Key Points for Ionization Energy:

Ionization Energy

Students

Basic:

• Ion - An atom or group of atoms which has a net charge, ie, there are not enough electrons to properly balance out the charge of the nuclei. This happens when an electron is added or ejected from the atom.
• Ionization energy is the amount of energy needed to eject an electron from an atom.
• Some atoms have multiple ionization energies when they are able to add or remove more than one electron.
• Ionization energies (IE) increase from bottom to top and from left to right across the periodic table.
• Atomic size increase from top to bottom and from right to left across the periodic table.
• Electron Affinity (EA) - the amount of energy needed to add an electron to an atom.
• IE = EA
• EA = energy of the Lowest Unoccupied Molecular Orbital (LUMO)
• Subtraction Method: IE = Energy of the ion - Energy of the neutral atom

Advanced:

• Frontier Orbitals - a collective term for the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO)
• Frontier Orbitals help calculate electronegativity, hardness, and aromaticity.
• Koopman's Theory: The IE is equal to the HOMO energy (this method is exact for only hydrogenic atoms)