Chemguide: Support for CIE A level Chemistry

Learning outcome 2.3(c)

This statement deals with writing electronic configurations for atoms and ions using s, p, d notation.

Before you go on, you should find and read the statement in your copy of the syllabus.

You have to be able to write the electronic configuration of an atom or one of its ions given the proton number (atomic number) and charge. You can find the proton number from a Periodic Table, of course, and you will either have to know or be told the charge.

You will find how to do this for atoms explained on the page about electronic structures of atoms.

At the bottom of that page, there is a link to a second page which explains how to do it for ions.

Don't go on to this second page until you are sure you understand the first one. The only way of being sure is to practise doing it. Use a Periodic Table to find the proton numbers, and then practise working out the electronic structure for random atoms up to krypton in the Periodic Table, checking your answers against examples given on the first page.

Once you are certain that you can do it for atoms from hydrogen to krypton, try a few examples of bigger atoms in the s and p blocks. Start with iodine and barium so that you can check your answers with the text on the first page. Then try a few more - you will have to use your initiative to find a way of checking them. (Actually, they aren't hard to find from a Google search!)

Once you are sure you can do this, go on and read, and then practise, the second page about the electronic structures of ions. You will have to restrict yourself to ions whose charges you know.


On the page about the electronic structures of ions, you will find a link to a discussion page about the order of filling of the 3d and 4s orbitals. To keep things simple for yourself, I would suggest that you don't follow this link.

The link challenges the accepted view of the order of filling of these orbitals for the d-block elements. At the time of writing (October 2012), this isn't generally taught at this level. CIE will expect you to use the traditional view that 4s orbitals fill before 3d orbitals.

If you don't read that page, you won't get confused by this.

You will find references to this discussion page at various other places on Chemguide. I would suggest that you ignore it on each occasion. For CIE exam purposes, you need to stick to the generally accepted view.

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© Jim Clark 2010 (last modified March 2014)