Question

What's the difference between alkanes and alkenes, and what's an example of each?

Answer 1

See below.

Explanation:

Alkenes are saturated hydrocarbons and contain only single bonds. Alkenes are unsaturated hydrocarbons and contain one carbon to carbon double bond.

Alkanes: methane ethane propane

Alkenes: ethenen propene; butene

Answer 2

A very useful expedient in these problems is to assess the the so-called `"degree of unsaturation..."`

Explanation:

An `"saturated organic compound"` has formula `C_nH_(2n+2)`. That is EVERY CARBON atom in the chain has three or two hydrogens. Methane, the simplest alkane, has 4 hydrogens, but higher alkanes fulfil the criterion. Each degree of unsaturation REDUCES the hydrogen count by 2, and corresponds to a RING JUNCTION or an olefinic bond. When oxygen appears in the formula, we assess the degree of unsaturation directly (and of course a degree of unsaturation could correspond to `C=O`). Halogens count for `1*H`; we subtract `NH` from the formula if nitrogen is present.

And thus `HC-=CH` has 2 degrees of unsaturation, it is an alkyne.

And `H_3C-CH_3` has 0 degrees of unsaturation.....an alkane.

And `H_2C=CH_2` has 1 degree of unsaturation.....an olefin, or alkene.

And `H_3C-CH_2NH_2-=C_2H_6`...no degrees of unsaturation.

And `C_3H_8` has 0 degrees of unsaturation.....an alkane.

So to your answer your question....an alkane has the maximum number of hydrogens, and is saturated with respect to hydrogen content....`CH_4`, `C_2H_6`, `C_3H_8`, `C_4H_10`...

And alkenes or olefins have ONE degree of unsaturation given the presence of the `C=C` bond .. consider, ethylene, propylene etc. `H_2C=CH_2`, `H_3C-CH=CH_2`....