[Jov4nTh3Yu9o]

I'm having trouble with a problem asking me whether a compound satisfies the octet rule or either too many valence electrons, too few, or an odd number of valence electrons.

The compounds are:      Valence Electrons                            I answered:

AsF₅                                  50                                                Too Many

BeH₂                                  4                                                  Too Few

SeO₂^2-                             16                                                  Blank (didn't know what to put)

PCl₃                                   26                                                  Too Few

PS₃                                     23                                                Odd Number

CCl₃                                    36                                                 Too Many

I input these answers and I am incorrect, I am on my 20th try now. I'm not sure how to answer this.
I know the valence electrons but I'm not too confident on how to arrange the lewis structure bond.
Does anyone know what I'm doing incorrectly?

[Dan]

With the exception of BeH₂, your counting of valence electrons is way off. It would help if you can explain how you are counting them. Remember, only the outer shell is involved in bonding.

I will give you an example, SF₆.

Sulfur has 6 valence electrons.
Fluorine has 7.
There are 6 bonds at the S centre. If you draw a Lewis dot and cross diagram (see below, try it), you will see that each of these 6 electrons shares with a F atom, and each F atom shares on of its electrons with S, to form a covalent bond. In SF₆, each F atom had 7 electrons and shares one more from S to give a total of 8 - so the F atoms satisfy the octet rule. However, S had 6 electrons and shares one more from each of the 6 F atoms to give a total of 12 - the S atom does not satisfy the octet rule.



Have a go yourself with the compounds in the list you posted.

[Jov4nTh3Yu9o]

I'm counting using the p,d, and s blocks.

[Dan]

I'm counting using the p,d, and s blocks.

This is incorrect. See for example: http://en.wikipedia.org/wiki/Valence_electron

Try drawing Lewis diagrams and attempt the question again.

[Jorriss]

One thing you are off on is that you check whether individual atoms in a molecule satisfy the octet rule - not whether the molecule satisfies it.

For example, CCl3. What you need to see is how many electrons does carbon have, not the entire CCl3 molecule.

[Jov4nTh3Yu9o]

I've tried again.

AsF₅ I know this is too many.
BeH₂ Is electron deficient, but I put satisfies.
SeO₂^2- Still not sure, but I think too few.
PCl₃ I know satisfies.
PS₃ I know has Odd valence.
CCl₃ I know has too few.

The website still tells me that I am incorrect. I'm not sure where I'm going wrong.

[Dan]

Do dot and cross diagrams and count the electrons. Post your new electron counts and we will see why you are going wrong.

If you don't show your working I can't see where the problem is.