Hydrogen is element number 1, with the symbol H. It is the lightest of all the elements and the most common element in the universe. When it joins with oxygen, it becomes water.
Atomic number 11.008
HHydrogen水素 (suiso)
Symbol
H
Atomic weight
1.008
Place in the table
Period 1 · Group 1
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
The lightest, and the most common
Chemists compare how heavy elements are by their “atomic weight.” Hydrogen’s is 1.008, the smallest of all 118 elements. It sits in the top-left corner of the periodic table, in square number 1.
About three minutes after the universe was born, the first nuclei of hydrogen and helium formed. The National Astronomical Observatory of Japan explains that before stars formed, hydrogen made up three-quarters of the mass of all atomic nuclei in the universe. Even today, hydrogen and helium are by far the most common elements in the universe.
“Water-source”: hydrogen’s name in Japanese and in English
In Japanese, hydrogen is called 水素 (suiso). The name was created by Udagawa Yōan, a scholar of the Edo period who learned Western chemistry from Dutch books. From 1837 (Tenpō 8) he published Seimi Kaisō, the first book in Japan to present chemistry as a whole field of study.
In Dutch, hydrogen is waterstof: water is water, and stof means the stuff something is made from. Yōan translated it piece by piece into 水 (water) + 素 (source) = 水素, “water-source.” The Japanese words for oxygen, carbon and nitrogen, and the word for “element” itself (元素), were also coined by Yōan.
The symbol H comes from the scientific Latin name hydrogenium, built from the Greek hydor (water) and genes (producing): “water-maker.” The English and the Japanese names both point to water.
Yōan wrote that water is not a single pure substance but is made of hydrogen and oxygen. In Japanese junior high school science, splitting water with an electric current is one of the example experiments in the national curriculum guide.
Think about it
Q1Water is made of hydrogen and oxygen. How did you feel when you first heard that?
Q2The Japanese names 酸素 (oxygen), 窒素 (nitrogen) and 炭素 (carbon) all end in 素, “source.” What do you think each one is the source of?
Q3Hydrogen is the most common element in the universe. Where do we see or use hydrogen in our lives?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — Hydrogen can also be rocket fuel. On 13 October 1973, a team at Japan’s Institute of Space and Astronautical Science succeeded, for the first time in Japan, in a firing test of an engine that burns liquid hydrogen with liquid oxygen.