---
title: "Antimony (Sb): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/antimony.html
description: "Antimony (Sb), element 51: atomic mass 121.76, electron configuration [Kr] 4d¹⁰ 5s² 5p³, group 15, period 5, p-block metalloid. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
51Sb121.76

# Antimony (Sb) – element 51

Antimony is a chemical element with the symbol **Sb** and atomic number **51**. It is a metalloid in group 15 (pnictogens), period 5 of the periodic table (p-block), and is a solid at room temperature.

Antimony (Sb) has atomic number 51, atomic mass 121.76 u and electron configuration [Kr] 4d10 5s2 5p3.

[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)

## Antimony facts

| Symbol | Sb |
| --- | --- |
| Atomic number | 51 |
| Atomic mass | 121.76 u (g/mol) |
| Category | metalloid |
| Group | group 15 (pnictogens) |
| Period | 5 |
| Block | p-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p3 |
| Noble-gas notation | [Kr] 4d10 5s2 5p3 |
| Electrons per shell | 2, 8, 18, 18, 5 |
| Valence electrons | 5 |

## Bohr model and shells

Antimony has 51 electrons in 5 shells: 2, 8, 18, 18, 5. 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 | 903.78 K (630.6 °C) |
| --- | --- |
| Boiling point | 1908 K (1634.8 °C) |
| Density | 6.697 g/cm³ |
| Electronegativity (Pauling) | 2.05 |
| Electron affinity | 101.059 kJ/mol |
| Ionization energies | 834, 1594.9, 2440 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 25.23 J/(mol·K) |
| Discovered by | unknown, before 3000 BC |

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 Sb.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of antimony?

The atomic mass of antimony is 121.76 u, so one mole of antimony atoms weighs 121.76 g.

### What is the electron configuration of antimony?

Antimony has 51 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p³, or [Kr] 4d¹⁰ 5s² 5p³ in noble-gas notation. Electrons per shell: 2, 8, 18, 18, 5.

### How many valence electrons does antimony have?

Antimony has 5 valence electrons (group 15).

### Is antimony a metal?

Antimony is a metalloid: it has properties between metals and nonmetals.

### Where is antimony on the periodic table?

Antimony is in group 15 (pnictogens), period 5, in the p-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.