Chemistry · Periodic Classification Of Properties · NEET
When you keep removing electrons from an atom one by one, each ionization enthalpy (IE1, IE2, IE3...) is a bit larger than the one before. The 'big jump' is a sudden very large increase, much bigger than the normal small rise. It happens at one exact place: right after the last valence electron is gone. The next electron then comes from the inner core, which is a complete noble-gas shell held very tightly. NCERT states this directly: 'End of valence electrons is marked by a big jump in ionization enthalpy.'
After you remove an electron, the atom becomes a positive ion. Now the same nucleus (same positive charge) pulls on fewer electrons, so each remaining electron feels a stronger net pull. There is also less electron-electron repulsion. So removing the next electron is harder, and IE2 > IE1, IE3 > IE2, and so on. This is a normal, gradual rise. The big jump is different — it is a sudden extra-large increase, not the usual small one.
Count how many electrons are removed with the normal small rises before the sudden big jump. That count equals the number of valence electrons, which tells you the group. Example: sodium (Na) has one valence electron (3s1). IE1 is small, but IE2 is huge because the second electron comes from the neon core. The jump after the 1st electron shows Na has 1 valence electron, so it is in Group 1. For NEET, this is a fast way to identify the group or block of an element from an ionization energy table.
Two reasons. First, the core is a filled noble-gas shell, which is very stable, so it strongly resists losing an electron. Second, core electrons sit in a lower principal energy level (smaller n), much closer to the nucleus, and feel almost the full nuclear charge with little shielding. A valence electron is far out and well shielded, so it leaves easily. That difference in pull is why the jump is 'big' and not just a normal step.
No. The jump comes after all valence electrons are removed, and that number depends on the group. For Group 1 (like Na, K) the jump is after the 1st electron. For Group 2 (like Mg, Ca) it is after the 2nd. For Group 13 (like Al) it is after the 3rd. So the position of the big jump changes with the group, and that is exactly what makes it useful for identifying the element.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Right after all the valence electrons have been removed. The next electron then comes from the stable inner core (noble-gas shell), causing a sudden large jump.
Only for Group 1 elements like Na. For them the big jump is between IE1 and IE2. For Group 2 it is between IE2 and IE3, and so on, because the jump always comes after the last valence electron.
Because it links electronic configuration, core vs valence electrons, shielding and stability into one idea. NCERT exercise 3.37 uses it, so it is a direct exam-relevant statement.
It tells you the number of valence electrons, which points to the group. Combined with the period, that helps place the element and often its block.
