# How many valence electrons are used to make sigma bonds in the molecule C3H6?

${C}_{3} {H}_{6}$ has $18$ valence electrons, 12 from the C atoms (4 from each) and 6 from the H atoms (1 from each). The Lewis dot structures for both cyclopropane, and propene, are
However, notice that propene has a double bond, which consists of 1 sigma bond and 1 pi bond; this makes the total number of sigma bonds equal to 8. So, for propene, only $8 \cdot 2 = 16$ valence electrons are used for sigma bonds, the remaining 2 are used for the pi bond.