Ionization energy Trends in the periodic Table

The ionization energy of one atom is the lot of energy required to eliminate an electron native the gaseous form of that atom or ion.

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1st ionization power - The power required to remove the highest energy electron native a neutral gas atom.

For Example:

Na(g) → Na+(g)+ e-I1 = 496 kJ/mol

Notice the the ionization energy is positive. This is because it requires energy to remove an electron.

2nd ionization energy - The energy required to remove a second electron from a singly fee gaseous cation.

For Example:

Na+(g)→ Na2+(g)+ e-I2 = 4560 kJ/mol

The 2nd ionization energy is almost ten times the of the very first because the variety of electrons leading to repulsions is reduced.

3rd ionization power - The energy required to remove a third electron native a doubly charged gas cation.

For Example:

Na2+(g)→ Na3+(g)+ e-I3 = 6913 kJ/mol

The third ionization energy is even higher than the second.


Successive ionization energies increase in magnitude due to the fact that the number of electrons, which reason repulsion, steadily decrease. This is no a smooth curve there is a big jump in ionization power after the atom has lost that is valence electrons. One atom that has the same digital configuration together a noble gas is really going to hold on come its electrons. So, the quantity of power needed to remove electrons past the valence electron is significantly greater than the power of chemical reactions and also bonding. Thus, just the valence electron (i.e., electrons exterior of the noble gas core) are involved in chemical reactions.

The ionization energies the a certain atom depend on the mean electron distance from the nucleus and also the reliable nuclear charge

These factors can be depicted by the adhering to trends:


1st ionization power decreases down a group.

This is because the highest power electrons are, ~ above average, farther from the nucleus. Together the major quantum number increases, the dimension of the orbit increases and also the electron is simpler to remove.


I1(Na) > I1(Cs)

I1(Cl) > I1(I)

1st ionization energy increases throughout a period.

This is since electrons in the same primary quantum shell perform not totally shield the raising nuclear fee of the protons. Thus, electrons room held much more tightly and also require more energy to it is in ionized.


I1(Cl) > I1(Na)

I1(S) > I1(Mg)

The graph of ionization energy versus atom number is no a perfect line since there room exceptions to the rules the are conveniently explained.


Filled and half-filled subshells show a little increase in stability in the same method that fill shells display increased stability. So, once trying to eliminate an electron from one of these fill or half-filled subshells, a slightly greater ionization energy is found.

Example 1:


I1(Be) > I1(B)

It"s harder to ionize an electron native beryllium than boron because beryllium has actually a fill "s" subshell.

See more: What Characteristic Of A Graph Represents The Rate Of Change ?

Example 2:


I1(N) > I1(O)

Nitrogen has actually a half-filled "2p" subshell so that is harder come ionize one electron indigenous nitrogen 보다 oxygen.