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A_-_102_F11_Notes - A)...

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ChE102 Fall 2011 Class Notes ‐ Introduction A‐1 A) Introduction to Chemistry Petrucci et al. , 10 th Edition: 1.4‐1.5, 2.7‐2.8, 3.1‐3.3, 4.1‐4.5 Note that this is not a comprehensive introduction but rather highlights the minimum required background for the course. If any of the information here is not familiar to you, read the sections in the textbook. If you require more assistance, please contact your instructor and/or the TAs. Dalton’s Atomic Theory: An atom is a minute, indivisible particle that is the smallest unit of a chemical element. Atoms are neither created nor destroyed in chemical reactions. For a given element, atoms have the same properties For atoms of different elements, these properties vary Atoms combine in fixed proportions to form compounds Physical VS Chemical Change Physical Change Sample may go from a liquid, to a solid, or to a vapour, or to some combination thereof Chemical make‐up unchanged Chemical Change or Reaction A change in composition occurs Atoms are added to or lost from the initial sample Law of Conservation of Mass The total mass of substances present before a chemical reaction is the same as the total mass after the reaction. Compounds and Molecules A molecule is the smallest unit that has the same proportion of elements as the overall compound For example: a water molecule (H 2 O) is composed of two hydrogen atoms (H) and one oxygen atom (O) Table salt is sodium chloride: Formula NaCl (the ratio of sodium to chlorine is 1:1) but it is not possible to identify a molecule of sodium chloride Law of Constant Composition All samples of a compound have the same proportion by mass of the constituent elements.
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ChE102 Fall 2011 Class Notes ‐ Introduction A‐2 Isotopes All atoms of the same element have the same number of protons, but they may have different numbers of neutrons. Atomic number is what controls most of the properties of the atom For example, chlorine always has 17 protons but it commonly has either 18 or 20 neutrons. Therefore, there are two isotopes of chlorine, both with atomic number 17 but having mass numbers of 35 and 37. Ions Atom is neutral and has the same number of protons (positive charge) as electrons (negative charge) Ion is an atom that has gained electrons (____________ = negative charge) or lost electrons (______________ = positive charge) Therefore, an ion has a charge For example: Chemical Bonding Minimal knowledge required for this course: Elements combine to form compounds by bonding Bonding involves electrons In a covalent bond , one or more atoms share one or more electrons. For example, in one molecule of methane (CH 4 ), one atom of carbon shares electrons with four atoms of hydrogen In an ionic bond , one atom donates one or more electrons to another atom: For example, in sodium chloride the sodium Na donates an electron, becoming Na + The chlorine accepts it, becoming Cl The formula for sodium chloride is NaCl, but it does not exist as a molecule.
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