20
Room of the Elements · No. 20
Calcium (Ca): what kind of element is it?
日本語
In short
Calcium is element number 20, with the symbol Ca. It makes up 1–2% of our body weight, and 99% of it is in our bones and teeth.
Atomic number 2040.08
CaCalciumカルシウム (karushiumu)- Symbol
- Ca
- Atomic weight
- 40.08
- Place in the table
- Period 4 · Group 2
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Calcium in bones and teeth
Calcium makes up 1–2% of body weight. Of that, 99% is in bones and teeth, and the remaining 1% or so is in the blood and other body fluids and cells.
It is also one of the nine elements that plants need in large amounts.
Named for lime
The symbol Ca comes from calx, Latin for lime. Calcium was discovered in 1808.
Calcium is in Group 2 of the periodic table, the same column as magnesium, which is also found in large amounts in our bones.
Think about it
- Q1For a person who weighs 30 kg, about how many grams of calcium is 1–2% of their weight?
- Q2Is the calcium in our bones always the same calcium, or does it change?
- Q3Where is lime used around you?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — In 1808, three elements from the same column, Group 2, were discovered: calcium, magnesium and barium.
About this page
Symbol and atomic weight:
Chemical Society of Japan, “Table of Standard Atomic Weights (2026)” and “Table of Atomic Weights with Four Significant Figures (2026)”. Calcium in the body:
Ministry of Health, Labour and Welfare, “Dietary Reference Intakes for Japanese (2025)”, macrominerals. Origin of the symbol (
calx, 1808) and the discovery years of magnesium and barium:
Sugiyama, “The Origins of Element Symbols,” Kagaku to Kyōiku 43(12), 1995 (Chemical Society of Japan). Elements plants need in large amounts:
Ministry of Agriculture, Forestry and Fisheries, glossary on the fertilizer system. All sources are in Japanese.
Written by CCN CO., LTD.