Ionization Energy Trends in the Periodic Table

The ionization power of an atom is the amount of energy required to rerelocate an electron from the gaseous develop of that atom or ion.

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1st ionization power - The power compelled to remove the highest power electron from a neutral gaseous atom.

For Example:

Na(g) → Na+(g)+ e-I1 = 496 kJ/mol

Notice that the ionization power is positive. This is bereason it requires power to remove an electron.

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

For Example:

Na+(g)→ Na2+(g)+ e-I2 = 4560 kJ/mol

The second ionization power is almost ten times that of the first because the number of electrons resulting in repulsions is decreased.

3rd ionization energy - The power compelled to rerelocate a third electron from a doubly charged gaseous cation.

For Example:

Na2+(g)→ Na3+(g)+ e-I3 = 6913 kJ/mol

The 3rd ionization power is also higher than the second.


Successive ionization energies boost in magnitude bereason the variety of electrons, which cause repulsion, steadily decrease. This is not a smooth curve There is a big jump in ionization power after the atom has shed its valence electrons. An atom that has the same electronic configuration as a noble gas is really going to host on to its electrons. So, the amount of power required to remove electrons past the valence electrons is considerably higher than the power of chemical reactions and also bonding. Hence, just the valence electrons (i.e., electrons outside of the noble gas core) are connected in chemical reactions.

The ionization energies of a details atom depend on the average electron distance from the nucleus and the reliable nuclear charge

These factors have the right to be shown by the complying with trends:


1st ionization power decreases dvery own a group.

This is because the highest energy electrons are, on average, farther from the nucleus. As the major quantum number increases, the dimension of the orbital rises and the electron is simpler to rerelocate.


I1(Na) > I1(Cs)

I1(Cl) > I1(I)

1st ionization power increases across a duration.

This is bereason electrons in the exact same principal quantum shell carry out not entirely shield the enhancing nuclear charge of the proloads. Hence, electrons are hosted more tightly and require even more energy to be ionized.


I1(Cl) > I1(Na)

I1(S) > I1(Mg)

The graph of ionization energy versus atomic number is not a perfect line bereason there are exceptions to the rules that are quickly explained.


Filled and half-filled subshells show a small increase in stcapability in the same means that filled shells present boosted stcapacity. So, when trying to remove an electron from one of these filled or half-filled subshells, a slightly higher ionization power is discovered.

Example 1:


I1(Be) > I1(B)

It"s harder to ionize an electron from beryllium than boron bereason beryllium has actually a filled "s" subshell.

See more: Calculate The Oh- From The Results Of Your Titrations, Acids And Bases: Titration Example Problem

Example 2:


I1(N) > I1(O)

Nitrogen has a half-filled "2p" subshell so it is harder to ionize an electron from nitrogen than oxygen.