ionization+and+affinity

An tom or ion's ability to hold on to its electron(s), or accept new ones, can be measured by two methods:
 * //ionization energy// is the energy change that occurs when an atom or ion loses an electron.
 * //electron affinity energy// is the energy change that occurs when an atom or ion gains an electron.

These energy changes are measured in kilojoules per mole (kJ/mol).


 * Ionization energy vs. Electronegativity**

As the pull on electrons becomes stronger, it becomes more difficult to remove electrons. This means the ionization energy will increase as electronegativity increases.

Here is a chart of ionization energies; compare it to the trends in electronegativity.



Watch this video showing the trends in IE:

media type="youtube" key="8F9nA4Fg3Rw" height="315" width="420"


 * Multiple Ionizations:**

When a neutral atom loses one electron through oxidation, it is called //first ionization energy//; when it loses a second electron, it is the //second ionization energy//; and so on. Here is an example using aluminum.


 * First ionization: Al --> Al 1+
 * Second ionization: Al 1+ --> A 2+
 * Third ionization: Al 2+ --> Al 3+

This concept also applies to electron affinity energy, as successive electrons are added to an atom or ion.

The octet rule plays an important role in the magnitude of multiple ionization energies. Breaking the octet rule (a stable noble gas configuration) will require much more energy, as seen in the following chart.



For example, look at the orbital notation of sodium:



When sodium undergoes the first ionization, it loses the 3s electron:

This is the orbital notation for the sodium ion. Note that the 2s and 2p orbitals are still full, and now become the outermost shell. Therefore, the sodium ion has the same electronic structure as the noble gas neon.

The term **//isoelectronic//** is used to identify ions that have electron configurations identical to noble gases.

Look at the above chart to see that taking this first electron away from sodium is relatively easy, with an energy of 498 kJ/mol.

Further, if the sodium ion were to lose a second electron, it would have to come from this full 2p orbital. It would be similar to trying to remove an electron from the inert neon atom, which is very difficult to do.

To demonstrate this, the first ionization energy of Ne is high, at 2080 kJ/mol. But the ionization energy of the sodium ion is even higher, at 4560 kJ/mol (sodium has that extra proton, remember).


 * Electron Affinity Energy**

As the pull on electrons becomes stronger, it becomes easier to gain electrons. This means the electron affinity energy will increase as electronegativity increases.

The chart of electron affinity energies looks very much like the chart of ionization energies.



Again, as with ionization energy, there can be **multiple electron affinity energies**.

Take nitrogen for an example: every time it gains one electron, it has an associated EA energy:
 * First affinity energy: N --> N 1-
 * Second affinity energy: N 1- --> N 2-
 * Third affinity energy: N 2- --> N 3-

Here is a video explaining electron affinity energy trends: media type="youtube" key="bPB0xThmpkg" height="315" width="420"

Again, successive electron affinity energies are dependent on the octet rule and orbital stability (half-full orbitals have some stability):