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Ionization Energy

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  • 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


    • 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)
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