Argon (Ar)
Noble gas
Argon is the third most abundant gas in Earth's atmosphere — almost 1% of every breath — yet most people have never heard of it. Its total unreactivity makes it the standard “do nothing” gas of industry.
Position on the periodic table
Atomic properties
| Atomic number | 18 |
|---|---|
| Atomic mass | 39.9481 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 |
| Noble gas shorthand | [Ne] 3s2 3p6 |
| Electrons per shell | 2, 8, 8 |
| Valence electrons (outer shell) | 8 |
| Common oxidation states | None common |
| Electronegativity (Pauling) | Not available |
| Covalent radius (approx.) | 106 pm |
| First ionization energy | 1521 kJ/mol |
| Electron affinity | -96 kJ/mol |
Physical properties
| State at 25 °C | Gas |
|---|---|
| Density | 1.784 g/L |
| Melting point | -189.34 °C (83.81 K) |
| Boiling point | -185.85 °C (87.3 K) |
| Appearance | colorless gas exhibiting a lilac/violet glow when placed in a high voltage electric field |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of argon
Argon's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6, usually shortened to [Ne] 3s2 3p6. Its electrons occupy 3 shells (2, 8, 8), placing it in period 3 of the p-block. The 8 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of argon
- Shield gas for welding
- Filling incandescent and fluorescent bulbs
- Insulating layer in double-glazed windows
- Protecting old documents and wine from oxygen
Biological role: None — completely inert.
Occurrence: 0.93% of the atmosphere, produced over geological time by the decay of potassium-40.
History and discovery
Discovered: 1894 — Lord Rayleigh. Name origin: From Greek argos, meaning lazy or inactive.
Discovered in 1894 by Lord Rayleigh and William Ramsay — the first noble gas found on Earth.
Safety notes
Non-toxic but heavier than air — it can pool in low, enclosed spaces and displace oxygen.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Argon
1. What is the chemical symbol of Argon?
2. What is the atomic number of Argon?
3. Which category does Argon belong to?
4. What is the state of Argon at room temperature?
5. Which period of the periodic table is Argon in?
Argon FAQs
What is the atomic number of argon?
Argon's atomic number is 18 — every argon atom has 18 protons in its nucleus.
What is the symbol for argon?
Ar. From Greek argos, meaning lazy or inactive.
Is argon a metal, nonmetal, or metalloid?
Argon is classified as a noble gas.
What state is argon at room temperature?
At about 25 °C, argon is a gas. It melts at -189.34 °C.
How many valence electrons does argon have?
Argon has 8 electrons in its outer shell (shell pattern: 2, 8, 8).
What is argon used for?
Key uses include: shield gas for welding; filling incandescent and fluorescent bulbs; insulating layer in double-glazed windows.
Related elements
Keep working with this element
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