For example, graphite is opaque and black while diamond is highly transparent.
Graphite is soft enough to form a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known.
Carbon forms a vast number of compounds, more than any other element, with almost ten million compounds described to date, The allotropes of carbon include graphite, one of the softest known substances, and diamond, the hardest naturally occurring substance.
It bonds readily with other small atoms including other carbon atoms, and is capable of forming multiple stable covalent bonds with suitable, multivalent atoms.
Its first four ionisation energies, 1086.5, 2352.6, 4620..7 k J/mol, are much higher than those of the heavier group 14 elements.
The electronegativity of carbon is 2.5, significantly higher than the heavier group 14 elements (1.8–1.9), but close to most of the nearby nonmetals as well as some of the second- and third-row transition metals.
All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form.
They are chemically resistant and require high temperature to react even with oxygen.
Carbon's abundance, its unique diversity of organic compounds, and its unusual ability to form polymers at the temperatures commonly encountered on Earth enables this element to serve as a common element of all known life.
Carbon's covalent radii are normally taken as 77.2 pm (C–C), 66.7 pm (C=C) and 60.3 pm (C≡C), although these may vary depending on coordination number and what the carbon is bonded to.
In general, covalent radius decreases with lower coordination number and higher bond order.
For example, graphite can be oxidised by hot concentrated nitric acid at standard conditions to mellitic acid, C Carbon sublimes in a carbon arc which has a temperature of about 5,800 K (5,530 °C; 9,980 °F).
Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest melting point metals such as tungsten or rhenium.