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.
It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.
Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and 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.
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.
At standard temperature and pressure, it resists all but the strongest oxidizers.
It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis.
At elevated temperatures, carbon reacts with oxygen to form carbon oxides, and will rob oxygen from metal oxides to leave the elemental metal.
This exothermic reaction is used in the iron and steel industry to smelt iron and to control the carbon content of steel: Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel, and tungsten carbide, widely used as an abrasive and for making hard tips for cutting tools.
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 compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars.