33AsArsenic74.921595 u
Arsenic (As)
Arsenic is a metalloid with atomic number 33, in period 4 and group 15 of the periodic table. Its atomic mass is 74.921595 u and its electron configuration is [Ar] 3d¹⁰ 4s² 4p³. Solid at 25 °C.
Key facts
| Atomic number | 33 |
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| Atomic mass | 74.921595 u |
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| Category | Metalloid |
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| Period | 4 |
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| Group | 15 |
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| Block | p |
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| Electron configuration | [Ar] 3d¹⁰ 4s² 4p³ |
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| Electrons per shell | 2, 8, 18, 5 |
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| Electronegativity (Pauling) | 2.18 |
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| Oxidation states | −3, −2, −1, +1, +2, +3, +4, +5common in bold |
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| State at 25 °C | Solid |
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| Melting point | 1090 K816.85 °C |
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| Boiling point | 887 K613.85 °C |
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| Density | 5.727 g/cm³ |
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Atomic properties
| First ionization energy | 9.789 eV |
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| Electron affinity | 78 kJ/mol |
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| Atomic radius | 139 pm |
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| Covalent radius | 119 pm |
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| Van der Waals radius | 185 pm |
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| Common ions | As³⁻ |
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| Protons, neutrons, electrons | 33, 42, 33 |
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Physical and thermal properties
| Molar volume | 12.95 cm³/mol |
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| Heat of fusion | 27.7 kJ/mol |
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| Heat of vaporization | 32.4 kJ/mol |
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| Specific heat | 328 J/(kg·K) |
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| Thermal conductivity | 50 W/(m·K) |
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| Thermal expansion | 5.6 × 10⁻⁶ K⁻¹ |
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| Mohs hardness | 3.5 |
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| Young’s modulus | 8 GPa |
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| Crystal structure | Simple trigonal |
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| Magnetic type | Diamagnetic |
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Identification and history
| CAS number | 7440-38-2 |
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| Latin name | Arsenicum |
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| Discovered by | Albertus Magnus · 1250 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 75As | 74.921595 | 100 % |
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
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Periodic Table