Atomic number 34
Selenium
Nonmetal
In the real world
Quick facts
- Atomic mass
- 78.971
- Group
- 16
- Period
- 4
- State (STP)
- solid
- Electronegativity
- 2.55
- Common ox. states
- -2, +4, +6
Properties
Electron configuration
[Ar] 3d¹⁰ 4s² 4p⁴
- Ionization energy
- 941.0 kJ/mol
- Electron affinity
- 195.0 kJ/mol
- Melting point
- 494.00 K (220.9 °C)
- Boiling point
- 958.00 K (684.9 °C)
How dangerous is it?
3/5 · Hazardous
A strange element your body needs in tiny traces but that becomes poisonous in larger amounts. Its dust and compounds are toxic and can leave a garlic smell on the breath.
- ToxicImmediate and cumulative
Selenium dust and compounds are poisonous in more than trace amounts and can cause a garlic breath odor as a sign of exposure. (the dust and compounds; a tiny trace is actually a nutrient)
The dust and compounds are handled with ventilation and care to avoid breathing or swallowing them.
How it bonds
Selenium below sulfur: 2 bonds + 2 lone pairs in H₂Se, expanded-octet +4 and +6 in SeO₂ and SeO₃. Essential trace element (selenocysteine in the enzyme glutathione peroxidase) but toxic in larger doses.
