In the ethene molecule, the carbon to carbon double bond consists of

  • A. two sigma bonds
  • B. two pi bonds
  • C. one sigma bond formed by sp2 overlap and one pi bond formed by sideways overlap of unhybridised p orbitals
  • D. one ionic and one covalent bond

Explanation

Each carbon uses three sp2 hybrids for sigma bonds to two hydrogens and to the other carbon, and the leftover p orbital on each overlaps sideways above and below the plane to give the pi bond. This is why the molecule is flat and why rotation is blocked. Every multiple bond follows the same pattern of exactly one sigma plus the remainder as pi.

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