Fermium (Fm)

Fermium properties

Atomic number

100

Atomic mass

257 u

Category

Actinide

Group

—

Period

7

Block

f-block

State at room temp.

Solid

Electronegativity

1.3

Melting point

1,800 K (1,526.8 °C)

Boiling point

—

Density

—

Valence electrons

2

Common charges

+3

Oxidation states

+3

Atomic radius

—

Ionization energy

6.5 eV

Electron affinity

—

Radioactive

Yes, no stable isotopes

Discovered

1952

Fermium electron configuration

The electron configuration of Fermium (Fm) is [Rn] 5f12 7s2. Its 100 electrons are arranged in shells as 2, 8, 18, 32, 30, 8, 2.

Protons, neutrons and electrons in Fermium

A neutral Fermium atom has 100 protons and 100 electrons. Most Fermium atoms have about 157 neutrons: the atomic mass rounded to 257, minus the atomic number 100.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Fermium have?

2

Fermium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.

See every element: Periodic table with valence electrons

Fermium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Fermium

257 g/mol

One mole of Fermium atoms (6.022 × 10²³ atoms) has a mass of 257 grams. Use this value to convert between grams and moles.

Fermium facts

• Fermium is the heaviest element that can be made by bombarding lighter elements with neutrons; heavier elements require particle accelerators.
• Fermium and einsteinium are the only elements first discovered in the debris of a nuclear explosion.
• Fermium (Fm) has atomic number 100 and is a solid at room temperature. It was discovered in 1952.

Position in the periodic table

Fermium is element 100, in period 7 of the periodic table. It is one of the Actinides in the f-block, shown in the rows below the main table.

All actinides

Uses of Fermium

Fermium has no practical uses because only tiny amounts have ever been produced, and even its longest-lived isotope lasts only about 100 days. Scientists study it to understand the chemistry of the heaviest actinides and how very heavy nuclei split apart in nuclear fission.

Who discovered Fermium?

Albert Ghiorso's team at Berkeley, working with Argonne and Los Alamos scientists, found fermium in 1952 in the debris of the 'Ivy Mike' hydrogen bomb test. It was named after Italian-American physicist Enrico Fermi.

Where does the name come from?

Fermium honors Enrico Fermi, the Italian-born physicist who built the first nuclear reactor. Like einsteinium, it was discovered in the debris of the 1952 hydrogen bomb test, though the finding was kept secret for several years.

Discovery timeline