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Arsenic

Element 33 · Metalloid

Specimen

Atomic number
33
Atomic mass
74.922
State at room temperature
Solid
Melting point
816.9 °C
Boiling point
613.9 °C
Density
5.776 g/cm³
Discovered
Ancient

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Poison. Inorganic arsenic, mostly from polluted groundwater, is highly toxic. Long-term intake causes skin lesions and cancer. Organic arsenic in seafood is less harmful. 3

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The atom

As
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) outermost 5
Total33

Configuration [Ar] 3d¹⁰ 4s² 4p³

3d ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓
4s ↑ ↓
4p ↑ ↑ ↑
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 33 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Ar core, with one arrow per electron.

Related elements

Group 15
N Nitrogen P Phosphorus Sb Antimony Bi Bismuth Mc Moscovium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    World Health Organization, 2022. Arsenic (fact sheet) .

    • Long-term exposure to inorganic arsenic, mainly through drinking-water and food, can lead to chronic arsenic poisoning. Skin lesions and skin cancer are the most characteristic effects.
    • Inorganic arsenic compounds (such as those found in water) are highly toxic while organic arsenic compounds (such as those found in seafood) are less harmful to health.
  4. 4

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.