The second ionization energies in kJ/mol−1 of some elements of period of 4 are: Ca Sc Ti 1145 1235 1310 V Cr Mn 1365 1592 1509 kJ/mol−1 Account for the trend in values.
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Solution
(20)Ca⟶3p64s2
Ca+⟶3p64s1
Ca2+⟶3p64s0
(21)Sc⟶4s23d1
Sc+⟶4s13d1
Sc2+⟶4s03d1
(22)Ti⟶4s23d2
Ti+⟶4s13d2
Ti2+⟶4s03d2
(23)V⟶4s23d3
V⟶4s13d3
V⟶4s03d3
(24)Cr⟶4s23d5
Cr⟶4s03d5
Cr⟶4s03d4
(25)Mn⟶4s23d5
Mn⟶4s13d5
Mn⟶4s03d5
Cr is having highest second ionisation energy value because it is present in its' extra stable half filled state which requires high amount of energy to remove an e− from stable half-filled state.