Occurrence

Occurrence

Oxygen is the single most abundant element on Earth. It makes up about 46.6% by mass of the earth's crust, and dry air itself is 20.946% oxygen by volume — the element most of terrestrial chemistry and life depends on.

Sulphur, by contrast, is far less abundant in the crust, present at only about 0.03–0.1%. It occurs combined chiefly as sulphates — gypsum ($CaSO_4 \cdot 2H_2O$), epsom salt ($MgSO_4 \cdot 7H_2O$) and baryte ($BaSO_4$) — and as sulphides such as galena ($PbS$), zinc blende ($ZnS$) and copper pyrites ($CuFeS_2$). Trace amounts appear as hydrogen sulphide around volcanic vents, and sulphur is also a constituent of many organic materials, including eggs, proteins, garlic, onion, mustard, hair and wool.

Selenium and tellurium are found in nature as metal selenides and tellurides, typically occurring alongside sulphide ores. Polonium occurs naturally only as a decay product of thorium and uranium minerals, reflecting its radioactive origin.

Livermorium is entirely synthetic and intensely radioactive. Its symbol is Lv, atomic number 116, atomic mass 292, and electronic configuration $[Rn]5f^{14}6d^{10}7s^27p^4$. Because it has been produced only in minute quantities and decays with a half-life of a mere fraction of a second, very little of its chemistry can actually be studied.

Table 7.6 collects the key atomic and physical properties — and electronic configurations — of the other Group 16 elements (livermorium excluded, given how little is known of it):