Einsteinium is element number 99, with the symbol Es. Its name comes from the theoretical physicist Einstein.
Atomic number 99(252)
EsEinsteiniumアインスタイニウム (ainsutainiumu)
Symbol
Es
Atomic weight
(252)
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)”.
A physicist’s name
Einsteinium was discovered in 1953 and named after the theoretical physicist Einstein. Fermium, named after Fermi, was also discovered in 1953.
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 know about Einstein?
Q2Why do you think two elements found in the same year were named after two physicists?
Q3Collect the elements named after people in the Room of the Elements.
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — From 99 to 103, elements named after people follow one another: Einstein, Fermi, Mendeleev, Nobel and Lawrence.