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The Atom From Philosophical Idea to Scientific Theory The Atom • Foundation of the Atomic Theory • The transformation of a substance or substances into one or more new substances is known as a chemical reaction The Atom • Foundation of the Atomic Theory • Democritus (460 - 370 BC) » All matter is composed of tiny indestructible units, called atoms » Different kinds of matter are made up of different kinds of atoms The Atom • Foundation of the Atomic Theory • Aristotle (384-322 BC) » Disagreed with Democritus’ atomic theory » Instead believed that matter was made up of a combination of only four elements water, fire, air, earth » This was the belief for 2000 years The Atom Foundation of the Atomic Theory Law of conservation of mass: mass is neither created nor destroyed during ordinary chemical reactions or physical changes MASS reactants = MASS products Atomic Theory August 21 • How may significant figures would the product of 2.467589 and 2.45 have? • How many significant figures does 300.003 have? • What group and period does Gold appear on? Chapter 1 and 2 Test • When you finish, turn in your test in the 1st period shelf. • Pick up a textbook and complete Chapter 3 vocabulary • All PINK words on wall • You may not use glossary Atomic Theory August 22 • How may significant figures would the sum of 2.4689 and 0.4500 have? • How many significant figures does 00.40 have? • What did the law of conservation of mass state? The Atom Foundation of the Atomic Theory Law of definite proportions: a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound Ex: oxygen = 8/9 of the mass of any sample of pure water, while hydrogen = remaining 1/9 of the mass Joseph Proust, 1804 The Atom Foundation of the Atomic Theory Law of multiple proportions: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers CO and CO2 • C:O • 1:1 ratio • 12g to 16g C:O 1: 2 ratio 12 g to 32 g 2 x the ratio oxygen to carbon H2O H2O2 • H:O ____:____ ratio H:O _____:_____ratio ____g : ____ g _____g : _____ g • file:///D:/student/ch03/sec01/vc04/hc603_01 _v04fs.htm The Atom • Dalton’s Atomic Theory • John Dalton FRS (1766 - 1844) » An English chemist, meteorologist and physicist » He is best known for his pioneering work in the development of modern atomic theory, and his research into color blindness The Atom • Foundation of the Atomic Theory • Dalton’s Atomic Theory » All matter is composed of extremely small particles called atoms » Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties » Atoms cannot be subdivided, created, or destroyed The Atom • Foundation of the Atomic Theory • Dalton’s Atomic Theory » Atoms of different elements combine in simple wholenumber ratios to form chemical compounds » In chemical reactions, atoms are combined, separated, or rearranged Modern Atomic Theory Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that: • Atoms are divisible into even smaller particles • A given element can have atoms with different masses Some important concepts remain unchanged • All matter is composed of atoms • Atoms of any one element differ in properties from atoms of another element 2H2 + O2 2H2O • The equation above shows that 2 molecules (made of 4 atoms) of hydrogen and 1 molecule (made of 2 atoms) of oxygen produce 2 molecules of water. The total mass of the product, water, is equal to the sum of the masses of each of the reactants, hydrogen and oxygen. • What parts of Dalton’s atomic theory are illustrated by this reaction? • What law does this reaction illustrate? • If 3 g of element C combine with 8 g of element D to form compound CD, how many grams of D are needed to form compound CD2? Nitrogen and oxygen combine to form several compounds, as shown by the following table. Calculate the ratio of the masses of nitrogen in each of the following: Compound Mass of nitrogen that combines with 1 g oxygen NO 1.70 NO2 0.85 NO4 0.44 NO NO 2 NO 2 NO 4 Which law do these data illustrate? NO NO 4 Compound Mass of nitrogen that combines with 1 g oxygen NO 1.70 NO2 0.85 NO4 0.44 • NO • N:O • 1:1 1.7g :1 g NO2 N:O 1:2 (8.5 x 2)= 1.7 1.7g : 2g Compound Mass of nitrogen that combines with 1 g oxygen NO 1.70 NO2 0.85 NO4 0.44 NO2 N:O 1:2 (2x.85) =1.7 1.7 g : 2 g NO4 N:O 1:4 (.44 x 4) =1.76 1.76 to 4 g August 23 WARM UP: Find the ratio of N :O Compound Mass of nitrogen that combines with 1 g oxygen NO 1.70 NO2 0.85 NO4 0.44 NO NO 4 NO N:O NO4 N:O