JEE MAIN - Chemistry (2017 - 8th April Morning Slot - No. 13)
Consider the following ionization enthalpies of two elements 'A' and 'B' .
Which of the following statements is correct ?
| Element | Ionization enthalpy (kJ/mol) | ||
|---|---|---|---|
| 1st | 2nd | 3rd | |
| A | 899 | 1757 | 14847 |
| B | 737 | 1450 | 7731 |
Which of the following statements is correct ?
Both ‘A’ and ‘B’ belong to group-1where ‘B’ comes below ‘A’.
Both ‘A’ and ‘B’ belong to group-1 where ‘A’ comes below ‘B’.
Both ‘A’ and ‘B’ belong to group-2 where ‘B’ comes below ‘A’.
Both ‘A’ and ‘B’ belong to group-2 where ‘A’ comes below ‘B’.
Explanation
From the table you can see ionization enthalpy of A is greater than B in all the cases.
So, B comes below A in the group as in a group from top to bottom ionization enthalpy decreases.
After 1st ionization enthalpy each element become cation by removing a electron. In A+ and B+, after removing one electron from each element, effective nuclear charge increases as per-electron attraction increase by the neuclers. So, the removal of next electron will be more difficult, therefore more energy is required for 2nd ionization energy. From the table you can see 2nd ionization energy is more than first ionization energy for both elements.
But you can see 3rd ionization enthalpy is so much higher than 2nd ionization enthalpy. It means after 2nd ionization enthalpy outermost shell is empty and in 3rd ionization enthalpy from a new shell electron is removed, as the new shell is closer to the neucleus so the attraction by the nucleus to the electrons of this shell is more and to remove a electron from this shell you have to provide very high energy, that is why 3rd ionization enthalpy is so high.
If A and B are from group 1 then after 1st ionization enthalpy outermost shell will be empty and 2nd electron will be removed from inner shell, so 2nd ionization will be so high. But from table you can see 2nd ionization energy is around double of 1st ionization energy, it is not so much high than 1st onization energy. So A and B can't be from group 1.
A and B are from group 2 as in group 2 element, outermost shell has 2 electron and after 2nd ionization enthalpy outermost shell will be empty and in 3rd ionization enethalpy, third electron will removed from innershell so 3rd ionization enthalpy will be very high.
So, B comes below A in the group as in a group from top to bottom ionization enthalpy decreases.
After 1st ionization enthalpy each element become cation by removing a electron. In A+ and B+, after removing one electron from each element, effective nuclear charge increases as per-electron attraction increase by the neuclers. So, the removal of next electron will be more difficult, therefore more energy is required for 2nd ionization energy. From the table you can see 2nd ionization energy is more than first ionization energy for both elements.
But you can see 3rd ionization enthalpy is so much higher than 2nd ionization enthalpy. It means after 2nd ionization enthalpy outermost shell is empty and in 3rd ionization enthalpy from a new shell electron is removed, as the new shell is closer to the neucleus so the attraction by the nucleus to the electrons of this shell is more and to remove a electron from this shell you have to provide very high energy, that is why 3rd ionization enthalpy is so high.
If A and B are from group 1 then after 1st ionization enthalpy outermost shell will be empty and 2nd electron will be removed from inner shell, so 2nd ionization will be so high. But from table you can see 2nd ionization energy is around double of 1st ionization energy, it is not so much high than 1st onization energy. So A and B can't be from group 1.
A and B are from group 2 as in group 2 element, outermost shell has 2 electron and after 2nd ionization enthalpy outermost shell will be empty and in 3rd ionization enethalpy, third electron will removed from innershell so 3rd ionization enthalpy will be very high.
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