ARSENIC
NITROGEN GROUP
| Atomic number: | 33 |
| Group numbers: | 15 |
| Period: | 4 |
| Electronic configuration: | [Ar] 3d10 4s2 4p3 |
| Formal oxidation number: | -3 +3 +5 |
| Electronegativities: | 2.18 |
| Atomic radius / pm: | 124.5 |
| Relative atomic mass: | 74.921 595(6) |
Arsenic was discovered by Albertus Magnus (DE) in 1250. The origin of the name comes from the Greek word arsenikon meaning yellow orpiment. It is a steel-grey, brittle semi-metal that resists water, acids and alkalis. It tarnishes in air, burns in oxygen and is highly toxic by inhalation or ingestion. Arsenic is found in mispickel (arsenopyrite). Many of its compounds are deadly poison and used as weed killer and rat poison. Some compounds, called arsenides, are used in the manufacture of paints, wallpapers and ceramics. It is also used in semiconductors The price of 99.5 % pure arsenic sponge is 322.60 € for 100 g.
| Density / g dm-3: | 5780 | (alpha, 293 K) |
| 4700 | (beta, 293 K) | |
| Molar volume / cm3mol-1: | 12.96 | (alpha, 293 K) |
| 15.94 | (beta, 293 K) | |
| Electrical resistivity / µΩcm: | 33.3 | (20 °C) |
| Thermal conductivity / W m-1K-1: | 50 |
| Melting point / °C: | 817 |
| Boiling point / °C: | 614 |
| Heat of fusion / kJ mol-1: | 27.7 |
| Heat of vaporization / kJ mol-1: | 31.9 |
| Heat of atomization / kJ mol-1: | 301.42 |
| First ionization energy / kJ mol-1: | 944.46 |
| Second ionization energy / kJ mol-1: | 1797.82 |
| Third ionization energy / kJ mol-1: | 2735.48 |
| in the atmosphere / ppm: | - |
| in the Earth's crust / ppm: | 1 |
| in the oceans / ppm: | 0.003 |
| Crystal structure: | rhombohedral |
| Unit-cell dimensions / pm: | a=413.18, α=54°10' |
| Space group: | R3m |
| Isotope | Relative atomic mass | Mass percent (%) |
|---|---|---|
| 75As | 74.921596(2) | 100 |
| Balanced half-reaction | Eo / V | |
|---|---|---|
| H3AsO4 + 3H+ + 2e- → AsO+ + 3H2O | +0.55 | |
| H3AsO4 + 2H+ + 2e- → H3AsO3 + H2O | +0.559 | |
| H3AsO4 + 2H+ + 2e- → H3AsO3 + H2O | +0.577 | (1 mol dm-3 HCl) |
| H3AsO4 + 2H+ + 2e- → H3AsO3 + H2O | +0.577 | (1 mol dm-3 HClO4) |
| H2AsO4- + 3H+ + 2e- → H3AsO3 + H2O | +0.666 | |
| HAsO42- + 4H+ + 2e- → H3AsO3 + H2O | +0.881 | |
| HAsO42- + 3H+ + 2e- → H2AsO3- + H2O | +0.609 | |
| AsO43- + 3H2O + 2e- → H2AsO3- + 4OH- | - 0.67 | |
| 2H3AsO4 + 4H+ + 4e- → As2O3(s) + 5H2O | +0.58 | |
| 2H2AsO4- + 6H+ + 4e- → As2O3(s) + 5H2O | +0.687 | |
| 2HAsO42- + 8H+ + 4e- → As2O3(s) + 5H2O | +0.901 | |
| 2AsO43- + 10H+ + 4e- → As2O3(s) + 5H2O | +1.27 | |
| AsO43- + 8H+ + 5e- → As(s) + 4H2O | +0.648 | |
| As2O3(s) + 6H+ + 6e- → 2As(s) + 3H2O | +0.234 | |
| AsO+ + 2H+ + 3e- → As(s) + H2O | +0.254 | |
| H3AsO3 + 3H+ + 3e- → As(s) + 3H2O | +0.248 | |
| H2AsO3- + 4H+ + 3e- → As(s) + 3H2O | +0.429 | |
| H2AsO3- + H2O + 3e- → As(s) + 4OH- | - 0.68 | |
| As(s) + 3H+ + 3e- → AsH3(g) | - 0.608 |
| 32 Germanium | ← | 33 Arsenic | → | 34 Selenium |
Citing this page:
Generalic, Eni. "Arsenic." EniG. Periodic Table of the Elements. KTF-Split, 18 Jan. 2024. Web. {Date of access}. <https://www.periodni.com/as.html>.
