Chem 161-2011 Lecture 3, Ch 2

Chem 161-2011 Lecture 3, Ch 2 - CHEMISTRY 161-2011 LECTURE...

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Chem 161-2011 lecture 3 1 CHEMISTRY 161-2011 LECTURE 3 ANNOUNCEMENTS E-MAIL Don’t let your mailboxes get full. QUIZ/EXAM/WORKSHEET MISCELLANEOUS Bring copy of notes to class Review notes before coming to class. Practice problems coming.
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Chem 161-2011 lecture 3 2 PLAN FOR TODAY : Atom Element Dalton – atom History of the atom Thomson electron Thomson electron charge to mass ratio Millikan’s oil drop experiment (electron charge) Rutherford’s nucleus Chadwick’s neutrons Atomic radiation Isotopes Atomic symbols Mass spectrometry Periodic table Moles, mass and molar mass
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Chem 161-2011 lecture 3 3
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Chem 161-2011 lecture 3 4 Atom (Kimmel’s notes) Atom: The smallest representative particle of an element. If we could arange helium atoms, end-to-end, it would take over 300 million of them to make a line just one millimeter long. Word is from Greek, meaning “unable to be cut” or indivisible. Element: A substance that cannot be separated into simpler substances by chemical means, example gold, oxygen and helium. E.g., C 6 H 12 O 6 can be broken down into C, H and O, but the C, H and O cannot be broken down any further. Atoms proposed by Greek philosophers Democritus, Empedocles about 2500 years ago A philosophical idea, rather than scientific theory. Basically speculative, not based on observation or measurement. Some of the Greek philosophers ascribed shapes to the atoms. Atoms of water: spherical (smooth, flow) Atoms of earth: cubical (rigid, solid) Atoms of fire: jagged (hurts to touch) Modern chemistry and modern atomic theory, relating to scientific observation and measurement, dates back approximately 200 years, to the late 18th and early 19th centuries. John Dalton (1766-1844) proposed several postulates in 1808: Dalton’s postulates can be considered to be interpretations based on scientific measurements and observations. 1. Elements are made of indivisible atoms (actually not true; protons, neutrons, electrons, quarks, etc.) 2. Atoms of each element are the same and different from atoms of other elements. 3. Compounds consist of atoms combining in simple whole number ratios 4. Reactions involve reorganization of the atoms, but no change in the atoms themselves.
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Chem 161-2011 lecture 3 5 Cathode ray tube HISTORY OF STRUCTURE OF THE ATOM o J.J. Thomson (1898-1903) – A cathode ray tube consists of two metal plates sealed inside a tube from which most of the air has been evacuated. Something was emitted from the cathode which was believed to be energy. However, Thomson’s experiments showed that the ray was not energy. Magnetic and electric fields deflect charged particles. Beam of light emanating from a cathode (i.e., a cathode ray) was deflected toward positive magnetic or electric fields, demonstrating that the beam of light was negatively charged particles, i.e., electrons. (Coulomb’s law: Opposite charges attract each other.) These electrons were emitted from all substances,
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Chem 161-2011 Lecture 3, Ch 2 - CHEMISTRY 161-2011 LECTURE...

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