Homologous Series Flashcards

All 4 cards in this deck

State two features of a homologous series.

They have the same general formula, and neighbouring compounds differ by $CH_2$. (Also: same functional group, similar chemical properties, a trend in physical properties.)

What is the general formula of the alkanes?
e.g. the alkane with 4 carbon atoms

$C_nH_{2n+2}$ — with $n = 4$ this gives $C_4H_{10}$.

Why are butane, $C_4H_{10}$, and pentane, $C_5H_{12}$, neighbouring members of the same homologous series?

They differ by $CH_2$, and they have the same general formula $C_nH_{2n+2}$ (both alkanes).

How does the boiling point change as alkane molecules get longer, and why?

It increases. Longer molecules have stronger intermolecular forces between them, so more energy is needed to overcome these forces.