Potassium is element number 19, with the symbol K. In the body, it is the main positive ion in the fluid inside our cells. It is also one of the three main nutrients in fertilizer.
Atomic number 1939.10
KPotassiumカリウム (kariumu)
Symbol
K
Atomic weight
39.10
Place in the table
Period 4 · Group 1
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Why the symbol is K
The symbol is K because it comes from the Latin name kalium, not from the English word.
Kalium comes from the Arabic qali, meaning the juice of plants. The English “potassium” comes from “pot ashes.” Both names come from things obtained from plants.
Potassium in the body and in the fields
Potassium is the main positive ion inside our cells and an important factor in setting how concentrated our body fluids are. It also plays a part when nerves and muscles work.
The three main fertilizer nutrients are nitrogen, phosphate and potassium. In Japanese farming, potassium is also written カリ (kari) or 加里.
Think about it
Q1Spreading plant ash on fields is an old farming practice. Why might it help?
Q2Find elements on the periodic table whose symbol does not match the first letter of their English name.
Q3Sodium is outside the cells and potassium is inside. Why might they be separated?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — Potassium and sodium (Na) are both in Group 1, and both were discovered in 1807.