What are the symbols for all the elements that have..?

Question

the following outer configurations?

a) s^2
b) s^2p^5
c) s^2d^5

I'm not a slacker just expecting answers.. I'm having a lot of trouble with electron configurations because in my previous class, I have not learned it unlike my new class. I'd be nice if someone can provide explanations as well. Thanks in advance..

Answer 1

a. a s^2 configuration indicates that the outer s shell is filled, but there is no further filling in the outer shells AND IN THE NEXT LOWER d SHELL IF THERE IS A LOWER d SHELL. This sounds confusing, but it works.
The elements that meet this criteria would be He, Be, Mg, Ca, Sr and the other group II metals.

b. These are elements that have the outer s and p shells almost filled. These elements are the
halogens (I, Br, Cl, F and some other that no one really cares about).

c. These are elements where the outer s shell has been filled, but the next electrons are going into a lower-d shell. Since there are 5-d orbitals, these are elements where each orbital is half-full.
Such elements would be the ones that correspond to atomic number 25, 43 (which I believe is radioactive), atomic number 77.