why binding energy and melting point lower than cr
Answers
❤ Good morning ❤
Generally the atomization energies of the first row transition series increases with the increase of the number of unpaired d electrons, but Mn does not comply to this rule, and I want to know why, the opposite is expected.
Answer:
[1]Atomization energy is the energy required to convert one mole of the metal into the gaseous atoms.
[2]Now the metal kernels( atoms), in general, being present in the solid state in a definite unit cell structure are held together by strong metal bonds. We need to first break their definite structure and then convert each atom in the gaseous form.
[3]THE MORE THE METAL BOND STRENGTH, THE MORE WILL BE THE ENERGY REQUIRED TO ATOMIZE THEM AND VICE-VERSA.
[4] Again, the metal bond strength, no doubt, depends upon many factors like their crystal structure( unit cell), packing, coordination number( number of the nearest neighbors of a kernel) and above all the number of unpaired electrons relative to the number of vacant orbitals in the valence shell so that electrons are DE LOCALIZED to a large space ( ELECTRON SEA MODEL THEORY).
THE MORE THE DE LOCALIZATION, THE MORE THE STABILITY AND MORE WILL THE STRENGTH OF METALLIC BOND.
[5]No doubt, Mn[ 3d^5 4s^2] contains the maximum number of unpaired electrons ( five), but this configuration has EXTRA STABILITY due to its having HALF FILLED d-sub shell which makes it to have MAXIMUM EXCHANGE ENERGY.
[6]AS A RESULT, 3d ELECTRONS ARE HELD MORE TIGHTLY BY Mn NUCLEUS AND THIS REDUCES THE DELOCALIZATION OF ELECTRONS-