Chapter 3 - 3.1 Molecules, Compounds and Formulas Molecule:...

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3.1 Molecules, Compounds and Formulas Molecule : smallest identifiable unit into which a pure substance can be divided and still retain the chemical properties of a substance. •2 or more elements are bonded together 2 Al + 3Br 2 Al 2 Br 6 (aluminum bromide) Formulas There is more than one way to write the formula of a complex molecule Molecular formula : Atomic composition of molecule Condensed Formula : Shows how atoms are grouped together Structural Formula: Shows how atoms are attached within a molecule Examples : Ethanol C 2 H 6 O (molecular formula) CH 3 CH 2 OH (condensed formula) Dimethyl Ether C 2 H 6 O (molecular formula) CH 3 OCH 3 (condensed formula)
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Structural formula of ethanol Structural formula of dimethyl ether
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Examples : What is the molecular formula for a molecule of styrene? (Condensed formula is C 6 H 5 CHCH 2 ) a. Count the total # of carbons: 8 b. Count the total # of H: 8 Therefore the molecular formula is C 8 H 8 Example : What is the molecular formula for the acrylonitrile molecule? (condensed formula is CH 2 CHCN) Answer: Total # of C = 3 Total # of H = 3 Total # of N = 1 So the molecular formula is C 3 H 3 N
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3.2 Molecular Models Ball and Stick models : spheres represent atoms, sticks represent bonds Space Filling models : better represents molecules b/c the relative size of atoms are represented
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3.3 Ionic Compounds: Formulas, Names and Properties Ionic compounds : Made of ions, which are atoms that bear a positive or negative charge. Examples include NaCl and CaO. Ions : atoms that have gained or lost electrons. Two types : a. Cations: Atom loses electron, becomes positively charged (p #>e#) b. Anions: Atom gains electron, becomes negatively charged (p# <e#) Metals form cations, that is they have a tendency to lose electrons Nonmetals form anions, that is they have a tendency to gain electrons
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Monoatomic ions vs. Polyatomic ions Monoatomic ions: single atoms that have gained or lost electrons To determine the charge on a monoatomic ion, remember the following: 1. Metals of groups 1A -3A: Cations have a charge equal to the group of the metal to which they belong. 2. Nonmetals:
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This note was uploaded on 11/18/2010 for the course CHEMISTRY 4317 taught by Professor Cunycsichemistrydepartment during the Fall '08 term at Staten Island.

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Chapter 3 - 3.1 Molecules, Compounds and Formulas Molecule:...

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