Ionization energy Trends in the periodic Table

The ionization energy of an atom is the lot of energy required to eliminate an electron indigenous the gaseous type of that atom or ion.

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

For Example:

Na(g) → Na+(g)+ e-I1 = 496 kJ/mol

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

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

For Example:

Na+(g)→ Na2+(g)+ e-I2 = 4560 kJ/mol

The 2nd ionization energy is virtually ten times that of the first because the variety of electrons causing repulsions is reduced.

3rd ionization energy - The energy required to remove a third electron native a doubly charged gaseous 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 rise in magnitude because the variety of electrons, which reason repulsion, stability decrease. This is no a smooth curve there is a huge jump in ionization power after the atom has actually lost its valence electrons. One atom that has actually the same electronic configuration together a noble gas is really going to host on come its electrons. So, the quantity of power needed to remove electrons beyond the valence electrons is considerably greater 보다 the power of chemical reactions and bonding. Thus, just the valence electron (i.e., electrons external of the noble gas core) are affiliated in chemistry reactions.

The ionization energies that a details atom depend on the average electron street from the nucleus and the effective nuclear charge

These determinants can be illustrated by the following trends:


1st ionization energy decreases down a group.

This is due to the fact that the highest energy electrons are, ~ above average, farther indigenous the nucleus. Together the major quantum number increases, the dimension of the orbital increases and also the electron is easier to remove.


I1(Na) > I1(Cs)

I1(Cl) > I1(I)

1st ionization energy increases throughout a period.

This is due to the fact that electrons in the same principal quantum shell execute not completely shield the boosting nuclear charge of the protons. Thus, electrons space held an ext tightly and require much more energy to be ionized.


I1(Cl) > I1(Na)

I1(S) > I1(Mg)

The graph of ionization energy versus atomic number is no a perfect line due to the fact that there room exceptions to the rules that are conveniently explained.


Filled and half-filled subshells display a small increase in stability in the same method that to fill shells show increased stability. So, once trying to remove an electron from among these fill or half-filled subshells, a slightly higher ionization energy is found.

Example 1:


I1(Be) > I1(B)

It"s harder come ionize one electron indigenous beryllium than boron because beryllium has a filled "s" subshell.

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Example 2:


I1(N) > I1(O)

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