12/16/2019eNotes Print View1/4Student: Rijah KamranCourse Name: OC Chemistry Honors, A, HPLesson Name: The Historical Development of Atomic TheoryDemocritus was the first to propose the existence of atoms.Idea was not considered a scientific theory.No evidence or explanations. Just thought.John Dalton, almost 2,200 before he the Englishman provided us with truly scientific evidence of thetheory of atomJoseph Proust the Frenchman and Dalton used evidence, observation, objective, and investigation.Sample of compound have the same ratio of elements.The law of definite proportions Small, whole numbers make up the ratio of the masses of theelements found in a compound.Proust discovered that each compound contains the same exact proportion of elements of mass.Law of Definite proportions -> Dalton's atomic theoryThese ideas are an explanation of the structure of matter in terms of different combinations of verysmall particles (atoms).Proust had found that tin oxides were either 88.1% tin and 11.9% O/ Or they were 78.7% tin and 21.3%oxygen. These were the only 2 that formed, so he wanted to break it apart with heat.Dalton started with 100 g of tin and it reacts with 13.4 g oxygen or 27 g O only. Not with any otheramounts of oxygen. Ratio 2:1 = 27/13.5Each tin atom can combine with one or two O atoms. Not with any other ratios.Dalton discovered the first scientific atomic theory.Matter is made of atoms and it is the smallest compound of matter that can't be broken down intosmaller pieces.Elements are composed of one type of atom that are identical atoms that are unique to eachelement. The rest are different.Compounds are composed of atoms of 2+ elements in fixed proportionsThe proportion (or ratio) of atoms is fixed and the same for all samples of that compound.