Thus energy is required to increase the separation of

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Thus, ENERGY IS REQUIRED TO INCREASE THE SEPARATION OF FORMAL CHARGES OF OPPOSITE SIGN -- the greater the separation, the greater the energy required.
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(i) Thus, a Resonance Structure with a LARGE separation of +1 and -1 formal charges has a HIGHER ENERGY than does a Resonance Structure with a SMALLER separation of +1 and -1 formal charges (ii) As the ENERGY OF A RESONANCE STRUCTURE INCREASES THE CONTRIBUTION WHICH IT MAKES TO THE ACTUAL ELECTRONIC STRUCTURE OF THE MOLECULE OR ION DECREASES It takes more energy to separate +2 and -2 formal charges to a separation r than it does to separate +1 and -1 formal charges to the same distance r. (iii) Thus, other things being equal, Resonance Structures with a given separation of formal charges of OPPOSITE SIGN AND LARGE MAGNITUDE make smaller contributions to the actual electronic structure than do Resonance Structures with the same separation of formal charges of OPPOSITE SIGN AND SMALL MAGNITUDE. (iv) Resonance Structures with ZERO FORMAL CHARGE on ALL atoms make more important contributions than Resonance Structures with Formal Charge Separation. Energy is REQUIRED to DECREASE the separation of formal charges of the SAME SIGN - the SMALLER the separation, the GREATER is the energy required. (v) Thus, a Resonance Structure with a SMALL separation of +1 and +1 formal charges has a higher energy than a Resonance Structure with a LARGER separation of +1 and +1 formal charges. (vi) Other things being equal, Resonance Structures which place a NEGATIVE formal charge, on ELECTRONEGATIVE atoms and/or a POSITIVE formal charge on ELECTROPOSITIVE atoms are PREFERRED over those Resonance Structures which place a NEGATIVE formal charge on ELECTROPOSITIVE atoms and/or a POSITIVE formal charge on ELECTRONEGATIVE atoms.
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