The noble gases of the far right group of the periodic table are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn). These elements, which are gaseous at room temperature, make up a very small percent of Earth. In addition to being rare, they are also considered inert due to their full outer electron shells, and do not tend to react with other elements. It is due to their rarity and their tendency not to interact with others that they are called noble.
Other elements, such as Hydrogen, do not have full outer electron shells. The atoms of these less noble elements seek to achieve a full outer shell by either gaining, losing, or sharing electrons in chemical bonds with other elements or by pairing up with other atoms from their own element to form diatomic molecules.