Group 0 (noble gases) properties and trends

Atomic structure and the periodic table • The periodic table

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Why is radon less commonly used despite fitting Group 0 trends?

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Radon is less commonly used because it is radioactive, which creates safety and handling issues that limit practical applications.

Key concepts

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Full outer electron shells and chemical inertness

Elements in Group 0 have complete outer electron shells: helium has a 1s2 shell and the rest have an ns2 np6 arrangement. A complete outer shell produces electronic stability, which reduces the tendency to gain, lose or share electrons in chemical reactions. This electronic stability causes the group to exist predominantly as uncombined, monatomic gases under standard conditions. Full outer shells also produce high first ionisation energies because removing an electron requires disrupting a stable configuration. The high ionisation energies make electron loss energetically unfavourable, which further reduces chemical reactivity for the group as a whole.

Atomic radius and ionisation energy trends down the group

Atomic radius increases down Group 0 because each successive element has an additional electron shell, which places the outer electrons farther from the nucleus. Increased distance causes weaker electrostatic attraction between nucleus and outer electrons. First ionisation energy decreases down the group because outer electrons sit further from the nucleus and experience greater shielding by inner electrons. Weaker attraction makes it easier, though still energetically costly, to remove an electron compared with lighter group members.

Intermolecular forces, boiling points and density trends

Noble gases are monatomic and nonpolar, so their only significant intermolecular forces are London (dispersion) forces. London forces strengthen with increasing atomic size and electron number because larger electron clouds are more easily distorted (greater polarizability). Stronger London forces cause higher melting and boiling points down the group, so heavier noble gases liquefy and solidify at progressively higher temperatures. Density increases down the group because atomic mass increases faster than atomic volume. Heavier atoms produce denser gases and much higher densities for liquid and solid phases of the heavier noble gases compared with lighter ones.

Limits to inertness and practical exceptions

Noble gas inertness is not absolute. Very heavy noble gases, especially xenon, form stable compounds under specific conditions because high polarizability and available vacant orbitals allow bonding with highly electronegative elements. Reactions with fluorine and oxygen produce xenon fluorides and oxides in controlled laboratory conditions. Radon introduces additional limiting factors. Radon is radioactive, which affects practical handling and chemical study. Relativistic effects on very heavy atoms also modify orbital energies slightly, producing subtle deviations from simple trends for the heaviest noble gases.

Key notes

Important points to keep in mind

Full outer electron shells cause very low chemical reactivity.

Atomic radius increases down the group because of added electron shells.

First ionisation energy decreases down the group due to increased distance and shielding.

London dispersion forces strengthen down the group because polarizability increases with electron count.

Melting and boiling points increase down the group as London forces become stronger.

Density increases down the group as atomic mass rises faster than volume.

Heavier noble gases can form compounds under extreme conditions; xenon compounds are common laboratory examples.

Radon is radioactive, which limits experimental study and practical use.