Arsenic
Atomic Data
| Atomic Number | 33 |
| Symbol | As |
| Atomic Weight | 74.922 u |
| Density (STP) | 5.727 g/cm³ |
| Melting Point | 816.85 °C (1090 K) |
| Boiling Point | 613.85 °C (887 K) |
| Electronegativity | 2.18 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p3 |
| Oxidation States | −3, +3, +5 |
| Phase at STP | Solid |
| Category | Metalloid |
| Period / Group | 4 / 15 |
| CAS Number | 7440-38-2 |
Electron Configuration
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[Ar] 3d10 4s2 4p3
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 3 | 33 |
| Total | 33 | 33 | ||
Isotopes of Arsenic
Arsenic is monoisotopic — ⁷⁵As is its only naturally occurring stable isotope, accounting for 100% of all natural Arsenic.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Arsenic-75 | ⁷⁵As | 33 | 42 | 100 | Stable |
Abundance & Occurrence
Arsenic is present in Earth's crust at approximately 1.8 ppm by mass and at approximately 3 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Arsenic
1.8 ppm
Silicon (ref.)
277,000 ppm
Oxygen (ref.)
461,000 ppm
Universe (ppm by mass)
Arsenic
3 ppm
Helium (ref.)
230,000 ppm
Hydrogen (ref.)
739,000 ppm
Discovery & History
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Safety & Handling
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Arsenic in the Real World
Real-World Uses
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Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.