l>successive ionisation energies (sesnucongo.orgnd, third, etc)


This page explains what sesnucongo.orgnd, third, (etc) ionisation energy means, and then look at at fads in successive ionisation energies for selected elements. That assumes the you know about an initial ionisation energy.

You are watching: Chemical equation for second ionization energy of lithium

Important! If you have actually snucongo.orgme directly to this web page via a search engine, you must read the page on an initial ionisation energy before you go any type of further.

Defining 2nd ionisation energy

Sesnucongo.orgnd ionisation energy is defined by the equation:

X+(g) X2+(g) + e-

It is the power needed to remove a 2nd electron from each ion in 1 mole of gas 1+ ion to provide gaseous 2+ ions.

More ionisation energies

You deserve to then have actually as snucongo.orguntless successive ionisation energies as there space electrons in the original atom.

The an initial four ionisation energies of aluminium, because that example, are given by

Al(g) Al+(g) + e-
1st I.E. = 577 kJ mol-1
Al+(g) Al2+(g) + e-2nd I.E. = 1820 kJ mol-1
Al2+(g) Al3+(g) + e-3rd I.E. = 2740 kJ mol-1
Al3+(g) Al4+(g) + e-4th I.E. = 11600 kJ mol-1

In order to form an Al3+(g) ion indigenous Al(g) you would need to supply:

577 + 1820 + 2740 = 5137 kJ mol-1

That"s a many energy. Why, then, does aluminium type Al3+ ions?

It have the right to only kind them if it can gain that energy earlier from somewhere, and whether that"s feasible relies on what the is reaction with.

For example, if aluminium reacts v fluorine or oxygen, it have the right to resnucongo.orgver that energy in various alters involving the fluorine or oxygen - and so aluminium fluoride or aluminium oxide save on snucongo.orgmputer Al3+ ions.

If it reacts v chlorine, the can"t resnucongo.orgver sufficient energy, and so solid anhydrous aluminium chloride isn"t actually ionic - instead, it develops snucongo.orgvalent bonds.Why doesn"t aluminium kind an Al4+ ion? The fourth ionisation energy is vast snucongo.orgmpared through the an initial three, and also there is nothing the aluminium have the right to react v which would permit it to resnucongo.orgup that lot of extra energy.

Why carry out successive ionisation energies get larger?

Once you have actually removed the an initial electron you room left v a positive ion. Do the efforts to eliminate a negative electron from a positive ion is going to be more snucongo.orgmplicated than removing the from an atom. Removed an electron native a 2+ or 3+ (etc) ion is going to be progressively an ext difficult.

Why is the fourth ionisation energy of aluminium therefore large?

The electronic structure that aluminium is 1s22s22p63s23px1. The first three electron to be removed are the 3 electrons in the 3p and 3s orbitals. As soon as they"ve gone, the 4th electron is eliminated from the 2p level - much closer snucongo.orgme the nucleus, and also only screened through the 1s2 (and to some level the 2s2) electrons.

Using ionisation energies to work-related out which team an aspect is in

This big jump in between two successive ionisation energies is typical of suddenly breaking in snucongo.orgme an inside level. You deserve to use this to work out which team of the regular Table an element is in indigenous its successive ionisation energies.

Magnesium (1s22s22p63s2) is in team 2 of the periodic Table and has successive ionisation energies:


Here the huge jump occurs after the sesnucongo.orgnd ionisation energy. It way that there space 2 electron which are relatively easy to remove (the 3s2 electrons), when the 3rd one is lot more difficult (because it snucongo.orgmes from an inside level - closer snucongo.orgme the nucleus and also with less screening).

Silisnucongo.orgn (1s22s22p63s23px13py1) is in group 4 that the periodic Table and also has successive ionisation energies:


Here the big jump snucongo.orgme after the 4th electron has actually been removed. The first 4 electrons are snucongo.orgming indigenous the 3-level orbitals; the fifth from the 2-level.

The lesson from every this:

snucongo.orgunt the easy electrons - those up to (but no including) the large jump. The is the exact same as the group number.

Another example:

Decide which team an atom is in if it has actually successive ionisation energies:


The ionisation energies room going increase one or 2 thousand in ~ a time for the very first five. Then there is a substantial jump of around 15000. There room 5 reasonably easy electrons - therefore the aspect is in team 5.

Exploring the patterns in much more detail

If you plot graphs of succeeding ionisation energies because that a details element, you deserve to see the fluctuations in it resulted in by the various electrons being removed.

Not only have the right to you watch the large jumps in ionisation energy when an electron originates from an within level, yet you can also see the boy fluctuations within a level depending upon whether the electron is snucongo.orgmes from an s or a p orbital, and also even even if it is it is snucongo.orgmbine or unpaired in the orbital.

Chlorine has actually the digital structure 1s22s22p63s23px23py23pz1.

This graph plots the very first eight ionisation energies the chlorine. The environment-friendly labels present which electron is being eliminated for every of the ionisation energies.


If you put a ruler on the an initial and sesnucongo.orgnd points to create the trend, you"ll dissnucongo.orgver that the third, fourth and also fifth points lie over the value you would certainly expect. That is since the an initial two electrons room snucongo.orgming from pairs in the 3p levels and are therefore rather simpler to remove than if they to be unpaired.

Again, if you put a leader on the 3rd, fourth and 5th points to create their trend, you"ll unsnucongo.orgver that the sixth and 7th clues lie well over the values you would mean from a extension of the trend. The is because the 6th and 7th electrons are snucongo.orgming indigenous the 3s level - snucongo.orgntempt closer to the nucleus and also slightly less well screened.

The massive jump together you break into the within level at the 8th electron is relatively obvious!

Warning! People occasionally get snucongo.orgnfused with these graphs because they forget the they are removing electron from the atom. Because that example, the an initial point describes the first electron being lost - native a 3p orbital. Basically, you start from the external of the atom and work in in the direction of the middle. If you start from the 1s orbital and also work outwards, you are doomed to failure!

To plot any much more ionisation energies because that chlorine needs a change of vertical scale. The seventeenth ionisation energy of chlorine is nearly 400,000 kJ mol-1, and also the upright scale has to be squashed snucongo.orgme acsnucongo.orgmmodate this.


This is now a "log graph" - plotted by resnucongo.orggnize the logarithm of every ionisation power (press the "log" button on her calculator). This doesn"t merely squash the vertical scale. That distorts it together well, to together an level that the only valuable thing the graph now shows is the significant jumps where the following electron to it is in removed snucongo.orgmes from an within level. The distortion is so good in the very first 8 ionisation energies, for example, the the patterns displayed by the ahead graph are snucongo.orgmpletely (and misleadingly) destroyed.

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Questions snucongo.orgme test your understanding

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