Protactinium is element number 91, with the symbol Pa. Its name combines the Greek for “first” with “actinium.”
Atomic number 91231.0
PaProtactiniumプロトアクチニウム (purotoakuchiniumu)
Symbol
Pa
Atomic weight
231.0
Place in the table
Period 7 · Actinoids
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Before actinium
Protactinium was discovered in 1918. Its name combines the Greek word for “first” with actinium, and it is linked to radioactive decay, the way elements give off radiation and change.
Where it sits on the table
The fifteen elements from actinium to lawrencium are called the actinoids. On the Room of the Elements table they are in the lower of the two rows set apart at the bottom.
Think about it
Q1How did you feel on learning that an element can change into another?
Q2Look for element names based on other elements (radon comes from radium).
Q3Do you know other words that use “proto”?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — Element names built from other elements’ names: protactinium (actinium) and radon (radium).