34Se78.972
Polyatomic Non-Metalp-block
Selenium
Element 34 on the periodic table, symbol Se, group 16, period 4.
Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between those of its periodic table column-adjacent chalcogen elements sulfur and tellurium. It rarely occurs in its elemental state in nature, or as pure ore compounds.
Appearance: black, red, and gray (not pictured) allotropes
Properties
- Atomic Number
- 34
- Atomic Mass
- 78.9718 u
- Group
- 16
- Period
- 4
- Block
- p-block
- Category
- Polyatomic Non-Metal
- State at 25 °C
- Solid
- Melting Point
- 494 K · 220.9 °C
- Boiling Point
- 958 K · 684.9 °C
- Density
- 4.81 g/cm³
- Atomic Radius
- 115 pm
- Electronegativity
- 2.55
- Oxidation States
- -2, +2, +4, +6
- Abundance in Crust
- 0.05 mg/kg
- Discovered
- 1817
- Discovered By
- Jöns Jakob Berzelius
Electron Configuration
[Ar] 3d10 4s2 4p4
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
Ionisation Energies (kJ/mol)
- 1. 941
- 2. 2,045
- 3. 2,973.7
- 4. 4,144
- 5. 6,590
- 6. 7,880
- 7. 14,990
Elements near Selenium
Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.