# Homework Help: Help me out with electron configuration. :[

1. Jan 16, 2008

### TheLegend

1. The problem statement, all variables and given/known data
What is the atomic number if the electron config is 1s2, 2s2, 2p6, 3s2, 3p4.

2. Relevant equations
How do I solve for electron configurations using a periodic table?

3. The attempt at a solution
I don't really have any, I am studying for a mid-term and this is all stuff I barely understood in the beginning of the year, and... well... Time makes fools of us all.

I'm not asking for a direct answer, in fact, I don't want that. I want to figure out what I'm missing (in terms of information) on how to tell the electron configuration based on either the electron configuration itself --> element or vice-versa.

Any help is very much appreciated. :)

Last edited: Jan 16, 2008
2. Jan 16, 2008

### rocomath

$$1s^2$$

what does 1 tell you? Think orbitals.

What does s tell you? Where would you find the s group?

what does 2 tell you? Think electrons, but which electrons?

3. Jan 16, 2008

### TheLegend

I know as far as to say that 1 is the energy level, s would be the sub-shell (spdf, 1357) and the ^2 would be the number of electrons within the sub shell.

But regardless, I don't know how to use that information and look at a periodic table and say, "That is..."

4. Jan 16, 2008

### MichaelXY

^2 would be the number of electrons within the sub shell.
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Exactly, so consider what info the atomic number gives in terms of electrons.

Lithium has an atomic number of 3, its config is 1s2 2s1, do you see the relationship?