Carbon: Fizz, Farts and Fatality
In the first part we looked at just the carbon atom and how it formed the two allotrope’s diamond and graphite.
In this article we’ll look at how carbon ‘gets along’ with other elements to form simple molecules.
If you recall from part 1 carbon has four valence electrons. These are the electrons that ‘orbit’ in the outer-most shell of an atom.
Now, it turns out that atoms are like Humans. Lazy buggers. They like to have full stomachs and do nothing! A full stomach for an atom is having eight electrons in its outer-shell. Once an atom has eight electrons it stops bonding with other atoms and becomes stable. If it has less, then it’s looking for a mate. This is called the ‘octet rule’. Carbon has four…
Jekyll And Hyde
Carbon and oxygen combine to make the gasses Carbon Dioxide and Carbon Monoxide.
Fig 1 shows ‘Lewis diagrams’ of carbon dioxide and carbon monoxide. The lines drawn between the oxygen ( O ) and carbon ( C ) atoms are the ‘bonds’. Each line means that two electrons make the bond (one from each atom). Two lines mean four electrons and three lines mean six.
Carbon dioxide is very stable. It doesn’t burn and it is non-toxic. The ‘bubbles’ that we enjoy in beer and sparkling wine are carbon dioxide. It readily dissolves (under pressure) in water. You can see this when you open a bottle of fizzy water and the gas is released due to the lowering of the pressure. Like the dreaded diver’s ‘bends’!
If we count the valence electrons you’ll see why it’s stable. Oxygen has six outer-shell electrons (Fig 1c), carbon has four.
Each oxygen atom needs two more electrons to fulfil the ‘octet rule’. The carbon atom needs four more.
The carbon atom ‘shares’ two of its electrons with each oxygen atom. In return, each oxygen atom ‘shares’ two electrons with the carbon atom. All atoms now have eight electrons satisfying the octet rule and the molecule is therefore stable.
Carbon monoxide is not so friendly, it’s toxic. As you can see from Fig 1b it only has one oxygen atom. This is ‘triple bonded’ to the carbon atom. The octet rule applies only because the oxygen atom is providing an extra electron to the carbon atom.
The carbon atom isn’t a ‘happy-chappy’. He’s looking for another oxygen atom.
Carbon monoxide burns in air with a clear blue flame. As it does so it combines with oxygen to make carbon dioxide. If you’ve ever watched a coal or log fire burn you may have noticed (especially as the fire dies down) a blue flame of carbon monoxide shoot out of a coal or log.
If you ‘starve’ something of oxygen that is burning you make carbon monoxide. This is why it’s not a good idea to have a barbecue indoors!
Humans need oxygen to survive. It’s ‘transported’ around the body via something called haemoglobin. Unfortunately, carbon monoxide can attach itself to haemoglobin just as easily as oxygen. Therefore, if you breathe it you’ll suffocate from the inside.
When coal-gas was being piped to homes for fuel, carbon monoxide poisoning was one of the more ‘popular’ ways of committing suicide.
As the name suggests, are molecules made from carbon and hydrogen atoms. The whole petrochemical industry would not exist but for carbon and hydrogen bonds. Carbon being the key that holds it all together.
Whether it’s the fuels that we burn (such as paraffin or petrol) or the numerous plastics we take for granted, hydrocarbons make the modern world possible.
The simplest hydrocarbon is methane. Four hydrogen atoms held together with a carbon atom. Methane is a gas that burns in oxygen. The decomposition of organic matter produces methane. This makes it a popular ‘bio-fuel’.
Some of us produce methane through flatulence. I say ‘some’ because the most flammable part of our ‘farts’ is actually hydrogen!
Methane is an odourless gas. Our farts smell because of the bacteria in our colon. The childish game of pretending to faint when someone’s farted is interesting from a purely molecular point of view.
If we replace three of the four hydrogen (H) atoms in our methane diagram with chlorine (Cl) atoms we get the anaesthetic chloroform (CHCl3). This is no longer used in anaesthesia as it causes heart arrhythmia. It’s not a gas but a liquid at room temperature.
It can be made very easily from products in your house, although you’d be an idiot to do so. Mixing household bleach and strong alcohol together and then heating them will make some chloroform. Again, DON’T TRY THIS.
One of the most mass produced plastics in the world is polyethylene (or polythene). It’s made from the gas ethylene.
This gas comes from the petrochemical industry. (Crude oil.) It can also be produced from booze!
It’s made up of four hydrogen atoms bonded to two carbon atoms. The two carbon atoms are double bonded to each other.
If we break the double bond between the two carbon atoms we get the plastic polyethylene. (Fig 2)
The way chemists break this bond is with something called a catalyst.
A molecule of ethylene is called a monomer. After we break the double carbon bond we get a polymer. We can see from Fig 2 that each carbon atom now has a free bond.
This bond will ‘stick’ to another molecule of polyethylene, and another and so on. Hence poly meaning ‘many’.
This post is getting long, so I’ll stop here. (Hurrah! I hear you cry.)
We haven’t even touched upon the alcohols or carbohydrates and only just scratched the surface of polymers.
Carbon is one of the ‘holy quaternity’ of atoms that are the basis for organic chemistry. Hydrogen, oxygen and nitrogen being the other three.
I think that we can all agree that carbon is a pretty special atom. Not only is it a key to life but the whole of our synthetic world relies upon it. We would not be straying too far from the truth by saying that carbon ‘physically holds together’ and (literally) conducts the modern world.
So raise a glass of your favourite tipple to Carbon. Cheers!
(PS: My apologies to all the real chemists out there.)
© Dr Mike Finnley