Input interpretation
phosphate anion
Lewis structure
Draw the Lewis structure of phosphate anion. Start by drawing the overall structure of the molecule, ignoring potential double and triple bonds: Count the total valence electrons of the oxygen (n_O, val = 6) and phosphorus (n_P, val = 5) atoms, including the net charge: 4 n_O, val + n_P, val - n_charge = 32 Calculate the number of electrons needed to completely fill the valence shells for oxygen (n_O, full = 8) and phosphorus (n_P, full = 8): 4 n_O, full + n_P, full = 40 Subtracting these two numbers shows that 40 - 32 = 8 bonding electrons are needed. Each bond has two electrons, so we expect that the above diagram has all the necessary bonds. However, to minimize formal charge oxygen wants 2 bonds. Identify the atoms that want additional bonds and the number of electrons remaining on each atom. The net charge has been given to the most electronegative atom, oxygen, in 3 places: In order to minimize their formal charge, atoms with large electronegativities can force atoms with smaller electronegativities on period 3 or higher to expand their valence shells. The electronegativities of the atoms are 2.19 (phosphorus) and 3.44 (oxygen). Because the electronegativity of phosphorus is smaller than the electronegativity of oxygen, expand the valence shell of phosphorus to 5 bonds (the maximum number of bonds it can accomodate). Therefore we add a total of 1 bond to the diagram, noting the formal charges of the atoms. Double bonding phosphorus to the other highlighted oxygen atoms would result in an equivalent molecule: Answer: | |
General properties
formula | (PO_4)^(3-) net ionic charge | -3 alternate names | orthophosphate | tetraoxophosphate | tetraoxidophosphate | phosphate | phosphate(3-)
Ionic radius
thermochemical radius | 238 pm
Units
Other properties
ion class | anions | biomolecule ions | ionic conjugate bases | oxoanions | polyatomic ions common sources of ion | zinc phosphate (2 eq) | yttrium(III) phosphate (1 eq) | sodium phosphate dodecahydrate (1 eq) | trisodium phosphate (1 eq) | silver phosphate (1 eq) | samarium(III) phosphate hydrate (1 eq) | praseodymium(III) phosphate (1 eq) | neodymium(III) phosphate hydrate (1 eq) | magnesium phosphate hydrate (2 eq) | lithium phosphate (1 eq)
Thermodynamic properties
molar free energy of formation Δ_fG° | aqueous | -1019 kJ/mol (kilojoules per mole) molar heat of formation Δ_fH° | aqueous | -1277 kJ/mol (kilojoules per mole) molar entropy S° | aqueous | -220.5 J/(mol K) (joules per mole kelvin)