نص أصلي - انجليزي - The true science of chemistry as we knowit today...

The true science of chemistry as we knowit today began only in the 1600s.Chemists at that time began to find out how chemikals really work.Then they discovered elements which make up all the millions of different substances on Earth.There are only about a hundred of elements,each of them made up of tiny atoms.The atoms of elements are joined together to make different substances.