Chemical Properties of Alkanes

CHEMICAL PROPERTIES OF ALKANES

Alkanes have little opportunity for reactivity because their carbon atoms have their octet of electrons and four covalent bonds with a valence number of 4. This leads to 4 sigma bonds and no pi-bonds around the carbon atom, which are extremely stable. What this means is that, in order to make a reaction occur, heat energy is needed.

Gasoline is a mixture of hydrocarbons that can last for long periods of time. It only combusts with the addition of flame, which provides energy for its breakdown. Because it is a hydrocarbon, it will float above the surface of the water it sits on. Alkanes are nonpolar solvents that are miscible only in other nonpolar solvents. They have weak dipole-dipole bonds with combustion producing mainly carbon dioxide and water. They do not release as much heat when combusted when compared to other hydrocarbons. They can also be referred to as paraffins, with branched-chain alkanes called isoparaffins.

Methane through butane are very flammable gases at standard temperature and pressure (STP). Pentane is an extremely flammable liquid at STP but boils at 36 degrees Celsius. The boiling points increase with increased alkane length. The first alkane that is solid at room temperature is octadecane, which has 18 carbon atoms. Candle wax has between 20 and 25 carbon chains. Polyethylene is an alkane that has infinite length.

All alkanes are virtually inert to acids and bases, having a pKa of greater than 50. This inertness has led to the fact that alkanes remain unchanged in the ground for millions of years. They do undergo redox reactions with halogens and oxygens, so that reactions with oxygen lead to smokeless combustion and halogenation or substitution when mixed with halogens. Free radicals will react with alkanes to create shorter-chain alkanes and branched-chain isomers. Branched alkanes and cycloalkanes have different bond angles from the optimal 109.5 so that there will be increased reactivity and strain on these molecules.