大学化学课件CHAPTER2【荐】.pdfVIP

Chapter 2: Atoms and Elements Text sections 2.1 - 2.9 Key Concepts Early evidence and models of atoms Structure of atoms Elements, isotopes and atomic masses Periodic Table Moles and Avogadro’s Number Early Chemical Discoveries Law of Conservation of Mass : The total mass of substances after a chemical reaction is the same as the total mass of substances before the reaction Law of Definite Proportions : A compound always contains exactly the same proportion of elements by mass i.e. for 10 kg of H O we have 1.119 kg H and 8.881kg of O 2 for 27 kg of H2O we have 3.021 kg H and 23.979 kg of O Dalton’s Atomic Theory (1808) • chemical elements composed of minute, indestructible particles (atoms); can be neither destroyed nor created during a chemical rxn. • all atoms of an element are alike in mass and other properties, but atoms of one element are different from those of all other elements • in each compound, different elements combine in a simple numerical ratio. J. Dalton (1766-1844) • e.g. 1 atom of A to 1 of B (compound AB), or 1 atom of A to two of B (AB2) Experimental Evidence of Atoms !! What’s in an atom ? Dalton thought atoms were indestructible - now know that atoms can be divided into subatomic particles. Dalton’s Atom Nuclear Atom Experimental work of Thomson, Millikan, Rutherford, Chadwick A Closer Look at the Nuclear Atom more than 99.9% of atom’s mass (and all +’ve charge) confined in an extremely small volume