7th Ed. 2C.3 Part B: Lewis structure

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Julia Lindner 1I
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7th Ed. 2C.3 Part B: Lewis structure

Postby Julia Lindner 1I » Sun Nov 04, 2018 1:33 pm

For the Lewis structure of hydrogen phosphate ion, the solution shows P in the center with three O and one OH attached to it. My question is, why did they put OH together as one atom instead of connecting O and H with a bond? Is this how compounds are normally arranged? How would you know to do this from just looking at the formula (HO4P^-2)?

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Re: 7th Ed. 2C.3 Part B: Lewis structure

Postby Chem_Mod » Sun Nov 04, 2018 10:53 pm

By saying OH, you are implying that there is a bond connecting the oxygen and the hydrogen atom. Because of the way the formula is written, as HO4P^-2, you know that the hydrogen would attach to the oxygen and not the phosphate. Otherwise, the formula would be written as O4PH^-2.

If you want to think of it another way, you can also think of it in terms of formal charge. With H bonded to the O, a double bond can form between another O and P. You are left with two oxygens with negative charges -- which makes sense because of the -2 charge on this ion. If you attached H to the P, then you would be adding more formal charges to the molecule, either having 4 negatively charged oxygens or having a negatively charged phosphate if you introduce double bonds. With this, it only makes sense to attach the O and the H to give the -2 formal charge.

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