The dioxygen and diflourine molecules

Like B2, C2 has been investigated in high-temperature vapors. The dissociation energy is Do = 599 kJ mol the bond distance Re = 124.5 pm. The bond is thus twice as strong and 20% shorter than in B2. C2 contains no unpaired electrons. 

The valence electron configuration is 2sa 2sa 2pn corresponding to a double 7t bond. The Lewis formula C C leads to the prediction of a doubly bonded molecule with no unpaired electrons, but does not tell us that the bonding electrons are all 7t electrons. 

The Lewis structure N N is thus in agreement with all the molecular properties. 

Calculations show that the energy of two Ne atoms placed less than 200 pm apart is higher than the energy at infinite distance Two electrons must now be placed in the antibonding 2paa orbital and their presence more than cancels the bonding effect of the two electrons in the 2pa, orbital the potential energy curve is in fact repulsive for intemuclear distances smaller than 300 pm. 

HOMONUCLEAR DIATOMIC SPECIES OF SECOND-PERIOD ELEMENTS 

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