1839.948ArArgon
Argon (Ar) — element 18noble gas · group 18, period 3
Argon is a chemical element with the symbol Ar and atomic number 18. It is a noble gas in group 18, period 3 of the periodic table (the p-block), with a standard atomic mass of 39.948 u. At room temperature (25 °C) argon is a gas.
💡 Known for: The third most abundant gas in air (about 0.93%); used as an inert shielding gas for welding and inside light bulbs.
# Argon properties
| Symbol | Ar |
|---|---|
| Atomic number | 18 |
| Atomic mass | 39.948 u |
| Category | noble gas |
| Group | 18 |
| Period | 3 |
| Block | p-block |
| Electron configuration | [Ne] 3s² 3p⁶ |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ |
| Electrons per shell | 2, 8, 8 |
| Protons / electrons | 18 / 18 |
| State at 25 °C | gas |
| Melting point | 83.8 K (-189.3 °C, -308.8 °F) |
| Boiling point | 87.3 K (-185.8 °C, -302.5 °F) |
| Density | 1.784 g/L |
| Electronegativity (Pauling) | — |
| First ionization energy | 15.76 eV |
| Atomic radius | 71 pm |
| Discovered | 1894 |
# Electron configuration of argon
The electron configuration of argon is [Ne] 3s² 3p⁶, written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶. Its 18 electrons fill 3 shells as 2, 8, 8, so the outermost shell holds 8 electrons. As a group 18 element, argon has 8 valence electrons.
# Related elements
ClChlorineprevious elementKPotassiumnext elementHeHeliumgroup 18NeNeongroup 18KrKryptongroup 18XeXenongroup 18RnRadongroup 18OgOganessongroup 18
# Argon FAQ
What is the atomic number of argon?
The atomic number of argon is 18: every argon atom has 18 protons in its nucleus. Its symbol is Ar.
What is the atomic mass of argon?
The standard atomic mass of argon is 39.948 u.
What is the electron configuration of argon?
Argon's electron configuration is [Ne] 3s² 3p⁶ (1s² 2s² 2p⁶ 3s² 3p⁶), with 2, 8, 8 electrons per shell.
Is argon a metal?
No. Argon is a noble gas, a nonmetal.
What is the melting point of argon?
Argon melts at 83.8 K (-189.3 °C, -308.8 °F) and boils at 87.3 K (-185.8 °C, -302.5 °F).
What is argon used for / known for?
The third most abundant gas in air (about 0.93%); used as an inert shielding gas for welding and inside light bulbs.