MCQ Detailed View

In the periodic table, most elements combine with identical atoms to form diatomic or polyatomic molecules. For example, hydrogen exists as H₂, oxygen as O₂, and nitrogen as N₂. However, one group of elements is unique because its members exist naturally as single atoms. These are the noble gases found in Group 18 of the periodic table.

Group 18 elements include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These gases are chemically stable due to their completely filled valence electron shells. Helium has two electrons, while the others have eight electrons in their outermost shell. This complete configuration gives them maximum stability, meaning they have little tendency to gain, lose, or share electrons. As a result, they do not form molecules and remain as individual atoms.

This property is described as existing in the monoatomic state. Monoatomic gases are composed of single atoms that are not bonded to each other. In contrast, elements from other groups usually bond with their own kind to achieve stability. For example, halogens (Group 17) form diatomic molecules like Cl₂ or F₂ to complete their octets. Alkali metals (Group 1) exist as metallic solids, and nonmetals such as sulfur (Group 16) exist as S₈ molecules.

The noble gases, because of their inertness, are sometimes called inert gases. They are colorless, odorless, and tasteless under standard conditions. Their lack of reactivity makes them useful in applications such as lighting (neon lamps, argon in bulbs), welding (helium and argon), and as protective environments in chemical processes.

Thus, the only group in the periodic table where elements naturally exist as monoatomic molecules is Group 18, the noble gases.