Can you explain why you say impolite and not unpolite or impatient instead of unpatient?

Answer 1

Words like impolite and impatient are derived directly from Latin words ( impolitus, impatiens), and in Latin the prefix in-, meaning "not," assimilates to im- or ir- before roots beginning with those letters. The English prefix un- is used with native Germanic roots ( unearthly, unopened) or with borrowed Latin words which did not provide their own negatives in in-, like unnatural or unexpected.