Metals, non-metals and carbon
Carbon and its compounds
Explain why carbon shares electrons rather than trading them, tell a saturated compound from an unsaturated one, work along a homologous series, and name what soap does to oily dirt.
The earth's crust is a fiftieth of one per cent carbon, and the air three hundredths of one per cent carbon dioxide. From that thin ration come food, clothes, medicine, fuel and the whole of you. The number of carbon compounds chemists have written formulae for runs into the millions — more than the compounds of the other elements put together — and the reason lies in how carbon bonds.
Sharing, not trading
Carbon has four electrons in its outer shell. Taking four more would leave six protons trying to hold ten electrons; giving four away would cost a great deal of energy. So carbon shares instead, a pair of electrons at a time, and each shared pair is a covalent bond. Two more things follow. Carbon bonds to other carbon atoms in chains, branches and rings — catenation — and it has four bonds to spend on any of them.
Worked example
Two molecules have the formula C₄H₁₀ and different structures. What are they called, and how can that happen?
Lay out the four carbon atoms first. There are two ways to do it: four in a line, or three in a line with the fourth hanging off the middle one.
The skeleton is where the choice lives. Once it is fixed, the hydrogens have nowhere else to go.
Try it together
Work along the alkane and alkene families using what the tables give you.
Answer with a bare number each time.
1.The table ends at pentane, C₅H₁₂, and hexane, C₆H₁₄. Heptane is the next one along, with seven carbon atoms. How many hydrogen atoms does it have?
Have a go
Have a go on your own. Two neighbours in a homologous series differ by one CH₂ unit. By how much do their molecular masses differ? Answer with a number.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.