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Unformatted text preview: on 17661844 Dalton 17661844 Law of Multiple Proportions Noted that C and O can form two compounds. The second has twice the amount of oxygen per gram of Carbon as the first. Suggested this observation could be explained if C and O occurred as individual atoms. One compound could be CO and the other CO2 several other formulas could fit this data Similar observations made for other elements Dalton’s Atomic Theory Dalton’s Atomic Theory Each element is made up of atoms Atoms of a given element are identical Atoms from different elements are different Chemical compounds form by combination of a specific ratio of atoms from different elements A given compound has same relative # and type of atoms Chemical rxns involve reorganization of atoms
Combinations of atoms change The atoms themselves do not change Dalton’s Dilemma Dalton’s Dilemma Cannot specify formulas based on weights To write a correct formula you need to know numbers of atoms and their relative weights Water = 8 g oxygen and 1 g hydrogen Formula could be OH where O is 8 x wgt H Formula could be OH2 where O is 16 x wgt H Avogadro 1811 Avogadro 1811 Combines volumes of gasses 2 Volumes H + 1 Volume O = 1 vol. H2O Assumption Equal volumes of gas contain equal numbers of atoms if Temperature and Pressure are same Good Assumption!! – Not accepted for half a century. Modern View of the Atom Modern View of the Atom A sphere with most of the weight concentrated in a central nucleus which is surrounded by lighter, less densely packed electrons nucleus el ect rons Components of the Atom Components of the Atom Nucleus – Can contain two types particles each with same mass Protons – each carries a positive charge Neutrons – each carries no charge – neutral These account for most of the mass of the atom. Electrons – Small negatively charged particles. These contribute negligible mass to Atom. These are responsible for many chemical and physical properties. Elements have no net charge in elemental form # e must equal # protons to balance charge. # of neutrons can vary – usually the same or more than # protons Why are elements different? Why are elements different? Electrons are largely responsible for behavior of an element Atoms from different elements have different #’s of electrons to balance protons Atoms from different elements have different weights Why are elements different? Why are elements different? Hydrogen symbolized H has 1 electron and one proton Helium...
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