For organic compounds, the length of the C-O bond does not vary widely from 120 picometers. Inorganic carbonyls have shorter C-O distances: CO, 113; CO, 116; and COCl, 116 pm.
The carbonyl carbon is typically electrophilic.  A qualitative order of electrophilicity is RCHO (aldehydes) > RCO (ketones) > RCOR' (esters) > RCONH (amides).   A variety of nucleophiles attack, breaking the carbon-oxygen double bond.
Interactions between carbonyl groups and other substituents were found in a study of collagen. Substituents can affect carbonyl groups by addition or subtraction of electron density by means of a sigma bond. ΔHσ values are much greater when the substituents on the carbonyl group are more electronegative than carbon.
The polarity of C=O bond also enhances the acidity of any adjacent C-H bonds.  Due to the positive charge on carbon and the negative charge on oxygen, carbonyl groups are subject to additions and/or nucleophilic attacks. A variety of nucleophiles attack, breaking the carbon-oxygen double bond, and leading to addition-elimination reactions. Nucleophiliic reactivity is often proportional to the basicity of the nucleophile and as nucleophilicity increases, the stability within a carbonyl compound decreases. The pK values of acetaldehyde and acetone are 16.7 and 19 respectively,