Question

The list below shows the ionization energies for elements 50 through 55:

Element 50: 709 kJ/mol Element 53: 1008 kJ/mol

Element 51: 834 kJ/mol Element 54: 1170 kJ/mol

Element 52: 869 kJ/mol Element 55: 376 kJ/mol

a) Explain why the ionization energies increase as you go from element 50 to element 54.

b) Explain why the ionization energy drops dramatically as you go from element 54 to

element 55.

c) Would you expect the ionization energy of element 56 to be lower than 376 kJ/mol,

between 376 and 1170 kJ/mol, or higher than 1170 kJ/mol?

Answer 1

If we move from element 50 to 54 we are moving across the period in increasing order of atomic number and as the atomic number is increasing each new electron is getting added to the atom along with a proton but as the we add proton the attraction between electrons and protons is getting strengthened and thus due to more effective nuclear charge electrons are more tightly bound to the atom and that is why it requires higher energy to remove them from the atom.

This energy drops dramatically from 54 to 55 becuase element 55 is the start of a new period and the electron it add after element 54 gets added to the new shell which is at greater distance from the nucleus thus the attraction of nuclues on this extra electron is not that much in strength and thus it is loosley bound and we can remove it by lesser energy.

Energy of the element is expected to be between 376 and 1170 kJ/mole as it is easier to remove electron from the element 55 than from the element 56 because of lesser net effective charge of 55 compared to 56 but it will be lesser than element 54 as element 54 has very stable noble state configuration and thus it requires very high energy to remove electron from this stable state but that is not the case with element 56.