Phosphorus is very reactive and, therefore, never found in the native elemental form in the Earth's — Physical Chemistry — Thermodynamics Chemistry Question
Structure of phosphorus compounds
Phosphorus is very reactive and, therefore, never found in the native elemental form in the Earth's Crust. Phosphorus is an essential element for all living organisms. It is the major structural component of bone in the form of calcium phosphate and cell membranes in the form of phospholipids. Furthermore, it is also a component of DNA, RNA, and ATP. All energy production and storage, activation of some enzymes, hormones and cell signaling molecules are dependent on phosphorylated compounds and phosphorylation.
Phosphorus has five valence electrons as nitrogen, but being an element of the third period, it has empty d orbitals available to form compounds up to six coordination number. One allotrope of phosphorus is the white phosphorus which is a waxy solid consisting of tetrahedral P4 molecules. White phosphorus is very reactive and bursts into flame in air to yield the phosphorus(V) oxide P4O10. Its partial oxidation in less oxygen yields the phosphorus(III) oxide P4O6. Disproportionation of white phosphorus in basic solution yields the gaseous phosphine, PH3 and hypophosphite ion, H2PO2 -. Phosphorous acid, H3PO3 and phosphoric acid, H3PO4 can be produced by the reaction of P4O6 or P4O10 with water, respectively. White phosphorus reacts with halogens to yield halides with general formulae PX3 and PX5. Oxidation of PCl3 forms phosphoryl trichloride, POCl3. Reaction of PCl5 with LiF yields LiPF6 which is used as an electrolyte in lithium-ion batteries.
Write balanced equations for the preparation of
i. PH3
ii. PCl3
iii. PCl5
iv. P4O6
v. P4O10
vi. H3PO3
vii. H3PO4
viii. POCl3
ix. LiPF6
Model Answer
i. P4(s) + 3 H2O(l) + 3 OH–(aq) → PH3(g) + 3 H2PO2–(aq)
ii. P4(s) + 6 Cl2(g) → 4 PCl3(l)
iii. P4(s) + 10 Cl2(g) → 4 PCl5(l)
iv. P4(s) + 3 O2(g) → P4O6(s)
v. P4(s) + 5 O2(g) → P4O10(s)
vi. P4O6(s) + 6 H2O(l) → 4 H3PO3(aq)
vii. P4O10(s) + 6 H2O(l) → 4 H3PO4(aq)
viii. 2 PCl3(l) + O2(g) → 2 POCl3 (l)
ix. PCl5(l) + 6 LiF(s) → LiPF6(s) + 5 LiCl(s)
Draw the Lewis structures of the following molecules or ions, including the resonance forms if any.
i. PCl3
ii. PCl5
iii. PO4 3–
iv. POCl3
v. PF6 –
Model Answer
i.
ii.
iii.
iv.
v.
Draw the structures of the phosphorus oxides P4O6 and P4O10, starting with tetrahedral P4 skeleton. Each of six oxygen atom will be bridging two phosphorus atoms on an edge. An additional oxygen atom will be bonded to each phosphorus atom as terminal oxo-group in the case of P4O10.
Model Answer
P4O6
P4O10
Using the VSEPR model (Valence Shell Electron Pair Repulsion) determine the geometry of the following molecules or ions:
i. PCl3
ii. POCl3
iii. PCl5
iv. PF6 –
Model Answer
i. PCl3: Coordination number of P atom is 4 (1 lone pair and 3 bond pairs). Thus, electron pair geometry is tetrahedral. Molecular geometry is trigonal pyramidal.
ii. POCl3: Coordination number of P atom is 4 (4 bond pairs). Thus, both electron pair and molecular geometries are tetrahedral.
iii. PCl5: Coordination number of P atom is 5 (5 bond pairs). Thus, both electron pair and molecular geometries are trigonal bipyramidal.
iv. PF6– : Coordination number of P atom is 6 (6 bond pairs). Thus, both electron pair and molecular geometries are octahedral.
What is the hybridization at phosphorus atom in the following molecules or ions?
i. PCl3
ii. POCl3
iii. PCl5
iv. PF6 –
Model Answer
i. sp3
ii. sp3
iii. dsp3
iv. d2sp3