What is Double and triple bonds?

Example 24.7 (Carbon dioxide)

$\ce{CO2}$: $4 + 2 \times 6 = 16$ valence electrons, 8 pairs. Single bonds $\ce{O-C-O}$ use 2 pairs; 6 lone pairs on the oxygens complete them, but carbon then has only 4 electrons. Turning one lone pair of each oxygen into a shared pair gives two double bonds: each atom now has an octet.