In the NO 3 - ion above, experiment shows that all three bonds are the same length. To explain this, the concept of resonance is used. Resonance can be expected when it is possible to draw more than one structure that follows the octet rule. The extent of the polarity depends upon the difference in electronegativity. Electronegativity - the ability of an atom in a molecule to attract shared electrons to itself.
Electronegativity increases across the periodic table from left to right.
It increases going up the periodic table. The bond energy is defined as H when is broken in the gaseous state. Estimation of H from energies. Combine atoms to form new bonds in products. In general, multiple bonds are stronger than single bonds.