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18Ar39.948
Noble Gasesgas at STPP-block

Argon

Group: 18•Period: 3•Standard Atomic Weight: 39.948 u
Open Full Periodic TableView Bohr Model

Why is Argon in this position?

Understanding the scientific rationale behind Argon's position in the periodic table:

Group Assignment
Group 18

Belongs to Group 18 because it has a completely filled octet of 8 valence electrons (3s² 3p⁶).

Period Assignment
Period 3

Belongs to Period 3 because its valence electrons fill the n=3 shell.

Orbital Block
P-block

Belongs to the p-block because its valence subshell is a full 3p orbital.

Chemical Category
Noble Gases

Classified as a noble gas due to its complete chemical inertness and zero reactivity under standard ambient conditions.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 8]

Bohr Atomic Shell Model(2, 8, 8)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

18 Protons (p⁺)22 Neutrons (n⁰)
KShell K: Electron 1 of 2Shell K: Electron 2 of 2LShell L: Electron 1 of 8Shell L: Electron 2 of 8Shell L: Electron 3 of 8Shell L: Electron 4 of 8Shell L: Electron 5 of 8Shell L: Electron 6 of 8Shell L: Electron 7 of 8Shell L: Electron 8 of 8MShell M: Electron 1 of 8Shell M: Electron 2 of 8Shell M: Electron 3 of 8Shell M: Electron 4 of 8Shell M: Electron 5 of 8Shell M: Electron 6 of 8Shell M: Electron 7 of 8Shell M: Electron 8 of 8ArZ = 18

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):2 / 2 electrons (100%)
Shell L (n=2):8 / 8 electrons (100%)
Shell M (n=3):8 / 18 electrons (44%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶

Neutral ground state configuration. Valence electrons: 8.

Atomic & Quantum Properties

Electronegativity (Pauling)Not available
1st Ionization Energy1520.6 kJ/mol
Electron Affinity0 kJ/mol
Atomic Radius (empirical)71 pm
Common Oxidation States0
Crystal StructureFCC

Physical & Thermal Properties

Density at STP0.00178 g/cm³
Melting Point-189.35 °C (83.8 K)
Boiling Point-185.85 °C (87.3 K)
Magnetic OrderingDiamagnetic
Discovery Year1894
Discovered ByLord Rayleigh & Sir William Ramsay

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Inert shielding gas for TIG and MIG welding of titanium and aluminium
  • Filling gas for double-pane insulated windows to reduce thermal heat transfer
  • Protective atmosphere for growing silicon and germanium semiconductor crystals
  • Gas filling for incandescent and fluorescent light bulbs to preserve filaments
Occurrence in Nature

Makes up 0.93% of Earth's atmosphere by volume, produced continuously by radioactive decay of Potassium-40 in Earth's crust.

Etymology & Name Origin

From Greek 'argos' meaning lazy or inactive

Important Chemical Compounds
HArF (Argon fluorohydride, stable only at cryogenic temperatures below 40 K)
Interesting Chemical Facts
  • • Argon is significantly more abundant in Earth's atmosphere than carbon dioxide, water vapor, and methane.
  • • The Argon-40 / Potassium-40 radiometric clock is used by geologists to date ancient volcanic rocks millions of years old.
  • • Lord Rayleigh and William Ramsay were awarded the 1904 Nobel Prizes in Physics and Chemistry respectively for discovering argon.
Safety & Handling Note

Chemically inert and non-toxic, but denser than air and can accumulate in low-lying confined spaces causing silent asphyxiation.

Explore Neighborhood Elements

Same Group (Group 18):
#2He#10Ne#36Kr#54Xe#86Rn#118Og
Same Period (Period 3):
#11Na#12Mg#13Al#14Si#15P#16S#17Cl