Saved Bookmarks
| 1. |
Assign reasons for the following:(i) The enthalpies of atomisation of transition elements are high.(ii) The transition metals and many of their compounds act as good catalysts.(iii) From element to element the actinoid contraction is greater than the lanthanoid contraction(iv) The E° value for the Mn3+/Mn2+ couple is much more positive than for Cr3+/Cr2+(v) Scandium (Z = 21) does not exhibit variable oxidation states and Let it is regarded as transition element. |
|
Answer» (i) The transition elements exhibit high enthalpies of atomisation because they have large number of unpaired electron in their atoms. Due to this they have stronger inter atomic interaction and hence stronger bonding between atoms. (ii) Many transition metals and their compounds acts as catalyst the catalytic activity is due to their ability to exhibit multiple oxidation states, eg. V2O5 in contact process and finely divided iron in Haber process. (iii) The actinoid contraction is similar to lanthanoid contraction. This contraction is due to poor shielding by 5f electrons in the actioids than that by 4f electrons in the lanthanoids. (iv) Much larger third ionisation energy of Mn (where the required change is Cl5 and d4) is mainly responsible for this. This also explains that +3 state of Mn is of little importance. (v) Scandium (Z = 21) has incompletely filled 3d orbitals in the ground state. (3d) Hence, it is considered as a transition element. |
|