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posted by  Soccer Mom on 11/16/2008 2:10:23 AM  |  status: Live  

Formal changes

Course Textbook Chapter Problem
General Chemistry N/A 8 N/A
Question Details:
Phosphoric acid (H3PO4) is used in the production of phosphate fertilizers and is often found in soft drinks (check the labels). In the molecule, phosphorus is at the center, and the hydrogen atoms are attached to the oxygen atoms. Phosphorous acid (H3PO3) differs slightly in that one of the hydrogen atoms is attached to the central phosphorus atom. Select the Lewis electron dot structure of both.
H3PO4

correct check mark

H3PO3

correct check mark

Compare the formal charges on the phosphorus atoms. (Type your answers using the format +1 and -2.)
H3PO4
wrong check mark
H3PO3
wrong check mark
 
 
Soccer Mom
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posted by CHEMNATION! on 11/16/2008 6:49:19 AM  |  status: Live
Asker's Rating: Lifesaver   
Soccer Mom's comment:
"thanks"
Response Details:
In both cases the formal charge on P is zero.
 
FC = # valence electrons on unbonded atom (5) - the number of electrons assigned to the bonded atom (5)
 
P has 3s2 3p3 valence config (just below N).....5 valence electrons
 
In both cases, there are three single bonds (6 electrons total) with P getting half of these electrons (3) and one double bond bond (4 electrons) with P getting half of these electrons (2) There are no lone pairs on P (if there were they would be assigned 100% to the atom)
 
FC = 5 - 5 = 0
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