An isolated carbon atom has four valence orbitals: three mutually perpendicular p orbitals, each with a single nodal plane, and one spherically symmetric s orbital. A carbon atom in a typical molecule can be regarded as bonding with four orbitals consisting of weighted sums (termed hybrids) of these s and p orbitals. One common pattern has four equivalent orbitals, each formed by combining the three p orbitals with the s orbital; this is sp3 hybridization. An sp3 carbon atom forms four sigma bonds, usually in a roughly tetrahedral arrangement. Another common pattern has three equivalent orbitals formed by combining two p orbitals with the s orbital; this is termed sp2 hybridization. An sp2 carbon atom forms three roughly coplanar sigma bonds, usually separated by ~120 , and one pi bond (or several fractional pi bonds). If a single p orbital is combined with the s orbital, the result is sp hybridization, forming two sigma bonds and two pi bonds (usually in a straight line). Atoms of other kinds (e.g., N and O) can hybridize in an analogous manner.

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