We've already looked at the structure of PCl 3.
In fact, it doesn't. A non-existent compound - NCl 5 Nitrogen is in the same Group of the Periodic Table as phosphorus, and you might expect it to form a similar range of compounds.
You might have expected it to use the 4s orbital because this is the orbital that fills before the 3d when atoms are being built from scratch. In methane all the carbon-hydrogen bonds are identical, but our electrons are in two different kinds of orbitals.
We are starting with methane because it is the simplest case which illustrates the sort of processes involved. Phosphorus forms two chlorides - PCl 3 and PCl 5. Covalent bonding at A'level Cases where there isn't any difference from the simple view If you stick closely to modern A'level syllabuses, there is little need to move far from the simple GCSE view.
At a simple level like GCSE a lot of importance is attached to the electronic structures of noble gases like neon or argon which have eight electrons in their outer energy levels or two in the case of helium. The atoms could have become ions in previous reactions with other atoms or the atoms may have reacted with each other, transferring the electron s from one to the other. Energy is released whenever a covalent bond is formed.
It starts with a simple picture of the single covalent bond, and then modifies it slightly for A'level purposes. Why then isn't methane CH 2?
If the phosphorus is going to form PCl 5 it has first to generate 5 unpaired electrons. In order to fill its valence shell, sodium has two options:. Why does phosphorus form these extra two bonds? When an electron moves from one atom to another, both atoms become ions. The reason that NCl 5 doesn't exist is that in order to form five bonds, the nitrogen would have to promote one of its 2s electrons. Questions to test your understanding If this is the first set of questions you have done, please read the introductory page before you start.
For example, water is composed of two hydrogen atoms covalently bonded to a single oxygen atom. You may well have been left with the strong impression that when other atoms react, they try to achieve noble gas structures.
A more sophisticated view of covalent bonding The bonding in methane, CH 4. Atoms like sodium, with only one or two electrons in a valence shell that needs eight electrons, are most likely to give up their valence electrons to achieve a stable state.
You might wonder whether all this is worth the bother! You will remember that the dots-and-crossed picture of methane looks like this. Use the BACK button on your browser to return quickly to this point.
You might perhaps wonder why boron doesn't form ionic bonds with fluorine instead. Hybridisation The electrons rearrange themselves again in a process called hybridisation.