Group 18 Elements — Definition

Definition

Imagine a group of elements so content with their electron arrangements that they rarely, if ever, bother to react with other elements. That's essentially what Group 18 elements, also known as noble gases or inert gases, are.

Located at the far right of the periodic table, they include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn). Their defining characteristic is their extraordinary chemical stability, which means they are very unreactive.

This stability comes from their electronic configuration: all of them, except Helium, have a complete octet of electrons in their outermost shell ($ns^2np^6$). Helium, being the smallest, has a complete duplet ($1s^2$).

This full valence shell makes them highly stable, as they have no strong tendency to gain, lose, or share electrons to achieve a stable configuration – they already possess one.

Because of this inertness, they exist as individual atoms rather than forming molecules, making them monoatomic gases. They have very low melting and boiling points because the only forces of attraction between their atoms are weak London dispersion forces.

As you move down the group from Helium to Radon, their atomic size increases, leading to stronger London dispersion forces and consequently, a gradual increase in their melting and boiling points. Their ionization enthalpies are exceptionally high, meaning it takes a lot of energy to remove an electron, further contributing to their unreactivity.

Conversely, their electron gain enthalpies are positive (or very slightly negative), indicating they have no desire to accept an electron.

Historically, they were considered completely unreactive, hence the term 'inert gases.' However, in the early 1960s, scientists successfully synthesized compounds of Xenon and Krypton, proving that their inertness is not absolute, especially for the heavier members of the group.

This discovery revolutionized our understanding of chemical bonding. Despite this, their primary applications still leverage their inert nature, such as providing inert atmospheres for welding, filling light bulbs, and use in various scientific instruments.

Helium is also crucial in cryogenics and for diluting oxygen in diving tanks.