Structure of the Atom The Atomic Theory: History up to John Dalton Chemistry Timeline Democritus — Fifth century B.C. - Matter is composed of individual particles called “atomos” Alchemists — 100–1600 A.D. - developed many experimental methods and an extensive body of chemical data during their metaphysical pursuits. Chemistry Timeline Joseph Priestley and Antoine–Laurent Lavoisier — 18th century - Demonstrated that combustion is a reaction between matter and oxygen Law of Conservation of Mass - matter can neither be created nor destroyed Chemistry Timeline Joseph Proust — 18th century Law of Definite Proportions - different samples of the same compound always contain its constituent elements in the same proportions by mass Example Proust found that the substance copper carbonate is always 5.3 parts copper 4 parts oxygen 1 part carbon by mass Chemistry Timeline John Dalton — 19th century - Atomic theory Law of Multiple Proportions - if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other elements are in ratios of small whole numbers Example Mass of nitrogen that combines with 1g of oxygen Whole number ratios Compound 1 1.750g = 4 0.4375g Compound 2 0.8750g = 2 0.4375g Compound 3 0.4375g = 1 0.4375g Fundamental Chemical Laws Law of Definite Proportions - different samples of the same compound always contain its constituent elements in the same proportions by mass Law of Multiple Proportions - if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other elements are in ratios of small whole numbers Law of Conservation of Mass - matter can neither be created nor destroyed Dalton’s Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early nineteenth century, championed by John Dalton. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates Each element is composed of extremely small particles called atoms. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. incorporates law of consevation of mass Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. incorporates laws of definite proportions Atoms, and multiple proportions Molecules, and Ions © 2012 Pearson Education, Inc. Atomic Mass relative masses of the atoms determined by comparison to a standard mass.