The 9th century chemist Jbir ibn Hayyn (known as "Geber" in Europe), is considered as "the father of chemistry".He introduced a systematic and experimental approach to scientific research based in the laboratory, in contrast to the ancient Greek and Egyptian alchemists whose works were largely allegorical and often unintelligble. He also invented and named the alembic (al-anbiq), chemically analyzed many chemical substances, composed lapidaries, distinguished between alkalis and acids, and manufactured hundreds of drugs. He also refined the theory of five classical elements into the theory of seven alchemical elements after identifying mercury and sulfur as chemical elements.

Source: wiki//

Why are you asking why ? do you mean to say that he shouldnt be considered as the father of chemistry ? better you tell us ,why shouldnt we ?