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The first ionisation enthalpy values (in...

The first ionisation enthalpy values (in kJ `mol^(-1)`) of group 13 elements are

How would you explain this deviation from the general , trend?

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In accordance to the generaI trend, the ionisation enthalpy decreases on moving down group 13. However, Ga and Tl show exceptional trends.
The shielding effect of d and f electrons is much less pronounced as compared to those of s and p electrons. Ga consists of 3d electrons, whereas Tl possesses 5d and 4f electrons. Due to the poor shielding effect, the valence electrons remain more tightly held by the nucleus in Ga and Tl atoms. This is why they possess slightly higher ionisation enthalpies as compared to their neighbours.
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ICSE-CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES-NCERT TEXT-BOOK. EXERCISE (With Hints and Solutions)
  1. How would you explain the fact that the first ionsiation enthalpy of s...

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  2. What are the various factors due to which the ionization enthalpy of t...

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  3. The first ionisation enthalpy values (in kJ mol^(-1)) of group 13 ele...

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  4. Which of the following pairs of elements would have a more negative el...

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  5. Which of the following pairs of elements would have a more negative el...

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  6. Would you expect the second electron gain enthalpy of O as positive , ...

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  7. What is the basic difference between the terms electron gain enthalpy ...

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  8. How would yon react to the statement that the electronegativity of N o...

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  9. Describe the theory associated with the radius of an atom as it gain...

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  10. Describe the theory associated with the radius of an atom as it lose...

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  11. Would you expect the first ionization enthalpies for two isotopes of t...

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  12. What are the major differences between metals and non-metals?

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  13. Use the periodic table to answer the following questions : Identify ...

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  14. Use the periodic table to answer the following questions : Identify ...

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  15. Use the periodic table to answer the following questions : Identify ...

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  16. Use the periodic table to answer the following questions : Identify...

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  17. The increasing order of reactivity among group 1 elements is Li lt Na ...

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  18. Write the general outer electronic configuration of s-, p-, d- and f- ...

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  19. Assign the position of the element having outer electronic configurati...

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  20. Assign the position of the element having outer electronic configurati...

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