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Chapter 3

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CAS CH 111
Adrian Whitty

CHAPTER 3: CHEMICAL BONDING: THE CLASSICAL DESCRIPTION ■ quantum mechanics - the fundamental branch of physics that describes the properties, interactions, and motions of atomic and subatomic particles ﹣ used to explain the redistribution of electrons that forms chemical bonds ■ electronegativity - the tendency of an atom in a molecule to attract electrons from other atoms ﹣ explains whether a given pair of atoms form an ionic, covalent, or polar covalent bond ■ classical theory of bonding - using electrostatics to understand conceptual models of chemical bond ﹣ uses Lewis dot diagrams and VSEPR (valence shell electron-pair repulsion) theory 3.1 - REPRESENTATION OF MOLECULES ■ molecule - a collection of atoms bonded together ﹣ stable in gas phase and can form liquids and solids while preserving their identities ● Representations (appropriate for covalently bonded compounds by non-metallics) 1. Condensed structural formula a. ex: CH 3H 2H b. fails to show structure in 3D space 2. Lewis Dot Diagrams 3. Ball and Stick Model a. displays correct geometry 4. Space Filling Molecules a. shows the specific sizes of atoms that physically contact each other in molecules 5. Electrostatic Potential Energy Diagram/Elpot Diagram a. displays the electrostatic potential energy that a small positive test charge would experience at every position on the electron density surface that defines the space filling model b. good for evaluating chemical reactivity on different sites on molecules ● Isomers - different compounds that have the same molecular formulas, but differ in molecular structures and compounds ○ *properties of compounds are determined by the structures of their molecules* 3.2 - The Periodic Table ■ periodic law - the chemical properties of the elements are periodic functions of the atomic number Z (Z is increasing atomic number) ■ the periodic table is arranged by groups (vertically) and periods (horizontally) ﹣ there are 8 groups of representative element/main-group elements and 10 groups and 3 periods of transition metal elements ○ 57-71 are rare earth/lanthanide elements and 89-103 are actinide elements; these elements are unstable and usually produced artificially ● Survey of Physical and Chemical Properties: The Representative Elements ○ metals are characterized by their metallic luster, good conduction of heat and electricity, and malleability nonmetals are characterized by their lack of metallic luster, poor ability to conduct heat and electricity, and brittleness some elements have characteristics of metals and nonmetals and are called metalloids or semimetals [ex: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium] ○ Group I - Alkali Metals [Li, Na, Rb, Cs] ﹣ soft metals, low melting points, form 1:1 compounds with nonmetals ﹣ react with water to liberate H ○ Group II - Alkaline Earth Metals [Be, Mg, Ca, St, Ba, Ra] ﹣ form 1:2 compounds with halogens ○ Group III - include metalloid [B] and metals [Al, Ga, In, Ti] ﹣ form 1:3 compounds with chlorides and 2:3 compounds with oxides ○ Group IV - [C, Si, Ge, Sn, Pb] ﹣ Sn & Pb - metals with low melting points; Si & Ge - semiconductors ﹣ allotropes - modifications of an element with differing atomic arrangements that lead to different physical and chemical properties; very common for Carbon atoms ○ Group V - [N, P, As, Sb, Bi]
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