Ask a Teacher

Search



1.SO3 molecule has zero dipole moment,why? 2.SF6is a known compound but Scl6 and OF6 do not exist,why? 3.H2S is a gas where H2o is a liquid,why? 4.SO2 is a gas but SeO2 is a solid,why? 5.Pcl5 can be an oxidizing agent,not a reducing agent,why? 6.oxygen is a gas but sulphur is a solid,why?
1. SO3 molecule has zero dipole moment,why?
             SO2 has a dipole moment of 1.62D SO3 has a dipole moment of 0. SO3, a trigonal molecule, has no dipole moment beacuse the bond dipoles cancel each other. This is because the negative and positive centres are both loacted in the same place (at the S molecule) as they are all on the same plane and therefore there is no permanant dipole as the dipoles in the bond cancel each other out, therefore the molecule is non polar.

2.SF6 is known while SCl6 is unknown?
         The size of the Cl atom is such that formation of molecules of SCl6 does not occur. As SF6 has the smaller F atoms around the central S atom, this molecule is known. Think about the electron configuration and the effect on the sizes of Cl and F - Cl is in Period 3 and thus has electrons in the third energy level, whereas the electrons in F are in the second. This added energy level is such that 6 Cl atoms cannot 'fit' around one S atom.

Why is OF6 compound not known?
           For the formation of this compound there should be six unpaired electrons in oxygen atom and this is not possible due to absence of 'd' orbitals , secondly the small atomic size of oxygen can not accommodates six fluorine atoms.

3. H2S is a gas where H2o is a liquid,why?
          It is due to the intermolecular forces between the molecules. H2O has stronger forces called hydrogen bonds therefore the mobility of the molecules is limited whereas H2S has a weaker intermolecular force called a dipole to dipole force. The weaker bonds between H2S allow those molecules to break away from each other more easily and thus enter the gas phase (where they are completely mobile and not attracted to each other). Hydrogen bonding will occur between the hydrogens of one molecule and fluorine, oxygen, or nitrogen on adjacent molecules. Since there are no F, O, or N in H2S it can't hydrogen bond.

4.SO2 is a gas but SeO2 is a solid,why?    
   
DIOXIDES OF OXYGEN FAMILY:
Sulfur, selenium and tellurium burn in air to form SO2.SeO2 and TeO2. The dioxide molecules contain p?–p? bonds which become weaker with increase in atomic number because of the increase in the bond length.

         (a) Sulfur dioxide, SO2 is a gas at room temperature and exists as individual molecules even in the solid state. Its molecule has bent structure and is a resonance hybrid of the following canonical structures.

 
           Canonical structures.JPG
 
          SO2 is acidic in nature and also called the anhydride of sulfurous acid. It can act as reducing and oxidizing agent. SO2 also acts as a bleaching agent in the presence of moisture, but in contrast to Cl2, its bleaching action is temporary.
 
              SO2 + 2H2O ————> H2SO4 + 2[H]
       
         Hence, SO2 bleaches due to reduction and the bleaching action is temporary.
 
         (b) Selenium dioxide, SeO2 is a solid with polymeric zig-zag structure at room temperature however it exist as discrete molecules in the gaseous phase.
 
                          gaseous phase.JPG
 
         (c) Tellurium dioxide, TeO2 is also a solid with polymeric zig-zag structure at room temperature very similar to that of selenium dioxide.

5.PCl5 can be an oxidizing agent, not a reducing agent,why?
      Phosphorous in PCl5 exists in +5 oxidation state. 
Reducing agent are the agent which reduces the other species and itself undergoes oxidation. As P is already present in its highest oxidation state and hence can not undergoes further oxidation therefore, PCl5 does not acts as a reducing agent.

6. Oxygen is a gas but sulphur is a solid,why?
             Oxygen is smaller in size and as compared to sulphur. Due to its smaller size it effectively form pi-pi  bond and form O2 molecule. Also the intermolecular forces of O2 is weak vanderwaal's force and it can exist as gas. But S cannot exist as S2 , but exists as a puckered structure held together by strong covalent bonds. Hence it is a solid.


comments powered by Disqus