Perchlorate (ClO4)-

[Yeo Bin Yook 1K]

So this came up in my test and I'm still having a hard time understanding.
When I drew the Lewis Structure, I put the one negative formal charge on the chlorine, thinking that it would be better than putting it on oxygen that makes things less symmetric. However, I got it wrong and the answer said the extra electron should actually be on oxygen.

Why is this so?

[jadam_1E]

A good general rule when calculating formal charge: make the formal charge on the central atom as close as possible to 0. Also, oxygen is more electronegative than cl so it makes sense for cl to have the additional electron.

[Megan Phan 1K]

Chlorine is the central atom, and for central atoms you want the formal charge to be 0. The negative charge should be on the others, especially in this instance O is more electronegative than Cl.

[Riya Shah 4H]

In ClO4- would all four oxygen atoms have a formal charge of -1?

[Christine Chow 4G]

No, I believe 3 of the oxygens bonded to the chlorine are double bonded, so these would have a formal charge of 0. The one oxygen single bonded by chlorine will have a formal charge of -1.

[janeane Kim4G]

Can someone explain why 3 O would be double bonded with the Cl? Is there a way to determine if an element like Cl will/will not follow the octet guideline?

[Christopher Tran 1J]

Finding out the formal charge of the central atom should tell you whether or not the element will follow the octet guideline, given that the element is in Periods 3+.

For example, in ClO4-, three O are double bonded with the Cl so that the Cl has a formal charge of zero. If the three O were single bonded, then Cl would have had a formal charge of 3+, which is not a favorable structure.

[Kristy 1F]

Since the -1 charge should be on more electronegative atom. And the oxygen atom is more electronegative.