Atomic data
Reference atomic data and stable ⁷⁵As identity are evaluated.
Gray arsenic structure
Rhombohedral A7-type gray arsenic structure is measured.
Sublimation path
Ordinary-pressure teaching path uses sublimation near 889 K and does not fabricate a liquid interval.
Species / safety
Elemental arsenic and chemical species are kept distinct.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Arsenic (As)
Arsenic is element 33, a Group 15 metalloid with multiple allotropes and oxidation states. Gray arsenic is a layered solid, while yellow arsenic contains As₄ molecules; arsenic compounds also require careful species-specific toxicity language.
Arsenic atomic number, mass, electron configuration and key properties
Arsenic: quick answers
How many protons, neutrons and electrons does arsenic have?
Arsenic’s atomic number is 33, so every arsenic atom has 33 protons, and a neutral atom also has 33 electrons. Its most common natural isotope, arsenic-75, has 42 neutrons (other isotopes have different neutron counts).
What is the symbol for arsenic?
The chemical symbol for arsenic is As.
Is arsenic a solid, liquid or gas at room temperature?
Arsenic is a solid at room temperature (about 25 °C).
What family (group) is arsenic in?
Arsenic is a metalloid, in group 15, period 4 of the periodic table.
How many valence electrons does arsenic have?
Arsenic has 5 valence electrons, the electrons in its outer shell, which matches its position in group 15.
What is the electron configuration of arsenic?
The ground-state electron configuration of arsenic is [Ar] 3d¹⁰ 4s² 4p³.
From atomic number to chemistry
Read these as a chain of causes, not as isolated facts. Each step links to the concept hub if you want the underlying idea explained.
33 protons define arsenic.
The reference ground-state configuration frames atomic and chemical behavior.
Periodic position organizes recurring trends without replacing element-specific evidence.
The teaching nucleus is one isotope, not the relative atomic mass.
Phase claims preserve measured/evaluated/predicted/unknown evidence labels.
Arsenic in its period and family
Arsenic is the Period 4 Group 15 metalloid between germanium and selenium. Its 4s²4p³ valence shell supports −3, +3 and +5 chemistry, but elemental allotropes and compounds have distinct structures.
Arsenic Visual Lab
Rotate a ⁷⁵As nucleus and gray-arsenic rhombohedral teaching cell, inspect 4s/4p probability clouds, then compare gray-network arsenic with molecular As₄ and the ordinary-pressure sublimation path.
Every mark points to one exact feature
The numbered markers explain the same information system used throughout Element Lookup. Unknown or predicted fields remain visibly labelled rather than being replaced with guesses.
Arsenic in one minute
Atomic number 33 means 33 protons.
Natural arsenic is essentially ⁷⁵As.
Gray arsenic is the stable ordinary allotrope and has a rhombohedral layered structure.
At ordinary pressure arsenic sublimes rather than following a simple solid→liquid→gas path.
Chemical species matters critically when discussing arsenic toxicity and uses.
Shell rings organize electron counts. They are not electron trajectories or orbital shapes.
2 · 8 · 18 · 5 electrons
The 4s/4p clouds describe an isolated arsenic atom. They are not a model of gray-arsenic bands, As₄ molecular orbitals or arsenic compounds.
Stable gray arsenic has a layered rhombohedral A7-type structure. The viewer is a simplified rhombohedral teaching cell; yellow arsenic is molecular As₄ and is a different allotrope.. The viewer is evidence-aware: measured structures are identified as such; unknown bulk structures stay unknown.
Teaching visualization; not a literal finite sample or thermal trajectory.What this model does—and does not—show
The 4s/4p clouds describe an isolated arsenic atom. They are not a model of gray-arsenic bands, As₄ molecular orbitals or arsenic compounds.
Where do I meet arsenic?
Clickable learning cards connect the element to materials, environment, technology, biology or research - depending on what the evidence actually supports.
Allotropes
Gray arsenic is a layered rhombohedral solid; yellow arsenic is molecular As₄ and less stable under ordinary conditions.
Gray network arsenic ↔ yellow As₄ ↔ compound/species chemistry
Arsenic shows why allotrope and chemical species must be specified before discussing structure, use or hazard.
Rhombohedral network
Stable gray arsenic is a layered A7-type metalloid solid.
Phosphorus, arsenic and antimony
Five outer electrons support diverse allotropes and a progression toward more metallic character.
| Valence | 3s²3p³ |
|---|---|
| Allotropes | white/red/black |
| Valence | 4s²4p³ |
|---|---|
| Stable form | gray A7 |
| Valence | 5s²5p³ |
|---|---|
| Context | metalloid |
Arsenic properties: atomic, physical, thermal and chemical
Categories follow the science of this element rather than a fixed decorative template. Each row carries condition/provenance context and an evidence label; unknown values stay unknown.
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Atomic number | 33 | Source-reviewed; see Sources below | Evaluated |
| Relative atomic mass | 74.922 | Source-reviewed; see Sources below | Evaluated |
| Ground-state electron configuration | [Ar] 3d¹⁰ 4s² 4p³ | Source-reviewed; see Sources below | Evaluated |
| Group / period / block | Group 15 · Period 4 · p-block | Periodic-table placement | Evaluated |
| Electronegativity | 2.18 | Source-reviewed; see Sources below | Evaluated |
| Reference isotope | ⁷⁵As | Source-reviewed; see Sources below | Evaluated |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| State context | Gray arsenic is a brittle metalloid solid at 20 °C | Source-reviewed; see Sources below | Evaluated |
| Density | 5.75 g/cm³ (gray arsenic) | Source-reviewed; see Sources below | Evaluated |
| Material / molecular structure | Gray arsenic · rhombohedral A7-type network | Stable gray arsenic has a layered rhombohedral A7-type structure. The viewer is a simplified rhombohedral teaching cell; yellow arsenic is molecular As₄ and is a different allotrope. | Measured |
| Classification | Metalloid | Periodic-table / chemistry classification | Evaluated |
| Structure-model scope | Stable gray arsenic has a layered rhombohedral A7-type structure. The viewer is a simplified rhombohedral teaching cell; yellow arsenic is molecular As₄ and is a different allotrope. | Teaching visualization; exact crystallographic coordinates are not implied unless stated. | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Melting / transition reference | Sublimes near 889 K at ordinary pressure | Source-reviewed; see Sources below | Evaluated |
| Boiling / gas reference | No ordinary-pressure liquid/boiling path; arsenic sublimes | Source-reviewed; see Sources below | Evaluated |
| Phase-path context | At ordinary pressure gray arsenic is solid over the displayed low-temperature range and sublimes to vapor near 889 K. A normal liquid interval is not fabricated for this path. | Shared phase registry drives the slider, regions and markers. | Evaluated |
| Condition warning | Temperature and pressure define phase behavior; purity/allotropy may matter. | Teaching condition statement | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Common oxidation states | −3, +3, +5 | Source-reviewed; see Sources below | Evaluated |
| Ion / common ion context | Element-specific; see chemistry sections | Source-reviewed; see Sources below | Evaluated |
| Periodic chemistry context | Arsenic is the Period 4 Group 15 metalloid between germanium and selenium. Its 4s²4p³ valence shell supports −3, +3 and +5 chemistry, but elemental allotropes and compounds have distinct structures. | Element-specific interpretation | Reviewed |
| Chemistry caution | Elemental form, ions and compounds are distinct chemical objects. | Interpretive teaching rule | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| ⁷⁵As | Stable natural isotope | Reference teaching nucleus with 33 protons and 42 neutrons. | Evaluated |
| Arsenic isotope context | One stable natural isotope | Natural arsenic is essentially monoisotopic. | Evaluated |
| Radioarsenic isotopes | Research/medical tracer context | Specialized radioactive isotopes exist but are distinct from natural bulk arsenic. | Evaluated |
| Teaching nucleus | ⁷⁵As · 33 protons + 42 neutrons | Reference isotope used in the nucleus model | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Page evidence note | Atomic and gray-arsenic bulk values are evaluated. The ordinary-pressure phase path explicitly uses sublimation rather than inventing a liquid range. Commodity points are selected current contexts, not a global exposure map. | Evidence summary for this guide | Reviewed |
| Structure evidence | Stable gray arsenic has a layered rhombohedral A7-type structure. The viewer is a simplified rhombohedral teaching cell; yellow arsenic is molecular As₄ and is a different allotrope. | Measured structure, labelled schematic, prediction or explicit unknown as applicable. | Reviewed |
| Map evidence rule | Real pins are reviewed examples; conceptual layers are used when pins would mislead. | Geography Explorer 2.0 | Reviewed |
| Source set | 3 primary/reference links listed below | Open the Sources section for the actual references. | Reviewed |
Is Arsenic a solid, liquid or gas? State at temperature
At ordinary pressure gray arsenic is solid over the displayed low-temperature range and sublimes to vapor near 889 K. A normal liquid interval is not fabricated for this path.
Where on Earth is Arsenic found or produced?
Who discovered Arsenic, and when?
Arsenic-containing minerals and compounds were known long before the element was isolated.
Methods for obtaining elemental arsenic from minerals became known in Europe.
Arsenic compounds saw broad industrial and agricultural use alongside growing recognition of toxicity.
Arsenic is managed as both a useful chemical constituent and a major environmental/public-health contaminant depending on species and exposure.
Arsenic in mineral processing: high-level context
Arsenic occurs in minerals such as arsenopyrite and in polymetallic ore systems.
During mining and smelting, arsenic-bearing phases may enter concentrates, off-gases, residues or controlled products.
Modern operations manage arsenic chemistry under strict environmental and occupational controls; this page does not provide extraction or treatment procedures.
Specialty semiconductor supply uses highly controlled purified arsenic feedstocks.
What is arsenic used for?
Semiconductors
Arsenic is used in compounds such as GaAs for electronics and optoelectronics.
Alloying / metallurgy
Small arsenic additions have specialized historical and metallurgical roles.
Research
Arsenic chemistry and speciation are important in environmental, geochemical and materials research.
Historical compounds
Some past pigment, pesticide and medicinal uses are now obsolete or restricted because of toxicity.
Arsenic isotopes and natural abundance
⁷⁵As
Stable natural isotopeReference teaching nucleus with 33 protons and 42 neutrons.
Arsenic isotope context
One stable natural isotopeNatural arsenic is essentially monoisotopic.
Radioarsenic isotopes
Research/medical tracer contextSpecialized radioactive isotopes exist but are distinct from natural bulk arsenic.
Five-question Arsenic check
What is arsenic’s atomic number?
How is arsenic commonly classified?
What happens near 889 K at ordinary pressure?
What is the only stable natural arsenic isotope?
Why should GaAs not be described as elemental arsenic?
Arsenic questions students commonly ask
Each answer starts with the direct fact, then explains the chemistry, evidence or material context so the result is understandable rather than merely memorized.
What is arsenic?
Short answer: Arsenic is element 33, a Group 15 metalloid with several allotropes and many compounds.
Atomic number 33 means every arsenic nucleus contains 33 protons. In the periodic table, Arsenic is classified here as a metalloid in Period 4 and Group 15. Arsenic is the Period 4 Group 15 metalloid between germanium and selenium. Its 4s²4p³ valence shell supports −3, +3 and +5 chemistry, but elemental allotropes and compounds have distinct structures.
Key point: As is element 33; its periodic position and electron structure explain the rest of the page.
Is arsenic a metal?
Short answer: It is usually classified as a metalloid rather than an ordinary metal.
This guide classifies Arsenic as a metalloid. Its periodic position is Period 4, p-block, Group 15. Arsenic is the Period 4 Group 15 metalloid between germanium and selenium. Its 4s²4p³ valence shell supports −3, +3 and +5 chemistry, but elemental allotropes and compounds have distinct structures.
Key point: Periodic-table classification describes recurring atomic/chemical behavior; it does not make every element in a column physically identical.
What is arsenic used for?
Short answer: Modern uses include specialized semiconductor compounds; many historical pesticide/pigment uses are restricted or obsolete.
Semiconductors: Arsenic is used in compounds such as GaAs for electronics and optoelectronics. Alloying / metallurgy: Small arsenic additions have specialized historical and metallurgical roles. “Arsenic” is not one exposure species. Elemental arsenic, arsenite/arsenate compounds, organoarsenic species and semiconductor compounds can have very different chemistry and hazards.
Key point: Always distinguish the pure element from the compound, alloy, isotope or device material that actually performs the application.
Does arsenic melt at ordinary pressure?
Short answer: The common teaching path is sublimation near 889 K rather than a normal liquid interval at ordinary pressure.
At ordinary pressure gray arsenic is solid over the displayed low-temperature range and sublimes to vapor near 889 K. A normal liquid interval is not fabricated for this path. At ordinary pressure arsenic sublimes rather than following a simple solid→liquid→gas path.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
How many valence electrons does arsenic have?
Short answer: Five in the simple outer-shell count, 4s²4p³.
The neutral-atom ground-state reference used on this page is [Ar] 3d¹⁰ 4s² 4p³. This is an isolated-atom reference: bonding and ion formation can change which outer electrons are present or chemically active. The listed common oxidation-state context is −3, +3, +5, which helps connect the atomic configuration to ordinary chemistry without treating electron counting as a single universal rule.
Key point: Electron configuration is a ground-state atomic reference, not a literal picture of every compound.
Why does arsenic safety depend on species?
Short answer: Different arsenic compounds and oxidation states differ in mobility, bioavailability and toxicity.
Arsenic and many inorganic arsenic compounds are toxic. This page provides chemistry education only, not exposure, treatment, remediation or handling instructions.
Key point: Safety claims must be substance- and exposure-specific.
Scientific sources for Arsenic
- Royal Society of Chemistry - Arsenic
- NIST - Atomic Data for Arsenic
- USGS - Mineral Commodity Summaries 2026
Questions to ask next about Arsenic
A good element lesson should lead to the next useful question, not end after a list of facts.
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