I was watching a lecture of chemistry teacher. He gave the following question:
Q Arrange in terms of increasing ionic character: LiF,NaF,KF,RbF,CsF?
My try: I tried two approaches: Approach 1: As F is common to all compounds, therefore its metal that affects the ionic character. As we move down the group as in this case, the shielding effect increases and hence it becomes more easier to abstract an electron from the outermost shell or in other words, Ionization energy decreases as we move down the group, therefore CsF>RbF>KF>NaF>LiF should be the order.
Approach 2: Li, Na, K, Rb, Cs have same electrovalency. As Cs has more larger size, the positive charge intensity on the atom decreases and thus by formula of electrostatic force F=-kq1q2/r^2, the electrostatic force of attraction decreases and thus lattice energy decreases and therefore order is: LiF>NaF>KF>RbF>CsF.
According to me lattice energy should determine ionic character as lattice energy determines ionic bond strength I think and therefore approach 2 should be more legitimate but when I checked the answer, the answer by Approach 1 was correct. Why is it so? Which of the approach is right and which is wrong and why? Is there any other approach?