Periodic Table/Argon

← ClK →

18Ar39.9480 Da

Argon

Noble Gas·Period 3, Group 18·p-block

Monatomic noble gas. Makes up 0.93% of the air. Colourless, odorless. Is inert and has no true compounds. Lord Rayleigh and Sir william Ramsey identified argon in 1894.

Gallery

Vial of glowing ultrapure argon. Original size in cm: 1 x 5

Jurii, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/argon.php

Emission spectrum

Physical Propertiesmass · density · phase · crystal

Atomic Mass

39.9480Da

Density

0.0016g/L

Phase (STP)

Gas

Melting Point

83.8K

Boiling Point

87.3K

Molar Heat

0.5200J/(mol·K)

Crystal Structure

FCC

Lattice Constant

5.260Å

Atomic Radiiatomic · covalent · van der Waals

Atomic (Empirical)

71.00pm

Covalent

96.00pm

Van der Waals

188.00pm

Electronic Propertieselectronegativity · ionization · affinity

Electron Configuration

[Ne] 3s2 3p6

Electron Shells

2, 8, 8

Electronegativity

—

Electron Affinity

-11.5kJ/mol

1st Ionization Energy

15.8kJ/mol

Oxidation States

Orbital DiagramAufbau · Hund's rule · Pauli exclusion

↑↓

1s²

↑↓

2s²

↑↓

2p⁶

↑↓

3s²

↑↓

3p⁶

Full: 1s2 2s2 2p6 3s2 3p6Short: [Ne] 3s2 3p6

Ionization Energies (18 known)

Emission Spectrumvisible range · characteristic spectral lines

697

707

738

416

420

Ar emission

380nm750nm

696.5 nm(100%)706.7 nm(70%)750.4 nm(50%)738.4 nm(50%)415.9 nm(30%)420.1 nm(30%)

Abundanceby mass

🌍Earth's Crust

3.5 ppm

🌊Ocean

450.0 ppb

✨Universe

77.0 ppm

🧬Human Body—

Log scale · ppm = parts per million by mass

Biological Role

No biological role

Inert noble gas with no biological role.

Discovery

Discovered By

Sir William Ramsey, Baron Rayleigh

Named By

—

Year

1894

Nuclear Data

Known Isotopes

Stable Isotopes

Stable Mass Numbers

29, 36, 38, 40

Natural isotopic abundance (IUPAC recommended values)

Isotopes of Ar26 known

Nuclide	Z	N	Mass (AMU)	Half-life	Decay	Jπ	Abundance
²⁹Arstable	18	11	29.040761	Stable	2p (1%)	5/2+	—
³⁰Ar	18	12	30.023694	Unknown	2p (1%)	0+	—
³¹Ar	18	13	31.012158	15.0 ms	β⁺ (1%), β⁺p (0.6829999999999999%), 2p (0.09%), B+pA (0.0038%), 3p (0.0007000000000000001%), β⁺α (0.0003%), 2p (0.000005999999999999999%)	5/2+	—
³⁶Arstable	18	18	35.967545	Stable	2β⁺	0+	33.3600%
³⁸Arstable	18	20	37.962732	Stable	stable (1%)	0+	6.2900%
⁴⁰Arstable	18	22	39.962383	Stable	stable (1%)	0+	9960.3500%
⁵²Ar	18	34	51.998519	Unknown	β⁻, β⁻n, 2n	0+	—
⁵³Ar	18	35	53.007290	Unknown	β⁻, β⁻n, 2n	5/2-	—
⁵⁴Ar	18	36	54.013484	Unknown	β⁻, β⁻n, 2n	0+	—

Click any isotope for its full page with decay chain:

²⁹Ar ³⁰Ar ³¹Ar ³²Ar ³³Ar ³⁴Ar ³⁵Ar ³⁶Ar ³⁷Ar ³⁸Ar ³⁹Ar ⁴⁰Ar ⁴¹Ar ⁴²Ar ⁴³Ar ⁴⁴Ar ⁴⁵Ar ⁴⁶Ar ⁴⁷Ar ⁴⁸Ar ⁴⁹Ar ⁵⁰Ar ⁵¹Ar ⁵²Ar ⁵³Ar ⁵⁴Ar

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