Inert gases (noble gases) are placed in Group Zero (also called Group 18 in modern IUPAC notation) because their valency is zero. They have completely filled outermost electron shells (2 electrons in helium, 8 electrons in all others), making them chemically unreactive. Since they neither gain, lose, nor share electrons under normal conditions, their combining capacity (valency) is zero — hence Group Zero.
Noble gases are placed in Group Zero because their valency is zero.
They have completely filled outermost electron shells (octet rule).
He has 2 electrons (full K shell); all others have 8 valence electrons.
Zero valency means they neither gain, lose, nor share electrons.
Noble gases: He, Ne, Ar, Kr, Xe, Rn — in Group 18 (modern) or Group 0 (older).
They are monoatomic gases — exist as single atoms.
Some xenon compounds (XeF₂, XeF₄) exist but are exceptions.
They are non-flammable and chemically inert — used in industrial applications.
In the older periodic table classification, groups were numbered based on valency: • Group 1 elements have valency 1 (e.g., Na, K) • Group 2 elements have valency 2 (e.g., Mg, Ca) • Group 7 elements have valency 1 (e.g., Cl, F) • Group 0 elements have valency 0 (noble gases)
Valency is the combining capacity of an atom. Since noble gases have completely filled electron shells, they have no tendency to: • Lose electrons (unlike metals) • Gain electrons (unlike non-metals) • Share electrons (unlike carbon, nitrogen, etc.)
With zero combining capacity → Valency = 0 → Placed in Group 0.
Noble gas electronic configurations:
• Helium (He) — 2 (completely filled K shell — only 2 electrons needed) • Neon (Ne) — 2, 8 (completely filled K and L shells) • Argon (Ar) — 2, 8, 8 (completely filled K, L, and M shells) • Krypton (Kr) — 2, 8, 18, 8 • Xenon (Xe) — 2, 8, 18, 18, 8 • Radon (Rn) — 2, 8, 18, 32, 18, 8
All have a full outermost shell (octet), which is the most stable electron configuration. This stability is why they do not react — there is no energetic advantage to gaining, losing, or sharing electrons.
In the modern IUPAC periodic table: • Noble gases are placed in Group 18 (rightmost column) • They are in Periods 1 through 6 • Also called Group 0 (older notation) or Group VIII A (some older systems)
Elements and their positions: • He — Period 1, Group 18 • Ne — Period 2, Group 18 • Ar — Period 3, Group 18 • Kr — Period 4, Group 18 • Xe — Period 5, Group 18 • Rn — Period 6, Group 18
Note: Some xenon compounds (XeF₂, XeF₄, XeO₃) exist under extreme conditions, but these are exceptions. For most practical purposes, noble gas valency = 0.
Uses: • He — in balloons, airships, MRI cooling • Ne — in neon signs • Ar — in light bulbs (inert atmosphere) • Kr — in fluorescent lamps • Xe — in camera flash bulbs, anaesthesia • Rn — radioactive, used in cancer radiotherapy
Inert gases are placed in Group Zero because their valency (combining capacity) is zero. They have completely filled outermost electron shells — 2 electrons in helium and 8 electrons in all other noble gases — making them chemically unreactive. Since they do not gain, lose, or share electrons, their valency is 0.
He: 2; Ne: 2,8; Ar: 2,8,8; Kr: 2,8,18,8; Xe: 2,8,18,18,8. All noble gases except helium have 8 electrons in their outermost shell (complete octet), making them extremely stable.
Noble gases are chemically inert because they have completely filled electron shells. A full outermost shell is the most stable configuration. There is no energetic advantage to gaining, losing, or sharing electrons, so they do not react under normal conditions.
They refer to the same group — the noble gases. Group 0 is the older naming convention used when periodic table groups were numbered based on valency. Group 18 is the modern IUPAC notation. Both contain He, Ne, Ar, Kr, Xe, and Rn.
Under extreme conditions, some noble gases can form compounds. Xenon is the most reactive noble gas — XeF₂, XeF₄, XeF₆, and XeO₃ have been prepared. However, for most purposes, noble gas valency is considered zero and they are chemically inert.
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