---
title: "Mendelevium (Md) — element 101"
description: "Mendelevium is element 101, symbol Md, most stable isotope 258. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/mendelevium/
site: "At One Place"
---

# Mendelevium (Md)

**Mendelevium — element 101: Md**

[258] · Actinide · period 7

Mendelevium was the first element made and identified one atom at a time. The Berkeley team bombarded about a billion einsteinium atoms with alpha particles and expected roughly one mendelevium atom per experiment; they ran it seventeen times and detected seventeen atoms, catching each on a gold foil and identifying it by the way it decayed. Naming it after Dmitri Mendeleev was politically awkward in 1955, honouring a Russian at the height of the Cold War, and the Berkeley group had to argue the point.

## Properties

- **Atomic number:** 101
- **Symbol:** Md
- **Mass number of most stable isotope:** [258]
- **Category:** Actinide
- **Period:** 7
- **Block:** f-block
- **Electron configuration:** [Rn] 7s² 5f¹³
- **Electrons per shell:** 2, 8, 18, 32, 31, 8, 2
- **Oxidation states:** +3, +2
- **Discovered:** 1955 by Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹³
- **Noble gas shorthand:** [Rn] 7s² 5f¹³
- **Shells:** K: 2 · L: 8 · M: 18 · N: 32 · O: 31 · P: 8 · Q: 2

## What it is used for

- Research only; no application outside the laboratory

## Hazards

- Intensely radioactive; only a few million atoms have ever been made

> Melting point, boiling point, density and electronegativity are omitted: no measured values exist, only extrapolations. The mass given is the mass number of mendelevium-258, the longest-lived at 51.5 days.

> Several physical properties are not listed for mendelevium because no bulk sample has ever existed. Only a handful of atoms have been produced, often with half-lives measured in seconds, so published melting points and densities for elements in this range are calculations rather than measurements. They are omitted rather than presented as observed values.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 99 | Einsteinium | Es | [252] |
| 100 | Fermium | Fm | [257] |
| 101 | Mendelevium ← | Md | [258] |
| 102 | Nobelium | No | [259] |
| 103 | Lawrencium | Lr | [266] |

## Common questions

### What is the atomic number of mendelevium?

101. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for mendelevium?

Md.

### What is the electron configuration of mendelevium?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹³, or [Rn] 7s² 5f¹³ in noble-gas shorthand.

## Related pages

- [Einsteinium (Es)](https://atoneplace.net/element/einsteinium/)
- [Fermium (Fm)](https://atoneplace.net/element/fermium/)
- [Nobelium (No)](https://atoneplace.net/element/nobelium/)
- [Lawrencium (Lr)](https://atoneplace.net/element/lawrencium/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)