TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Ionization Energy and Electron Affinity
Ionization Energy
- The amount of energy required to remove 1 mol of electrons from 1 mol of gaseous atoms to form 1 mol of unipositive gaseous ions (ions with a 1+ charge).
Ionization Energy increases when...
- there is stronger nuclear charge
- there is a full subshell (therefore the atom is stable)
- there is a half full subshell therefore there is evenly distributed charge in the atom.
Ionization Energy is low when...
- the electron to be removed is spin paired (therefore there is repulsion)
- the electron is far from the nucleus
- When an electron is in the next subshell, Ionization Energy will lower because the outer electron is at a greater distance from the nucleus and there is more shielding from inner subshells.
- When there is a half full subshell in an atom, the first Ionization Energy is high because the atom is stable.
- Ionization Energy has positive values because energy is always required to remove an electron, it is endothermic. Electrons are attracted to the nucleus therefore energy is needed to remove them.
1st Electron Affinity
- 1st Electron Affinity is negative because energy is given out because electrons are attracted to the nucleus by effective nuclear charge. It is exothermic because electrons have to lose energy to occupy a lower energy orbital.
- 2nd electron affinity is always endothermic (positive) because the electron is added to an ion which is already negative therefore it must overcome the repulsion.
- Electron Affinity becomes more exothermic across the period because effective nuclear charge increases across the period therefore the shells of electrons are pulled closer to the nucleus so the electron must lose more energy to move closer to the nucleus.
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