C₆₀ and C₇₀
The fullerenes are cage molecules connected entirely from carbon atoms. The atoms are sp²-hybridized and each is therefore connected to three others. The fullerenes contain both five-membered six-membered rings; it is the five-membered rings that are responsible for the curvature. Most of the fullerenes contain 12 five-membered rings. The first to be discovered was C₆₀, which s a perfect sphere. Another common example, C₇₀, is not spherical. Many other examples of fullerenes are known.