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Jump to one of the following Lewis structures' parts:   Choose One Introduction to Lewis Structures Part 1- Basics Part 2- Multiple Bonding and Polyatomic Ions Part 3- Resonance Part 4- Hypervalency Part 5- Formal Charge I Part 6- Formal Charge II Part 7- Electron Deficiency Part 8- Oxoacids Part 9- Quizzes

An oxoacid (or oxyacid) is an acid composed of hydrogen, oxygen, and another element. One way to recognize an acid from the chemical formula is that it's written as "H-something". It's a standard convention to write the acidic hydrogens in front precisely so the compound can easily be recognized as an acid.

Let's try sulfuric acid, H₂SO₄.

We already know that hydrogen can't be the central atom. Therefore, we're left with deciding between one of the oxygens and the sulfur. And now you've got a few ways to go. One is to guess that it's not oxygen since there are more than one (although, that won't help you with the oxoacid HFO), another would be to use the least electronegative atom which would again point to sulfur (but, this wouldn't work with HFO), and another would be to memorize that oxygen is never the central atom when drawing Lewis structures for oxoacids. I'll let you take your pick...

Now we're faced with another decision. Just how do we distribute the atoms about the central sulfur atom? In every previous example all that was needed was to toss the remaining atoms in some way about the central atom. Not so with oxoacids. It's extremely important to remember that the hydrogens are not attached to the central atom but to the oxygens. As in-

That's pretty much the hard part. Luckily, when you go to satisfy the octet rule for the surrounding atoms, any hydrogens are done once you bond them to the oxygen (since we only need to worry about 2 electrons for hydrogen's octet).

Let's go ahead and go through the entire process of drawing the Lewis structure for sulfuric acid before we move on to another structure. I've modified the rules list once again to account for oxoacids.

Here's a current list of the rules.

Pull up the Periodic Table if you need one.

H2SO4
Your turn- enter your answer in the first box and hit "Verify" to see how you did.
1.	Total number of valence electrons.
2.	Draw the skeleton structure.
3.	Connect the atoms by making bonds.
4.	Satisfy the octet rule for the surrounding atoms.
5.	Satisfy the octet rule for the central atom.

No, it's not a mistake. There's no difference between steps 4 and 5. I put that in there to make sure you trust yourself when writing Lewis structures. Many times, but certainly not all, the central atom's octet is satisfied simply by making bonds with its surrounding atoms.

Let's try H₂CO₃.

H2CO3
Your turn- enter your answer in the first box and hit "Verify" to see how you did.
1.	Total number of valence electrons.
2. Draw the skeleton structure. 3. Connect the atoms by making bonds. 4. Satisfy the octet rule for the surrounding atoms. 5. Satisfy the octet rule for the central atom.