chem questions... help?

Question

Alkanes, alkenes, and alkynes are three main families of aliphatic hydrocarbons.

I. What is the general molecular formula for each family?

II. What is the main structural feature of each family?

III. Why does the number of hydrogen atoms in the molecular formula decrease by two as you go from alkanes to alkenes, and then to alkynes?

Answer 1

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1.  Cn-H2n+2, alkanes, where n= no. of carbons, alkanes

Cn=H2n, alkenes

Cn, triple bond, H2n-2, alkynes

2. alkanes have only single bonds, alkynes have one double bond, alkynes have one triple bond.

2. The decrease is due to the bonds being shared between 2 carbons that are no longer used to bond with hydrogens.