Group 5: Ionization and Electron Affinity

 IONIZATION

Ionization is when an atom or molecule gains either a positive or negative charge. It can occur in one of two ways: first, when electrons are either gained or lost by a particle; second, when one atom or molecule combines with another atom or molecule that already has a charge. The charged particle itself is called an ion. Ions that are positively charged are called cations, and ions that are negatively charged are called anions. As well, ions made up of one atom are called monatomic ions, and ions made up of multiple atoms are called polyatomic ions.

Ionization often occurs because of the number of electrons a particle has. Particles with paired (even-numbered) electrons are more stable than those with unpaired electrons; atoms with filled electron shells are also more stable than those with only partially-filled shells. When particles collide and interact, electrons from one atom might be pulled to another in order to give it an even number of electrons or to fill one of its electron shells. An atom with an odd number of electrons and only a single electron in its outer shell would tend to give up its electron in such an interaction. Particles charged through ionization tend not to be as stable as those that naturally have their electron shells filled with an equal number of protons and electrons.

 ELECTRON AFFINITY
The electron affinity is a measure of the energy change when an electron is added to a neutral atom to form a negative ion. For example, when a neutral chlorine atom in the gaseous form picks up an electron to form a Cl- ion, it releases an energy of 349 kJ/mol or 3.6 eV/atom. It is said to have an electron affinity of -349 kJ/mol and this large number indicates that it forms a stable negative ion. Small numbers indicate that a less stable negative ion is formed. Groups VIA and VIIA in the periodic table have the largest electron affinities.