---
title: "Arsenic (As): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/arsenic.html
description: "Arsenic (As), element 33: atomic mass 74.922, electron configuration [Ar] 3d¹⁰ 4s² 4p³, group 15, period 4, p-block metalloid. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
33As74.922

# Arsenic (As) – element 33

Arsenic is a chemical element with the symbol **As** and atomic number **33**. It is a metalloid in group 15 (pnictogens), period 4 of the periodic table (p-block), and is a solid at room temperature.

Arsenic (As) has atomic number 33, atomic mass 74.922 u and electron configuration [Ar] 3d10 4s2 4p3.

[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)

## Arsenic facts

| Symbol | As |
| --- | --- |
| Atomic number | 33 |
| Atomic mass | 74.922 u (g/mol) |
| Category | metalloid |
| Group | group 15 (pnictogens) |
| Period | 4 |
| Block | p-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3 |
| Noble-gas notation | [Ar] 3d10 4s2 4p3 |
| Electrons per shell | 2, 8, 18, 5 |
| Valence electrons | 5 |

## Bohr model and shells

Arsenic has 33 electrons in 4 shells: 2, 8, 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 | 1090 K (816.9 °C) |
| --- | --- |
| Density | 5.727 g/cm³ |
| Electronegativity (Pauling) | 2.18 |
| Electron affinity | 77.65 kJ/mol |
| Ionization energies | 947, 1798, 2735 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 24.64 J/(mol·K) |
| Discovered by | Bronze Age |

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 As.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of arsenic?

The atomic mass of arsenic is 74.922 u, so one mole of arsenic atoms weighs 74.922 g.

### What is the electron configuration of arsenic?

Arsenic has 33 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³, or [Ar] 3d¹⁰ 4s² 4p³ in noble-gas notation. Electrons per shell: 2, 8, 18, 5.

### How many valence electrons does arsenic have?

Arsenic has 5 valence electrons (group 15).

### Is arsenic a metal?

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

### Where is arsenic on the periodic table?

Arsenic is in group 15 (pnictogens), period 4, 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.