Chemistry 6.14-6.16 - Noble gases

Full outer shells and chemical inertness

Group 0 is the far-right column of the periodic table. Its elements include helium, neon, argon, krypton, xenon and radon. They are called the noble gases.

Chemical reactions usually involve the electrons in an atom's outer occupied shell. Atoms with incomplete outer shells may react by losing, gaining or sharing electrons. Noble-gas atoms already have full outer shells, so they have little tendency to lose, gain or share electrons and are therefore chemically inert compared with other elements.

Helium is the important exception to the careless rule that every noble gas has eight outer electrons. It has only one occupied shell, and that first shell is complete with two electrons. A full shell is what matters.

[DIAGRAM: asset_name: Chemistry 6.14-6.16 - Noble gases and inertness - diagram 01; asset_slug: chemistry_6_14_6_16_noble_gases_and_inertness__diagram_01; recommended_method: image_gen; description: A clean monochrome three-panel electron-shell model headed exactly Helium 2, Neon 2.8 and Argon 2.8.8. Show a small labelled nucleus and respectively one, two and three concentric occupied-shell rings. Place exactly 2 filled electron dots on helium's first and outer shell; exactly 2 dots on neon's first shell and 8 on its second and outer shell; exactly 2 dots on argon's first shell, 8 on its second shell and 8 on its third and outer shell. Make each outermost ring slightly heavier and place the exact caption full outer shell beneath each panel. Use #6A6B6E linework, labels and electron dots on white. Exclude bonds, ions, arrows, orbital notation, extra or decorative dots, colour-dependent meaning, gradients and frames.]

At the macroscopic level, a noble gas shows little or no visible chemical change when many other substances would react. At the particle level, each atom keeps its already complete outer shell rather than readily transferring or sharing electrons. The configurations 2, $\mathrm{2.8}$ and $\mathrm{2.8.8}$ are the symbolic evidence used by the GCSE model.

This lesson has no Higher-only content: Chemistry 6.14-6.16 is common to both Foundation and Higher tier on Combined Science Chemistry 2 (1SC0/2CF or 1SC0/2CH).

Properties select the use

A useful explanation does more than name a gas and a job. It links a property of the gas to what that job requires:

property → useful consequence → use

Chemical inertness and non-flammability are related but not identical. Inertness describes very low chemical reactivity in general; non-flammability specifically means that the substance does not burn in oxygen. Low density is a separate physical property and does not mean that helium has no mass.

Neon in a sealed discharge tube provides another useful distinction. Neon remains stable because it is inert, but the reddish-orange light is produced when an electrical discharge excites the gas. Inertness is not itself the cause of the glow.