Find arsenic's oxidation state in arsine gas, AsH3, and in As2O5.
AsH3: H is +1, so As = -3. As2O5: five O at -2 give -10, so 2As = +10, As = +5. Same element spans eight oxidation units depending on partner.
What Is the Charge of Arsenic?
Arsenic commonly forms As3- As3+ As5+ in introductory ionic compounds.
Arsenic mirrors phosphorus above it: -3 in metal arsenides (GaAs), +3 in arsenites and the infamous poison As2O3, and +5 in arsenates (AsO4 3-). Toxicologically the states differ sharply — arsenite (+3) is considerably more toxic than arsenate (+5).
| Element | Arsenic |
|---|---|
| Symbol | As |
| Atomic number | 33 |
| Common ionic charge | -3, +3, +5 |
| Common ions | As3-, As3+, As5+ |
Visual reference
Arsenic element image and atomic model
Images are used as visual references; charge rules still depend on the compound.
What Arsenic's electrons actually do
Arsenic is [Ar]3d10 4s2 4p3, three electrons short of a full shell — hence -3 with metals. Against oxygen, either just the three p electrons engage (+3) or all five valence electrons do (+5). Its metalloid character means all these compounds lean covalent.
Where intuition fails with Arsenic
Writing arsenate like a 1- ion. Arsenate is AsO4 3-, a direct analog of phosphate — three negative charges. Calcium arsenate, the old orchard insecticide, is Ca3(AsO4)2, matching calcium phosphate's pattern.
Worked example: As in a formula problem
As3- and As3+ and As5+ in real compounds
Na3As
sodium arsenic compound
Sodium ions can balance As3- in simple ionic examples.
CaAs2
calcium arsenic compound
Calcium ions can balance common negative Arsenic ions.
Questions students ask about arsenic
Why does arsenate poison cells if it's the 'less toxic' state?
AsO4 3- impersonates phosphate so well that enzymes install it into ATP-making pathways, where it promptly hydrolyzes and wastes the cell's energy. Chemical mimicry, courtesy of matching charge and shape.
What charge does arsenic have in contaminated groundwater?
Both +3 (arsenite, dominant in oxygen-poor wells) and +5 (arsenate, in aerated water). Treatment plants often oxidize everything to +5 first because arsenate sticks better to filter media.
Is gallium arsenide dangerous because of the arsenic?
Intact GaAs wafers lock arsenic (formally -3) into a stable lattice. The hazard arises in manufacturing dust and fumes, where arsenic escapes that lattice and oxidizes to its toxic states.
How do I use this charge in formulas?
Combine positive and negative ions so the total charge is zero — or let the ionic compound calculator do the crossing for you. The full chart lives on the periodic table with charges.
Where this data comes from
Charges and element facts on this page are checked against the primary references below. Found an error? Email hello@periodictablewithcharges.com — corrections ship in the next content update. See how this site is edited.