What is Arsenic's atomic number?

Arsenic has atomic number 33, meaning it has 33 protons in its nucleus. Its chemical symbol is As, derived from the Latin arsenicum.

Is Arsenic a metal or nonmetal?

Arsenic is classified as a metalloid (or semimetal). It exhibits properties intermediate between metals and nonmetals, with a metallic gray appearance but brittle, non-ductile behavior.

What is Arsenic used for today?

Modern uses include gallium arsenide (GaAs) semiconductors for high-speed electronics and solar cells, wood preservatives (formerly CCA), pesticides, and pharmaceutical compounds. It was historically used in pigments and medicines.

Why is Arsenic toxic?

Arsenic interferes with ATP production by binding to thiol groups in enzymes. Inorganic arsenic compounds (arsenite As3+ and arsenate As5+) are classified as Group 1 human carcinogens by the IARC.

What is Arsenic's electron configuration?

Arsenic's full electron configuration is [Ar] 3d10 4s2 4p3. The three 4p electrons give it common oxidation states of +3 and +5, plus -3 in arsenides.

Who discovered Arsenic?

Arsenic compounds have been known since antiquity. The element in its pure form is attributed to Albertus Magnus around 1250 AD, though the isolation method was refined over subsequent centuries.

Arsenic Element Properties

Explore the complete physical and chemical properties of Arsenic (As, element 33) — from its metalloid nature to its role in semiconductors and historical uses.

74.922

Arsenic

Metalloid · Period 4 · Group 15

Melting Point

817 °C

Sublimation Point

614 °C

Density

5.73 g/cm³

Atomic Mass

74.922 u

Electron Shell Configuration

[Ar] 3d¹⁰ 4s² 4p³

Shells: 2, 8, 18, 5

Filter Properties

Property	Value
Element Name	Arsenic
Symbol	As
Atomic Number	33
Atomic Mass	74.921595 u
Category	Metalloid
Group	15 (VA / Pnictogens)
Period	4
Block	p-block
CAS Number	7440-38-2
Discovered	c. 1250 AD (pure element)
Discovered By	Albertus Magnus (attributed)
Named After	arsenikon (Greek: yellow orpiment)
Standard State	Solid at 25 °C
Appearance	Metallic gray, brittle solid
Allotropes	Gray (stable), yellow, black, brown

Property	Value
Electron Configuration	[Ar] 3d10 4s2 4p3
Electrons Per Shell	2, 8, 18, 5
Number of Protons	33
Number of Neutrons (As-75)	42
Number of Electrons	33
Valence Electrons	5
Oxidation States	-3, 0, +3, +5
Electronegativity (Pauling)	2.18
Electron Affinity	78 kJ/mol
First Ionization Energy	947.0 kJ/mol
Second Ionization Energy	1798 kJ/mol
Third Ionization Energy	2736 kJ/mol
Atomic Radius (calc.)	114 pm
Covalent Radius	119 pm
Van der Waals Radius	185 pm
Stable Isotopes	As-75 (100% — monoisotopic)

Property	Value
Melting Point (at 28 atm)	817 °C (1503 °F / 1090 K)
Sublimation Point (1 atm)	614 °C (1137 °F / 887 K)
Boiling Point (1 atm)	Sublimes at 614 °C (887 K)
Density (gray arsenic)	5.73 g/cm³
Density (yellow arsenic)	1.97 g/cm³
Heat of Fusion	24.44 kJ/mol
Heat of Sublimation	32.4 kJ/mol
Heat of Vaporization	34.76 kJ/mol
Specific Heat Capacity	0.329 J/(g·K)
Thermal Conductivity	50.2 W/(m·K)
Electrical Resistivity	333 nΩ·m (at 20 °C)
Mohs Hardness	3.5
Brinell Hardness	1440 MPa
Crystal Structure	Rhombohedral (gray allotrope)
Magnetic Ordering	Diamagnetic
Speed of Sound	Not well-defined (brittle)

Property	Value
Reactivity	Moderate; oxidizes slowly in air
Reaction with Air	Forms As2O3 (white arsenic oxide) on heating
Reaction with Water	Very slow at room temperature
Reaction with Acids	Dissolves in HNO3 and hot H2SO4
Reaction with Halogens	Reacts readily; forms AsX3 halides
Common Compounds	As2O3, As2O5, AsH3 (arsine), GaAs, InAs
Key Semiconductor Use	Gallium arsenide (GaAs) — high-speed electronics
Key Toxic Form	Arsenite (As3+) and arsenate (As5+) in water
Oxidation State Range	-3, 0, +3, +5 (+3 and +5 most common)
Metalloid Behavior	Conducts electricity poorly; amphoteric oxides
Allotropism	Four allotropes: gray (stable), yellow, black, brown
Toxicity	High; IARC Group 1 carcinogen (inorganic forms)
Natural Occurrence	Found in arsenopyrite (FeAsS), realgar, orpiment
Global Production	~33,000 tonnes/year (primarily As2O3 from smelting)

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Summary

Arsenic (As) is element 33 on the periodic table, a metalloid in group 15 (pnictogens). It exists in several allotropic forms, the most stable being gray arsenic — a brittle, steel-gray solid. This reference tool presents all key physical, atomic, and chemical properties of Arsenic in one organized view, including its semiconductor uses, toxicity data, and historical significance.

How it works

All Arsenic property data is embedded directly in the page — no server call is needed.
Use the section tabs (Overview, Atomic, Physical, Chemical) to navigate different property groups.
Click any property row to copy its value to your clipboard.
The electron configuration diagram shows the shell distribution visually.
Use the search box to filter properties by name.

Use cases

Quick reference for students studying periodic table metalloids.
Verify Arsenic specs during semiconductor or materials research.
Teaching aid for illustrating metalloid properties and allotropism.
Cross-check Arsenic toxicology and environmental data for lab work.
Explore Arsenic's role in gallium arsenide (GaAs) semiconductors.
Support chemistry homework and exam preparation.
Reference oxidation states for analytical chemistry problems.
Look up thermodynamic data for thermochemistry calculations.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu