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101
Room of the Elements · No. 101

Mendelevium (Md): what kind of element is it?

日本語

In short

Mendelevium is element number 101, with the symbol Md. It was named in honor of Mendeleev, who created the periodic table.
Atomic number 101(258)
MdMendelevium (menderebiumu)
Symbol
Md
Atomic weight
(258)
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 creator of the periodic table

Element 101, an artificial element discovered in 1955, was named mendelevium in honor of Mendeleev. His name would remain in the periodic table forever.

Mendeleev published his periodic table in 1869 and left gaps for undiscovered elements. Gallium, scandium and germanium were found just as he predicted.

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

There is no single right answer. Talking it over with someone at home is a good way to learn.

Did you know? — To make elements after number 101, machines called linear accelerators came into use.
Next steps
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)”. Origin of the symbol and year of discovery: Sugiyama, “The Origins of Element Symbols,” Kagaku to Kyōiku 43(12), 1995 (Chemical Society of Japan). The naming of mendelevium, Mendeleev’s predictions, and elements after 101 and linear accelerators: “International Year of the Periodic Table 2019 (150 years of the periodic table),” Kagaku to Kyōiku 67(6), 2019. All sources are in Japanese.
Written by CCN CO., LTD.
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