Question
Define ionization enthalpy. Name the factors on which ionisation enthalpy depends? How does it vary down the group and across a period?
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Answer
i. The energy required to remove an electron from the isolated gaseous atom in its ground state is called ionization enthalpy $(\triangle _iH).$
Ionization enthalpy is the quantitative measure of tendency of an element to lose electron and expressed in $kJ\ mol^{-1}.$
ii. Ionization energy depends on the following factors
iv. Variation of ionization energy across a period: The screening effect is the same while the effective nuclear charge increases across a period. As a result, the outer electron is held more tightly and hence, the ionization enthalpy increases across a period. Therefore, the alkali metal shows the lowest first ionization enthalpy while the inert gas shows the highest first ionization enthalpy across a period.
Note: First ionization enthalpy values of elements of group $1$.
Note: First ionization enthalpy values of elements of period $2.$
Ionization enthalpy is the quantitative measure of tendency of an element to lose electron and expressed in $kJ\ mol^{-1}.$
ii. Ionization energy depends on the following factors
- Size (radius) of an atom
- Nuclear charge
- The shielding or screening effect of inner electrons
- Nature of electronic configuration
iv. Variation of ionization energy across a period: The screening effect is the same while the effective nuclear charge increases across a period. As a result, the outer electron is held more tightly and hence, the ionization enthalpy increases across a period. Therefore, the alkali metal shows the lowest first ionization enthalpy while the inert gas shows the highest first ionization enthalpy across a period.
Note: First ionization enthalpy values of elements of group $1$.
Note: First ionization enthalpy values of elements of period $2.$
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