34 - Selenium polyatomic nonmetal
Discovered by Jöns Berzelius in 1817
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.
H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
57-71 La-Lu Lanthanides
89-103 Ac-Lr Actinides
| Shell | Electrons | Orbitals |
|---|---|---|
| 1 | 2 | 2 in 1s |
| 2 | 8 | 2 in 2s + 6 in 2p |
| 3 | 18 | 2 in 3s + 6 in 3p + 10 in 3d |
| 4 | 6 | 2 in 4s + 4 in 4p |
black, red, and gray (not pictured) allotropes Appearance
79 u Atomic Mass
1.15 Å Atomic Radius
958 K Boiling Point
16 Group
-2, 2, 4, 6 Common Oxidation States
1.2 Å Covalent Radius
4.81 g/cm³ Density
195 kJ/mol Electron Affinity
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 Electron Configuration
[Ar] 3d10 4s2 4p4 Electron Configuration (semantic)
2.55 Electronegativity
34 Electrons
9.75 eV First Ionization Energy
-2, -1, 4, 6 ICSD Oxidation States
941, 2045, 2973.7, 4144, 6590, 7880, 14990 kJ/mol Ionization Energies
494 K Melting Point
93 Mendeleev Number
25.4 J/(mol·K) Molar Heat
4 Number of Shells
6 Electron Valency
45 Neutrons
34 Atomic Number
20 Number of Isotopes
-2, 2, 4, 6 Oxidation States
4 Period
Solid Phase
34 Protons
2, 8, 18, 6 Electron Shell Occupations
0.321 J/(g K) Specific Heat