---
title: "Boron (B): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/boron.html
description: "Boron (B), element 5: atomic mass 10.81, electron configuration [He] 2s² 2p¹, group 13, period 2, p-block metalloid. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
5B10.81

# Boron (B) – element 5

Boron is a chemical element with the symbol **B** and atomic number **5**. It is a metalloid in group 13, period 2 of the periodic table (p-block), and is a solid at room temperature.

Boron (B) has atomic number 5, atomic mass 10.81 u and electron configuration [He] 2s2 2p1.

[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)

## Boron facts

| Symbol | B |
| --- | --- |
| Atomic number | 5 |
| Atomic mass | 10.81 u (g/mol) |
| Category | metalloid |
| Group | group 13 |
| Period | 2 |
| Block | p-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p1 |
| Noble-gas notation | [He] 2s2 2p1 |
| Electrons per shell | 2, 3 |
| Valence electrons | 3 |

## Bohr model and shells

Boron has 5 electrons in 2 shells: 2, 3. 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 | 2349 K (2075.8 °C) |
| --- | --- |
| Boiling point | 4200 K (3926.8 °C) |
| Density | 2.08 g/cm³ |
| Electronegativity (Pauling) | 2.04 |
| Electron affinity | 26.989 kJ/mol |
| Ionization energies | 800.6, 2427.1, 3659.7 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 11.087 J/(mol·K) |
| Discovered by | Joseph Louis Gay-Lussac |

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 B.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of boron?

The atomic mass of boron is 10.81 u, so one mole of boron atoms weighs 10.81 g.

### What is the electron configuration of boron?

Boron has 5 electrons: 1s² 2s² 2p¹, or [He] 2s² 2p¹ in noble-gas notation. Electrons per shell: 2, 3.

### How many valence electrons does boron have?

Boron has 3 valence electrons (group 13).

### Is boron a metal?

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

### Where is boron on the periodic table?

Boron is in group 13, period 2, 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.