# What makes the first 3 alkanes decrease in melting point while after that they rise?

What makes the first 3 alkanes decrease in melting point (m.p.) while after that they rise?

$$\begin{array}{lr} \hline \text{Alkane} & \text{m.p.}/\pu{°C} \\ \hline \text{Methane} & -182 \\ \text{Ethane} & -183 \\ \text{Propane} & -188 \\ \text{Butane} & -138 \\ \text{Pentane} & -130 \\ \text{Hexane} & -95 \\ \text{Heptane} & -91 \\ \text{Octane} & -57 \\ \hline \end{array}$$

• It is packing . After the first terms then molecular surface takes the leading role. Perhaps someone will articulate in a more complete form but the juice is this. – Alchimista Mar 10 '18 at 10:18
• – Mithoron Mar 10 '18 at 15:20