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Explain chemical formulas PO43-

  1. Sep 25, 2015 #1
    PO43-

    I Understand the 4 represents how many oxygen atoms are bonded to the Phosphate. What exactly does the 3 and its - sign represent? By the image, I can tell the difference between the 3 oxygen atoms and the single isolated one, with the double || symbol, has a different electronic composition. Explain why the single | symbol is used and why the isolated O atom uses two ||s. Please also describe the difference between the two electronic compositions. Why does it show 3 pairs of dots on the O33-s and a double pair on the single O2-

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  2. jcsd
  3. Sep 25, 2015 #2

    Bystander

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    The superscript indicates the magnitude and charge of ionic species, monatomic or polyatomic.
     
  4. Sep 25, 2015 #3

    dextercioby

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    Have you heard of Lewis structures?
     
  5. Sep 25, 2015 #4

    Merlin3189

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    P has 5 elecrons in outer shell, O has 6 electrons in outer shell. So P + 4O has 5 + 24 = 29 electrons in outer shells
    Dots represent single electrons.
    Bar is a pair of electrons shared
    Double bar is 2 pairs of electrons shared

    Total electrons in diagram = 22 dots + 3 bars + 1 double bar = 22 + 6 + 4 = 32 electrons
    So the ion has 32-29=3 more electrons than the neutral atoms. This is a charge of -3

    As far as I understand it (not very far!) the 3 O each have one extra electron and share an electron with P. Each bar is the sharing of 2 electrons.
    The last O has no extra electons, but shares two from the P.
    Why the P still sees this as only 2 electrons, I don't know, maybe some sort of dative bond? ( I don't really understand hybrid orbitals & all that qed stuff.)
    Phosphorus is funny stuff and appears to exhibit various valencies and bonding combinations. You'll just have to wait for Borek or some other expert to help with that. (Or read about it. There are some pretty detailed explanations I've found, but way over my old head.)
     
  6. Sep 27, 2015 #5

    James Pelezo

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    Have you ever used 'Formal Charge' equation to define the oxidation state of an element in a compound? For PO43-, let the single bonded oxygens be Oxy(1), Oxy(2), Oxy(3) and the double bonded Oxy(4). For Oxys (1 - 3), each has a -1 formal charge... The formal charge equation is FC = V - (B/2) - N; V = valence of element, B = number of bonded electrons, N = number of non-bonded electrons. (Note: B for - O is 2e-, B for = O is 4e- ; N for - O (3 non-bonded pair = 6 electrons) and O (2 non-bonded pair = 4 electrons).

    For PO43-
    Single bonded Oxys ( 1 - 3 ) FC (on each) = V - B/2 - N = 6 - 2/2 - 6 = -1
    Double bonded Oxy ( #4 ) FC = V - B/2 - N = 6 - 4/2 - 6 = 0
    Phosphorous FC = V - B/2 - N = 5 - (10/2) - 0 = 0
    The only elements of the structure carrying a formal charge are the three single bonded oxygens; so ∑ ( - O ) = 3( -1) = -3. Phosphorous and Oxy (4) with double bond FC = 0. => [ (-1) for Oxy#1 ] + [ (-1) for Oxy#2 ] + [ (-1) for Oxy#3 ] + [ (0) for Oxy#4 ] + [ (0) for Phosphorous ] = Net charge for polyion phosphate = -3
     
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