Intro to Hydrocarbons

Hydrocarbons

Organic compounds composed only of carbon and hydrogen atoms.

Properties of Hydrocarbons

The physical properties of hydrocarbons are affected by carbon chain length and molecular polarity.

Alkanes

Saturated hydrocarbons whose molecules are held together by London dispersion forces.

London Dispersion Forces

Temporary intermolecular attractions caused by the constant movement of electrons.

Chain Length

The number of carbon atoms in a hydrocarbon molecule.

Effect of Increasing Chain Length

As the number of carbon atoms increases, molecules become larger, surface area increases, contact between neighboring molecules increases, and intermolecular attractions become stronger.

Why Methane Has a Lower Boiling Point Than Decane

Methane has a much shorter carbon chain and weaker intermolecular attractions, while decane has a longer carbon chain and stronger intermolecular attractions, resulting in a much higher boiling point.

Short Chain Alkanes

Have weak intermolecular attractions, low boiling points, and are usually gases.

Long Chain Alkanes

Have strong intermolecular attractions, high boiling points, and are usually liquids and eventually solids as the chains become even longer.

Boiling Point Trend

The boiling point of alkanes increases as the carbon chain length increases.

Melting Point Trend

The melting point of alkanes generally increases as the carbon chain length increases.

Water

A polar substance whose molecules strongly attract one another through hydrogen bonding.

Alkanes and Hydrogen Bonding

Alkanes cannot form hydrogen bonds.

Why Water and Alkanes Do Not Mix

Water molecules are strongly attracted to one another by hydrogen bonding while alkanes are nonpolar and cannot form hydrogen bonds.