# Why is the electronegativity of oxygen GREATER than that of carbon?

Well, basically because oxygen has a larger nuclear charge than carbon: i.e. ${Z}_{\text{oxygen">Z_"carbon}}$, where $Z$ is the atomic number.
And because oxygen has greater nuclear charge than carbon, it tends to polarize the electron density of the $C - O$ bond to give ""^(delta+)C-O^(delta-) or ""^(delta+)C=O^(delta-). These representations can help us to rationalize observed chemical reactivity.