Factor 1—What Atom Is the Charge on

The most important factor for determining charge stabihty is to ask what atom the charge is on. For example, consider the two charged compounds below  

The one on the left has a negative charge on oxygen, and the one on the right has the charge on sulfur. How do we compare these We look at the periodic table, and we need to consider two trends comparing atoms in the same row and comparing atoms 

Let s start with comparing atoms in the same row. For example, let s compare carbon and oxygen  

The compound on the left has the charge on carbon, and the compound on the right has the charge on oxygen. Which one is more stable Recall that electronegativity increases as we move to the right on the periodic table  

Since electronegativity is the measure of an element s affinity for electrons (how willing the atom will be to accept a new electron), we can say that a negative charge on oxygen will be more stable than a negative charge on carbon. 

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So we cannot use factor 1 (what atom is the charge on) to determine which proton is more acidic. In both cases, we are dealing with a negative charge on oxygen. But there is a critical difference between these two negative charges. The one on the left is stabilized by resonance ... 

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