Tag Archive: Allotrope

Jul 23 2012

Pique the Geek 20120722: More on Carbon

Last time we started our series on carbon, and I now expect it to run for four installments.  Amongst many other properties, carbon is unique in having more allotropic forms than any other element.  Also known as allotropes, these are pure elements with radically different properties.  The term is reserved only for elements, the term for compounds being polymorphs.  An allotrope is a subset of a polymorph.

There is also another distinction:  for an element to have an allotrope, it must exist in the same phase.  Thus, solid lead and molten lead (and lead vapor) are not allotropes, but rather different phases of a given element.

Before we concentrate on carbon, let us consider oxygen.  In the gaseous phase, it has two allotropes, O2, normal molecular oxygen, and O3, also called ozone.  For an element as reactive as oxygen, normal molecular oxygen is remarkably nonreactive (wait a few weeks), but ozone is extremely reactive.  But both are just composed of oxygen atoms.