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Question
Define ionisation enthalpy. Discuss the factors affecting ionisation enthalpy of the elements and its trends in the periodic table.
Solution
The amount of energy required to remove an electron from the outermost shell of an isolated gaseous atom in its ground state is said to be ionisation enthalpy.
The factors that affect ionization enthalpy of the elements are as follows:
a. Effective nuclear charge with its increase the ionization enthalpy also increases
b. Atomic size with its increase the ionization enthalpy decreases
c. The \[\ce{e- - e-}\] repulsion with its increase the ionization enthalpy decreases
d. Whenever there exists half-filled or completely filled orbital than it lead to increase the ionization enthalpy because it leads to give extra stability to the atom due to symmetry
The ionization enthalpy decreases down the group and increases across the period.
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RELATED QUESTIONS
Energy of an electron in the ground state of the hydrogen atom is –2.18 × 10–18 J. Calculate the ionization enthalpy of atomic hydrogen in terms of J mol–1.
Hint: Apply the idea of mole concept to derive the answer.
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The first ionization enthalpy values (in kJmol–1) of group 13 elements are:-
| B | Al | Ga | In | Tl |
| 801 | 577 | 579 | 558 | 589 |
How would you explain this deviation from the general trend?
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(i) 2
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(iii) 1
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Ionisation enthalpy decrease in a group from top to bottom?
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For the gaseous reaction, \[\ce{K_{(g)} + F_{(g)} -> K^+_{ (g)} + F^-_{ (g)}}\], ΔH was calculated to be 19 kcal/mol under conditions where the cations and anions were prevented by electrostatic separation from combining with each other. The ionisation energy of K is 4.3 eV. The electron affinity of F is ______. (in eV)
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