# Electronic configuration of transition elements

1. Mar 28, 2016

### Docscientist

I know about quantum numbers and how we do it as 1s,2s,2p,3s,3p,3d etc....but how do I find the number of valence electrons by doing this ?
I watched so many videos about this topic and I still don't get it.Possibly because I am trying to learn the portions before even it is taught at school.Can somebody please help me ?
P.S this is not homework.I am just learning things.

2. Mar 28, 2016

### Simon Bridge

It took me a while to get it - most people seem to just memorize the rules.
What education level are you trying this at?

3. Mar 28, 2016

### Docscientist

4. Mar 28, 2016

### Simon Bridge

It's actually a tad above your level... but like I say: because of the statistical nature of QM, the electron bound to an atom is well described as a cloud of charge.
You get ionic bonds where the cloud pokes out a bit to one side and you get covalent bonds when the clouds overlap so they surround both nuclei.
Look up "spherical harmonics".
To get a good picture you need to know about probability.

5. Mar 28, 2016

### Staff: Mentor

Every orbital holds two electrons, yes?

Do you know in what order electrons are placed on the orbitals? It is described by the Aufbau principle (google it, it happens to be quite simple).

Valence electrons are basically those on the latest occupied shell (the one with the highest principle quantum number).

Take any element. Use Aufbau principle to determine its electronic configuration. Count electrons on the latest shell.

6. Mar 28, 2016

### Docscientist

I get it !. Thanks a ton !
And do you any idea why we fill up the p or d orbitals with single electron at first and then once the shells get over,then pair up the electrons by adding one more electron to each shell?
( I assume the shells are the boxes in the picture and orbital is the whole rectangular shape)

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7. Mar 28, 2016

### Staff: Mentor

This is one of these rules you have to accept without any other explanation than "because that's the way it is". Sure, you can show (using advanced QM) that it makes sense, as these are the lowest energy electrons that can be added.

8. Mar 28, 2016

### Docscientist

Thank you,Borek !