These pages are devoted to the chemistry of the carbonyl group, the reactions of aldehydes and ketones.
In your textbook it is shown that it is the tendency of oxygen to acquire electrons - its ability to carry a negative charge - that is the real cause of the reactivity of the carbonyl group toward nucleophiles.
This property of oxygen also underlies
a second chemical property of carbonyl compounds: the acidity
of hydrogens alpha to the carbonyl group; the conjugate base, the carbanion,
is stabilized by resonance.
These two, apparently unrelated reactions, have a common feature in that a negative charge is accommodated by the oxygen atom.
Next we discuss a number of reactions, based on these two examples: