Question

out of Al and Mg which has higher 2nd ionisation Enthalpy.Why??​

Answer 1

Answer:

mg

Explanation:

because mg lose 2 e gain stability like insert gas

Answer 2

Answer:

Al.

Explanation:

I think we can solve this problem step by step by analysing the elemental atoms' electronic configurations, and then going into the same of their mono-positive and bi-positive ions.

Mg = 1s2 2s2 2p6 3s2

Al = 1s2 2s2 2p6 3s2 3p1

After 1st ionisation-

Mg+ = 1s2 2s2 2p6 3s1

Al+ = 1s2 2s2 2p6 3s2

Now when we're talking about the second ionisation enthalpy, we're actually planning to remove an electron from above mono-positive ions of these, i.e. ions obtained after 1st ionisation.

Look at the configurations after 1st ionisation. Mg+ has a half filled s subshell. Thus it can easily eject one more electron at the second ionisation and be totally stable, devoid of partly/half-filled orbitals totally. Thereby less energy will be needed to make Mg+ bi-positive, as it wants to head towards stability.

However, Al has already attained a stable electronic configurations after first ionisation. So it won't really indulge in further donation of electrons. HENCE IF WE REALLY WANT TO TAKE ANOTHER ELECTRON FROM IT FORCEFULLY, WE'LL HAVE TO APPLY MORE FORCE.

Obviously then, more energy is reqd. to ionise Al the second time than Mg.

So, 2nd ionisation entropy of Al > Mg.