---
title: "Fermium (Fm): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/fermium.html
description: "Fermium (Fm), element 100: atomic mass [257], electron configuration [Rn] 5f¹² 7s², group 3, period 7, f-block actinide. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
100Fm[257]

# Fermium (Fm) – element 100

Fermium is a chemical element with the symbol **Fm** and atomic number **100**. It is a actinide in group 3 (actinides), period 7 of the periodic table (f-block), and is a solid at room temperature.

Fermium (Fm) has atomic number 100, atomic mass [257] and electron configuration [Rn] 5f12 7s2.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Fermium facts

| Symbol | Fm |
| --- | --- |
| Atomic number | 100 |
| Atomic mass | [257] |
| Category | actinide |
| Group | group 3 (actinides) |
| Period | 7 |
| Block | f-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f12 |
| Noble-gas notation | [Rn] 5f12 7s2 |
| Electrons per shell | 2, 8, 18, 32, 30, 8, 2 |

## Bohr model and shells

Fermium has 100 electrons in 7 shells: 2, 8, 18, 32, 30, 8, 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 1800 K (1526.8 °C) |
| --- | --- |
| Electronegativity (Pauling) | 1.3 |
| Electron affinity | 33.96 kJ/mol |
| Ionization energies | 627 kJ/mol (1st) |
| Discovered by | Lawrence Berkeley National Laboratory |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing Fm.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of fermium?

The atomic mass of fermium is [257] (mass number of its longest-lived isotope, since it has no stable isotope).

### What is the electron configuration of fermium?

Fermium has 100 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹², or [Rn] 5f¹² 7s² in noble-gas notation. Electrons per shell: 2, 8, 18, 32, 30, 8, 2.

### Is fermium a metal?

Yes. Fermium is a actinide.

### Where is fermium on the periodic table?

Fermium is in group 3 (actinides), period 7, in the f-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.