18
Room of the Elements · No. 18
Argon (Ar): what kind of element is it?
日本語
In short
Argon is element number 18, with the symbol Ar. 0.93% of dry air is argon, making it the most common gas in the air after nitrogen and oxygen.
Atomic number 1839.95
ArArgonアルゴン (arugon)- Symbol
- Ar
- Atomic weight
- 39.95
- Place in the table
- Period 3 · Group 18
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Third in the air
Dry air is almost all nitrogen (78.1%) and oxygen (20.9%). Next comes argon, at 0.93%.
Argon was discovered in 1894. Even though it makes up about 1 part in 100 of the air, it was found much later than nitrogen (1772) and oxygen (1774).
Named “idle”
The symbol Ar comes from the Greek argos, from “not” and “work,” because argon hardly reacts with anything.
Argon belongs to Group 18, the far-right column, and is a noble gas like helium and neon.
Think about it
- Q1Argon makes up about 1% of the air. Why do you think it was found so late?
- Q2What might a gas that hardly reacts with anything be useful for?
- Q3Can you name the three most common gases in the air, in order?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — When the noble gases were discovered one after another, a new column was added at the far right of the periodic table.