As I was listening commentary on the Northern Gateway Pipeline and it struck me that an understanding of hydrocarbon chemistry might help with some of the debate. So, here is my attempt at Hydrocarbons 101.
The name hydrocarbon comes presence of both hydrogen and carbon in the molecular structure.
Carbon is a strange element. Sitting in the middle of the main group of the periodic table, it is balanced between anions and cations. It would have to gain for electrons to act as anionic species which is hard to do as electrons repel each other. It would have to lose four electrons to become a cation which is equally hard to do as that creates an overwhelming positive charge.
Instead, carbon shares electrons by forming covalent bonds. Maybe that should be written "co-valent" to emphasize that the bond is formed by the sharing of the valence electrons.
That is, two carbon atoms will share a pair of electrons between them. The same is true for a carbon and a hydrogen atom - they share an electron pair. Covalent bonding is very strong. It is like a good marriage.
In the case of hydrocarbons, the simplest of all compounds is methane. This is a carbon, which has four valence electrons, surrounded by four hydrogen atoms, each with a single valence electron. The result is four covalent bonds. Everything is very stable and the bonds are very strong.
Methane, by itself, is not explosive. It is a simple hydrocarbon that doesn't really interact with other methane molecules. As a consequence and because it is such a small molecule, methane is usually found in gaseous form. It is a large component of natural gas.
Next up the hydrocarbon ladder is ethane which consists of two carbons bonded together and surrounded by six hydrogen atoms. If you think of a single carbon having four available sites for attachment, then this arrangement makes sense as each carbon is using up one of its sites to bind to the other carbon atom.
Ethane is slightly larger than methane and slightly heavier. It still forms a gas and is a component of natural gas but it boils at a higher temperature than methane (-89 C versus -164 C). It also does not yield as much energy per carbon dioxide produced as methane.
One more step up the hydrocarbon ladder gives propane - the gas that is used in propane stoves, barbecues and even cars. It is three carbons and eight hydrogen atoms. The middle carbon holds on to the carbons at the end giving a linear arrangement. Propane is sold as is, but is also a constituent of natural gas and is generated as a byproduct during petroleum refining.
One more step up and we have butane. It is much heavier gas with four carbons and ten hydrogen atoms and a boiling point around 0 C. This makes it useful in butane lighters.
These are the gaseous hydrocarbons. They represent the light fraction of petroleum and all are byproducts of petroleum production and refining. They also occur independently.
Pentane, which has five carbons and twelve hydrogen atoms is too heavy to be a gas at typical room temperatures but has a boiling point of only 36 C. It evaporates on human skin. This is the first of the liquid fraction and is the lightest hydrocarbon that is typically found in gasoline.
Hexane, heptane and octane have six, seven and eight carbon atoms, respectively. They are liquids under most normal circumstances. They are too heavy to boil easily but still light enough to move freely at ambient temperatures.
Indeed, the same can be said for all of the straight chain hydrocarbons until around hexadecane which has sixteen carbons in a row. At this point, the molecules are too long and too heavy to move around much so they start to form waxes and tars. From this point on, hydrocarbons are essentially solids.
However, that is strictly only true if the hydrocarbon is pure. Mix in a few other compounds or create a blend of, say, octane, decane and hexadecane and the combination results in a free-flowing mixture. Gasoline is a blend of both simple hydrocarbons and more complex branched hydrocarbons.
Diesel uses heavier hydrocarbons than gasoline.
It is the blended properties of the mixtures that allow them to flow. In the case of bitumen, it is a really-long-chain hydrocarbon with a few other organic constituents thrown in. Even though it is a mixture in its natural state, it is so heavy that it is essentially a solid or a viscous tar.
Only by blending bitumen with some of the lighter hydrocarbons can one generate a free-flowing form. This is what they call dilbit and is essentially a mixture of really heavy and really light hydrocarbons from which we can make gasoline and other petroleum products.
