Krypton is element number 36, with the symbol Kr. Its name comes from kryptos, the Greek word for “hidden.”
Atomic number 3683.80
KrKryptonクリプトン (kuriputon)
Symbol
Kr
Atomic weight
83.80
Place in the table
Period 4 · Group 18
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Hidden in the air
Krypton was discovered in 1898. Scientists cooled air until it became liquid and then separated its parts little by little, finding krypton as an element hidden in the air.
In the same year, neon (“new”) and xenon (“stranger”) were also discovered.
A noble gas in Group 18
Krypton belongs to Group 18, the far-right column, and is a noble gas like helium, neon and argon.
Krypton ends the fourth row. From hydrogen (1) to krypton (36), the top four rows of the periodic table are complete.
Think about it
Q1Why would turning air into a liquid and separating it reveal hidden elements?
Q2“New,” “hidden,” “stranger.” What feelings of the discoverers do the noble gas names suggest?
Q3How many elements are in the first four rows of the periodic table?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — 1898 was the year of neon, krypton and xenon, and also of polonium and radium.