by Ron Kurtus (4 May 2003)
Chemical compounds that are a combination of Hydrogen (H) and Carbon (C) atoms are called hydrocarbons.
Because of the number of electrons in the outer shells or orbits of these two elements, there are a very large number of compounds that can be formed. For example, most petroleum chemicals are hydrocarbons.
Questions you may have include:
- How many electrons are in the outer orbits?
- What type of bonding holds the atoms together?
- What type of molecules can be formed?
This lesson will answer those questions.
Hydrogen has one electron in its outer orbit. That means it tends to combine with other elements so that it will fill its outer orbit with two electrons.
Outer orbit of Hydrogen atom has one electron
Carbon has 2 electrons in the first orbit and 4 electrons in second, outer orbit. It would need four more to fill the orbit with the maximum of 8 electrons.
Outer orbit of Carbon has 4 electrons
Of course, the Carbon atom is much bigger and the Hydrogen atom. Also, we did not show the inner orbit of the Carbon atom, which has two electrons.
One form of chemical bonding is when two atoms share a single electron. The H2 molecule is an example of this. Another form of chemical bonding is when two atoms share each other's electrons, as seen in the illustration below.
Hydrogen and Carbon share each other's electrons
In the example above, Hydrogen now has a full outer orbit, while Carbon still is 3 short of filling its outer orbit. In reality, the outer orbit of Carbon is much bigger than the outer orbit of Hydrogen. They are drawn the same size for the sake of convenience.
If we continue to add Hydrogen atoms, we can fill Carbon's outer orbit too.
The outer orbits of both Hydrogen and Carbon are filled in the resulting compound Methane, which is a volatile gas, which can be explosive.
More complex molecules
Now, two Carbon atoms can also share electrons.
Carbon atoms share electrons
As you can see, each Carbon atom has 5 electrons is its outer orbit. This means we could add 3 Hydrogen atoms to each to make a new compound.
The 6 Hydrogen atoms and the 2 Carbon atoms combine to form Ethane. This method can be continued to form Propane (C3H8), which is an inflammable liquid. Campers often use Propane in lamps and heaters.
Instead of drawing all the electrons, the above illustration is an easier way of diagramming the compound.
You can continue this process to diagram more complex molecules. There are also other ways that Carbon atoms can combine, thus increasing the possibilities of different molecules even more.
Hydrogen and Carbon atoms can combine to form hydrocarbon molecules. Simple examples are Methane, Ethane and Propane. Highly complex hydrocarbon molecules are possible with these building blocks.
Simplify the complex
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