Chapter 2 (Lecture 3-4)done - Chapter 2: Atoms, Molecules...

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Chapter 2: Atoms, Molecules and Ions Dalton’s atomic theory 4 postulates explain 3 laws Atomic symbols of elements Structure of atom Rutherford’s nuclear model of atom Atomic number and mass number of elements Nucleus, nuclide and notation/symbol
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2.1 4 Dalton’s postulates (1) An atom, a small particle of matter, retains its identity during chemical reactions. (2) An element, a type of matter, composed of only one kind of atom. (3) A compound is a type of matter composed of atoms of two or more elements, chemically combined in fixed proportions. (4) A chemical reaction is about the rearrangement of the atom. Atoms are not created, destroyed, or broken into smaller particles by any chemical reaction.
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2.1.1 Deductions from Dalton’s Atomic Theory 1. Atomic theory explains : - Difference between an element & a compound (Postulates 2 and 3) 2. Law of conservation of mass (Chapter 1) - Which states that the total mass remains constant during a chemical reaction - Postulate 2 : every atom has a definite mass - Postulate 4 : a chemical reaction only rearranges chemical combinations of atoms
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8 X 2 Y 16 X 8 Y + 1.1
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3 . Law of definite proportion: - Postulate 3 : A compound is a type of matter containing atoms of 2 or more elements in definite proportions ( by mass ) because the atoms have definite mass. Example: 1.00g NaCl contains 0.39 g Na, 0.61 g Cl. 4. Law of Multiple proportions: - when two elements form more than one compound, the masses of one element in these compounds for a mixed mass of the other element are in ratios of small whole numbers [Ebbing and Gammon, 7 th ed., Houghton Mifflin Company]
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2 1.1
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1.1
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J.J. Thomson, measured mass/charge of e - 1.1
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e - charge = -1.60 x 10 -19 C Thomson’s charge/mass of e - = -1.76 x 10 8 C/g e - mass = 9.10 x 10 -28 g Measured mass of e - (1923 Nobel Prize in Physics) 1.1
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(Uranium compound) 1.1
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2.2.1 The Structure of Atom Experiment by Ernest Rutherford. - Ernest Rutherford, British physicist, 1911. Shown a rays consist positively charged particles. Proposed the nuclear model of the atom . - Experiments by Hans Geiger and Ernest Marsden. Bombarded a radiation on thin gold foil (or others) - Using radioactive substances (e.g. U). Most alpha particles past through the metal foil. A few (~1 in 8000) were scattered at large angles. Sometimes deflected and almost backward. When hit the positively charged nucleus
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Rutherford’s model of atom * - Consists of a nucleus - A positively charged center - Has most mass of the atom ( 99.95%#) - Which occupies only a very small portion of the space of the atom with negatively charged electrons move around the nucleus. In an atom, there are three subatomic particles:
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Chapter 2 (Lecture 3-4)done - Chapter 2: Atoms, Molecules...

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