Final answer:
Noble gases like helium and neon are unreactive due to their full outer electron shells, which follow the octet rule, making them stable and preventing them from readily participating in chemical reactions. This makes them useful in applications requiring inert conditions, such as in light bulbs and for welding.
Step-by-step explanation:
The noble gases, which include elements such as helium, neon, argon, krypton, xenon, and radon, are found in group 18 of the periodic table. These elements are highly unreactive because they have a complete outer shell of electrons, typically with an electron configuration that ends in s²p¶.
The stability of their electron configuration means that noble gases have very high ionization energies and do not easily gain or lose electrons to form compounds. Most chemical reactions involve the sharing or transferring of electrons, but the noble gases' filled outer shells mean that they rarely participate in such reactions under normal conditions.