Input interpretation
dihydrogen phosphate anion
Lewis structure
Draw the Lewis structure of dihydrogen phosphate anion. Start by drawing the overall structure of the molecule, ignoring potential double and triple bonds: Count the total valence electrons of the hydrogen (n_H, val = 1), oxygen (n_O, val = 6), and phosphorus (n_P, val = 5) atoms, including the net charge: 2 n_H, val + 4 n_O, val + n_P, val - n_charge = 32 Calculate the number of electrons needed to completely fill the valence shells for hydrogen (n_H, full = 2), oxygen (n_O, full = 8), and phosphorus (n_P, full = 8): 2 n_H, full + 4 n_O, full + n_P, full = 44 Subtracting these two numbers shows that 44 - 32 = 12 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 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), 2.20 (hydrogen), 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 atom would result in an equivalent molecule: Answer: | |
General properties
formula | (H_2PO_4)^- net ionic charge | -1 alternate names | dihydrogen tetraoxophosphate | dihydrogen tetraoxidophosphate | dihydrogen phosphate | dihydrogen phosphate(1-)
Other properties
ion class | anions | ionic conjugate bases | oxoanions | polyatomic ions | ionic weak acids
Thermodynamic properties
molar free energy of formation Δ_fG° | aqueous | -1130 kJ/mol (kilojoules per mole) molar heat of formation Δ_fH° | aqueous | -1296 kJ/mol (kilojoules per mole) molar entropy S° | aqueous | 90.4 J/(mol K) (joules per mole kelvin)