Rewrite the sentences beginning with the words given, so that they mean the same.

Elements are made up of tiny particles called atoms. The concept of atoms was first proposed by the philosopher Democritus in ancient Greece in 400 B.C. He theorised that a material could be divided in to smaller and smaller particles but eventually it would be impossible to divide the material any further and he called these small indestructible particles atomos a Greek word meaning indivisible.
However it wasn't until the late 18th century and early 19th century that there was any experimental evidence for atoms. Both the Frenchman, Lavoisier, and the Englishman, Dalton, discovered that materials react in definite proportions. This can be explained if matter consists of atoms which react together to form molecules. For example water (H2O) is formed when two hydrogen atoms combine with one oxygen atom to form the molecule H2O. Not all compounds consist of molecules such as H2O. For instance when a metal reacts with a non-metal, charged particles called ions are formed. When one sodium atom (Na) reacts with one chlorine atom (Cl), the ionic compound sodium chloride or common salt, is formed, consisting of positive sodium ions (Na+) and negative chlorine ions (Cl-) .But clearly the rule of definite proportion still applies. Dalton was the first scientist to really believe in atoms and he systematically started measuring the relative weights of the different elements (and hence atoms) leading to the birth of modern chemistry.