will electronegative elements increase/decrease basicity?

Question

by adding an electronegative to the end of a molecule that can act as a base (donate a proton), will that increase or decrease its basicity?

Answer 1

At first a molecule that donates a proton is an acid, not a base - according to the Broensted-Lowry definition of acids and bases.

Adding an electronegative atom in a molecule of an acid increases the acidity - or, the same decreases the basicity - of the molecule. For example:

Cl-CH2COOH is a stronger acid than CH3COOH

Cl-NH2 is a weaker base than NH3.

Answer 2

In general, electronegative elements, those which take electrons and form negative ions are the acid formers. This would decrease the alkalinity.