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NIU CHEM 210 - Chemistry Laws and Theories
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CHEM 210 1st Edition Lecture 6Outline of Last Lecture I. The Components of Matter II. Law of Mass ConservationIII. Law of Definite or Constant CompositionIV. Law of Multiple Proportions Outline of Current Lecture V. Dalton’s Atomic TheoryA. Its relatedness to Mass Conservation, Definite Composition and Multiple ProportionsVI. JJ Thompson and the Cathode Ray TubeVII. Robert Millikan and the Oil Drop ExperimentVIII. Ernest Rutherford and the Gold Foil ExperimentIX. The Atom TodayA. IsotopesCurrent LectureDalton’s Atomic Theory consists of 4 postulates. The first being that all matter consists of atoms. The second postulate states that atoms of 1 element cannot be converted into atoms of another element. The third postulate states that atoms of an element are identical in mass and other properties, and are different from atoms of any other element. Finally, the fourth postulate states that compounds result from the chemical combination of a specific ratio of atoms of different elements.These postulates helped make up some of the laws in chemistry we have today. The Lawof Conservation of Mass states that atoms cannot be created nor destroyed (postulate 1) or converted into other types of atoms (postulate 2) since every atom has a fixed mass (postulate 3). During a chemical reaction, atoms are combined differently and there is no mass change overall.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.In the Law of Definite Composition, it is mentioned that atoms are combined in compounds in specific ratios (postulate 3) and each atom has a specific mass (postulate 4).The Law of Multiple Proportions states that atoms of an element have the same mass (postulate 3) and atoms are indivisible (postulate 1).Overall, these laws derived from Dalton and his atomic theory.JJ Thompson used a cathode ray tube to discover a charged particle. A cathode ray tube is a tube with electricity that begins with a cathode and travels to the anode. The invisible cathode ray showed it contained mass, and the electric field within the experiment demonstrated that the ray was charged. This led to the discovery of the mass to charge ratio.Robert Millikan used an oil drop experiment to find the charge of an electron. There was less than one percent error with his discovery at the time. Using oil droplets and x-rays andcharging them negatively, he found that the oil droplets fell in the same rate as long as they were not in the electric field. Scientists then used Thompson and Millikan’s findings to discover the mass of an electron.Ernest Rutherford and his Gold Foil Experiment led to the discovery of the atomic nucleus. Rutherford shot a beam of tiny charged alpha particles at gold foil and noticed the particles were deflecting and not going straight through the foil. This showed there was something there which he later discovered would be the nucleus. The atoms today is composed of a nucleus with electrons surrounding it, in its orbital. The nucleus is made up of positively charged protons and neutrons which have no charge. The atom as a whole is electrically neutral, which means that the electrons and protons are the same number.Some elements do however contain isotopes. Isotopes occur when an atom has the same number of proteins and is the same chemically, however it has a different number of neutrons. Examples of this include carbon 12 and carbon 14. You can never change the numberof protons in an element. If you do, then you are referring to another element because no two elements have the same atomic number. Protons (p+) have a (+1) charge and a mass of 1. Neutrons (n0) have no charge and a mass of one, and both protons and neutrons make up the nucleus of an atom.Electrons (e-) have a (-1) charge and a mass of 0, and they are located outside of the nucleus or in the


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NIU CHEM 210 - Chemistry Laws and Theories

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