glow in signs. If you are studying, you may also want the answer to “what are elements”.
The noble gases are not completely inert: Neil Bartlett made the first noble gas compound, a xenon platinum fluoride, in 1962, and compounds of krypton, xenon and radon now exist, usually with fluorine or oxygen. Helium and neon form no known compounds under ordinary conditions. The same series of answers also covers “where is atomic mass on the periodic table”.
By contrast, the most reactive groups are the alkali metals (group 1) and the halogens (group 17). The reason is electron structure. For a different question, see “where are the metalloids located in the periodic table”.
A full outer shell has no need to take or give electrons, and the noble gases have the highest ionization energies in their periods and very low electron affinities, so they hold on to their electrons firmly. Their boiling points are extremely low (helium boils at about −269 °C, the lowest of any element), and they are monatomic gases, so they do not form molecules like oxygen (O2) or nitrogen (N2). Argon makes up about 0.93 percent of the air and is the third most abundant gas in the atmosphere.
Radon is radioactive and is a health hazard in some homes. The reactivity of other groups goes the other way: alkali metals become more reactive down the group, with cesium and francium the most reactive metals, and halogens become less reactive down the group, with fluorine the most reactive nonmetal. In general, the reactivity of metals increases down a group, while the noble gas family stays the least reactive.