Plutonium is element number 94, with the symbol Pu. Its name comes from Pluto, the king of the underworld in Greek myth, and Pluto, named after him.
Atomic number 94(239)
PuPlutoniumプルトニウム (purutoniumu)
Symbol
Pu
Atomic weight
(239)
Place in the table
Period 7 · Actinoids
The number in parentheses is not an atomic weight. It is the mass number of one radioactive isotope of the element.
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
The underworld king and Pluto
Plutonium was discovered in 1940. Following uranium (Uranus) and neptunium (Neptune), it was named after Pluto.
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
Q1What do you think of naming elements in the order of the planets’ names?
Q2Compare the underworld king with the Titans, giants shut away underground (titanium).
Q3Look for actinoids named after myths.
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — Elements named after heavenly bodies: helium (Sun), selenium (Moon), tellurium (Earth), uranium, neptunium, plutonium, and the asteroid-named cerium and palladium.