Textbook Notes (363,233)
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Chemistry (65)
Chapter 2

CHEM UA 125- Chapter 2 Notes

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New York University
John Halpin

21matter can be divided into 3 types elements compounds mixturessubstance matter whose composition is fixed elements and compoundselements simplest type of matter with unique physical and chemical propertiesconsists of only one kind of atom cannot be broken downeach element is unique because the properties of its atoms are uniquemolecule independent structure of two or more atoms bound together compound 2 or more different elements that are bonded chemicallythe elements are present in fixed parts by masseach unit of the compound consists of a fixed number of atoms of each elementcan be broken down into simpler substances through chemical changemixture consists of two or more substances that are physically intermingledcomponents of a mixture can vary in their parts by massretains many of the properties of its componentscan be separated by physical changes22Dalton created atomic theory that explained these max lawslaw of mass conservation the goal mass of substances does not change during a chemical reactionnumber of substances and properties may change but amount of mater remains constantmatter cannot be created or destroyedlaw of definite composition no matter what its source a particular compound is composed of the same elements in the same parts by massmass fraction part of the compounds mass that each element contributes mass of each elementmass of compoundlaw of multiple proportions if elements a ad b react to form two compounds the different masses of b that combine with a fixed mass of a can be expressed as a ration of small whole numberssuggests a discrete nature to elementsthe mass fraction of one element relative to the other element changes in increments based on ratios of small whole numbers23Daltons atomic theoryall matter consists of atomsatoms of one element cannot be converted into atoms of another elementatoms of an element are identical in mass and other properties and are different from atoms of any elementcompounds result from the chemical combination of a specific ratio of atoms of different elements24cathode rays rays originating at the negative electrode and moved to the positive electrodecathode rays consist of negatively charged particles found in all mattercathode ray particleselectronsthomson investigated masscharge ratio found that a cathode ray particle weighed less than 11000 of the lightest atomimplies that atoms contain even smaller particlesmillikan measured the charge of the electron oil drop experimenttotal charge of various droplets was always some whole number multiple of a minimum charge
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