Sulphur has a rich chemistry with oxygen. Sulphur forms strong double bonds to oxygen, with, in addition to the σ-interaction, both Opπ-Spπ and Opπ-Sdπ interactions occurring. Oxides with sulphur in low oxidation states occur, but have very short lifetimes. These are SO, (SO)2 (which is a square with similar atoms at opposite corners) and S2O (which has the same structure … Read more
Sulphur forms many compounds, in a range of oxidation states, with the halides. Oxygen forms only OF2 and O2F2. The maximum oxidation state of sulphur, +6, is only achieved in combination with F, forming SF6. The sulphur fluorides in lower oxidation states are unstable with respect to formation of SF6 and fluorine. The structures of the fluorides are all … Read more
Sulphur occurs naturally in the elemental form, and is also found in the gases H2S and SO2. Where oxygen occurs as the gas, sulphur is a solid under standard conditions. This is because it does not form S=S double bonds, but forms rings and chains characterized by S-S single bonds. Sulphur rings Sn, (n=6-12,17,20) and chains … Read more
Oxygen has electronic configuration [He]2s22p4, and has common oxidation states -2,-1, and 0. Other members of the group show a tendency for hypervalence, and have oxidation states from +1 to +6, eg. sulphur in SF6. (For a comparison of the chemistries of oxygen and sulphur, click here.) There are two common allotropes of Oxygen: O2 and O3 (Ozone). O2 In its electronic ground state, … Read more
Phosphorus Oxides P4O6 (oxidation state of P is +3) and P4O10 (oxidation state of P is +5) are known: they both have tetrahedral cage structures, the difference being that the terminal cage positions are occupied in P4O10 whereas they are not in P4O6. P4O6: terminal positions of tetrahedron unoccupied P4O10: terminal positions of tetrahedron occupied The oxides of P both … Read more
Group 15 forms binary halides with the elements in two oxidation states: tri-halides with the oxidation state of +3, and penta-halides with the oxidation state of +5. Tri-Halides All MX3 are formed, and they are all volatile and easily hydrolyzed by water. They are generally formed by direct reaction of the elements. Structures: The gaseous molecules have a pyramidal structure (cf. … Read more
Phosphorus occurs in two forms: white phosphorus is made up of pyramidal P4 units, and is very reactive due to the bond strain in the cage (the P-P-P bond angle is 60o), and black phosphorus which is made up of extended layers of trigonal pyramidal coordinated P atoms. Structure of P4 in white phosphorus: The small bond angle in the tetrahedron means … Read more
Element N occurs as gaseous N2 (which is unreactive due to the high energy required to break the strong triple bond), whereas P occurs in many allotropes, including white phosphorus, P4, which all contain P-P single bonds. P4 is very reactive due to the bond strain in the tetrahedral P4 molecule. The decreasing preference for low numbers of multiple bonds … Read more
The binary nitrogen halides are thermodynamically unstable with respect to decomposition to the elements, with the exception of NF3. NF3 has a much lower dipole moment than ammonia, and has no σ-donor properties. This is because F is more electronegative than N, and hence the N lone pair is polarized towards the F atoms (NF3 is Nδ+(Fδ-)3, whereas NH3 is … Read more
Ammonia (NH3): This is the only thermodynamically stable nitrogen hydride. It is prepared by the Haber process: Ammonia has a pyramidal structure, which undergoes rapid inversion (at a rate of 1010 s-1) Ammonia is more soluble in water than any other gas. This is due to the formation of H-bonds between the NH3 and H2O molecules. It dissolves to give a … Read more