Se
Selenium · element 34
Polyatomic Nonmetal · Solid at room temperature
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.
Key facts
Atomic mass
78.9718 u
how heavy one atom is
Phase (room temp.)
Solid
Density
4.81 g/cm³
how tightly packed it is
Melting point
494 K (221 °C)
when solid turns to liquid
Boiling point
958 K (685 °C)
when liquid turns to gas
Period
4
its row in the periodic table
Group
16
its column in the periodic table
Block
P-block
the neighbourhood it lives in
Electronegativity
2.55
how strongly it pulls electrons
Electron configuration
[Ar] 3d10 4s2 4p4
where its electrons live
Shells
2 · 8 · 18 · 6
electrons in each layer, inside to out
Discovered by
Jöns Jakob Berzelius
who found it
Appearance
black, red, and gray (not pictured) allotropes
what it looks like
Source: Wikipedia