Sulfur’s amazing structure

Does sulfur exhibit allotropy?

Did you re­al­ly think sul­fur was that sim­ple?

Safe­ty pre­cau­tions

At­ten­tion! All ex­per­i­ments are per­formed by pro­fes­sion­als. Do not at­tempt.

Process de­scrip­tion

Sul­fur mol­e­cules and crys­tals can have a va­ri­ety of struc­tures. Sul­fur mol­e­cules can con­tain five atoms (S₅), eight atoms (S₈), or even more. In turn, the same mol­e­cules (for ex­am­ple, S₈), like con­struc­tion toys, can be as­sem­bled in dif­fer­ent ways: de­pend­ing on how they are “stacked,” they’ll cre­ate solids with dif­fer­ent struc­tures. Sol­id sul­fur pow­der con­sists of S₈ mol­e­cules that are fold­ed in a spe­cial way, form­ing so-called rhom­bic sul­fur. When the pow­der is heat­ed, a yel­low liq­uid of the same com­po­si­tion is formed. How­ev­er, ex­cess heat caus­es some of the mol­e­cules to poly­mer­ize, form­ing S₁₆, S₂₄, etc. and cre­at­ing or­ange spots. A met­al pa­per clip quick­ly ab­sorbs the heat, and the sul­fur crys­tal­lizes im­me­di­ate­ly. How­ev­er, the mol­e­cules ar­range them­selves in a dif­fer­ent way to how they start­ed, form­ing so-called mon­o­clin­ic sul­fur. This cre­ates a strong disc with a dark­er yel­low hue than that of the pow­der. The mol­e­cules find this ar­range­ment “in­con­ve­nient,” and re­ar­range over the course of sev­er­al min­utes (sci­en­tists call such struc­tures metastable). This caus­es the disc to bright­en no­tice­ably and be­come so frag­ile that it is easy to break with three fin­gers!

Safe and cool chem­i­cal ex­per­i­ments await you in the MEL Chem­istry sub­scrip­tion!