34 2 · 8 · 18 · 6

Selenium, Se, element 34

Nonmetal· Period 4· Group 16· p-block

Configuration [Ar]3d104s24p4

Atomic weight
78.971Da
Phase
solid
Density
4.809g/cm³
Melting point
493.95K 220.8 °C
Boiling point
958.15K 685 °C
Electronegativity
2.55

Metalloid element, belongs to group 16 of the periodic table. Multiple allotropic forms exist. Chemically resembles sulphur. Discovered in 1817 by Jons J. Berzelius. Description from mendeleev.

Back to the table
The outermost shell: the valence electronsThe inner shellsThe nucleus One bead for each electron, on the ring of its shell, counted from the nucleus out. The rings turn at their own pace; the model is Bohr's picture of the atom, which places electrons in shells but not on true orbits.

Atomic properties

5 of 5 fields have a value for selenium

Atomic weight The standard atomic weight. For an element with no stable isotope, the mass of its longest-lived isotope.
78.971Da
Source: mendeleev
Electron configuration
[Ar]3d104s24p4
Source: mendeleev
Uncertainty of the atomic weight
0.008Da
Source: mendeleev
Electron configuration in full The electron configuration with the noble-gas core written out.
1s22s22p63s23p63d104s24p4
Source: Worked outfrom electron configuration
Electrons in each shell Counted from the electron configuration, from the first shell outward.
2 · 8 · 18 · 6
Source: Worked outfrom electron configuration

Screening of each subshell

Clementi's screening constants: how much of the nucleus's charge the other electrons hide from an electron in each subshell. What is left is the effective nuclear charge it feels.

SubshellScreening σEffective charge Z − σ
1s0.737833.2622
2s9.111624.8884
2p3.934830.0652
3s14.596619.4034
3p15.29518.705
3d15.52318.477
4s24.24249.7576
4p25.71288.2872