`=>` Due to an increase in nuclear charge which accompanies the filling of the inner `color{red}(d)`-orbitals, there is an increase in ionisation enthalpy along each series of the transition elements from left to right. However, many small variations occur.
`=>` Table 8.2 gives the values for the first three ionisation enthalpies of the first row elements.
● These values show that the successive enthalpies of these elements do not increase as steeply as in the main group elements.
● Although, the first ionisation enthalpy increases, the magnitude of the increase in the second and third ionisation enthalpies for the successive elements, in general, is much higher.
`=>` The irregular trend in the first ionisation enthalpy of the `color{red}(3d)` metals, though of little chemical significance, can be accounted for by considering that the removal of one electron alters the relative energies of `color{red}(4s)` and `color{red}(3d)` orbitals. So, the unipositive ions have `d^n` configurations with no `color{red}(4s)` electrons.
● There is thus, a reorganisation energy accompanying ionisation with some gains in exchange energy as the number of electrons increases and from the transference of `color{red}(s)` electrons into `color{red}(d)` orbitals.
`=>` There is the generally expected increasing trend in the values as the effective nuclear charge increases.
● However, the value of `color{red}(Cr)` is lower because of the absence of any change in the `color{red}(d)` configuration and the value for `color{red}(Zn)` higher because it represents an ionisation from the `color{red}(4s)` level.
`=>` The lowest common oxidation state of these metals is `+2`.
● To form the `color{red}(M^(2+))` ions from the gaseous atoms, the sum of the first and second ionisation energies is required in addition to the enthalpy of atomisation for each element.
● The dominant term is the second ionisation enthalpy which shows unusually high values for `color{red}(Cr)` and `color{red}(Cu)` where the `color{red}(d^5)` and `color{red}(d^10)` configurations of the `color{red}(M^+)` ions are disrupted, with considerable loss of exchange energy.
● The value for `color{red}(Zn)` is correspondingly low as the ionisation consists of the removal of an electron which allows the production of the stable `color{red}(d^(10))` configuration.
`=>` The trend in the third ionisation enthalpies is not complicated by the `color{red}(4s)` orbital factor and shows the greater difficulty of removing an electron from the `color{red}(d^5)` (`color{red}(Mn^(2+))`) and `color{red}(d^(10))` (`color{red}(Zn^(2+))`) ions superimposed upon the general increasing trend.
● In general, the third ionisation enthalpies are quite high and there is a marked break between the values for `color{red}(Mn^(2+))` and `color{red}(Fe^(2+))`.
`=>` Also, the high values for copper, nickel and zinc indicate why it is difficult to obtain oxidation state greater than two for these elements.
`=>` Due to an increase in nuclear charge which accompanies the filling of the inner `color{red}(d)`-orbitals, there is an increase in ionisation enthalpy along each series of the transition elements from left to right. However, many small variations occur.
`=>` Table 8.2 gives the values for the first three ionisation enthalpies of the first row elements.
● These values show that the successive enthalpies of these elements do not increase as steeply as in the main group elements.
● Although, the first ionisation enthalpy increases, the magnitude of the increase in the second and third ionisation enthalpies for the successive elements, in general, is much higher.
`=>` The irregular trend in the first ionisation enthalpy of the `color{red}(3d)` metals, though of little chemical significance, can be accounted for by considering that the removal of one electron alters the relative energies of `color{red}(4s)` and `color{red}(3d)` orbitals. So, the unipositive ions have `d^n` configurations with no `color{red}(4s)` electrons.
● There is thus, a reorganisation energy accompanying ionisation with some gains in exchange energy as the number of electrons increases and from the transference of `color{red}(s)` electrons into `color{red}(d)` orbitals.
`=>` There is the generally expected increasing trend in the values as the effective nuclear charge increases.
● However, the value of `color{red}(Cr)` is lower because of the absence of any change in the `color{red}(d)` configuration and the value for `color{red}(Zn)` higher because it represents an ionisation from the `color{red}(4s)` level.
`=>` The lowest common oxidation state of these metals is `+2`.
● To form the `color{red}(M^(2+))` ions from the gaseous atoms, the sum of the first and second ionisation energies is required in addition to the enthalpy of atomisation for each element.
● The dominant term is the second ionisation enthalpy which shows unusually high values for `color{red}(Cr)` and `color{red}(Cu)` where the `color{red}(d^5)` and `color{red}(d^10)` configurations of the `color{red}(M^+)` ions are disrupted, with considerable loss of exchange energy.
● The value for `color{red}(Zn)` is correspondingly low as the ionisation consists of the removal of an electron which allows the production of the stable `color{red}(d^(10))` configuration.
`=>` The trend in the third ionisation enthalpies is not complicated by the `color{red}(4s)` orbital factor and shows the greater difficulty of removing an electron from the `color{red}(d^5)` (`color{red}(Mn^(2+))`) and `color{red}(d^(10))` (`color{red}(Zn^(2+))`) ions superimposed upon the general increasing trend.
● In general, the third ionisation enthalpies are quite high and there is a marked break between the values for `color{red}(Mn^(2+))` and `color{red}(Fe^(2+))`.
`=>` Also, the high values for copper, nickel and zinc indicate why it is difficult to obtain oxidation state greater than two for these elements.