L05EnegIonic145s10

L05EnegIonic145s10 - Lecture 5 spring 2010 ENGR 145 Chemistry of Materials Case Western Reserve University Lecture 5 Electronegativity Ionic

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Unformatted text preview: Lecture 5, spring 2010 ENGR 145: Chemistry of Materials Case Western Reserve University Lecture 5: Electronegativity; Ionic Bonding Reading assignment: OGC §3.2-3.7, 3.10, 3.11; C&R §2.5-2.6 Learning objectives: • Understand the concept of electronegativity and its relationship to ionization energies and electron afFnities • Understand ionic bonds as one extreme on the ionic- covalent continuum of bond character • Be able to compute the force and energy between ions in ionic bonds • Be able to determine the oxidation numbers of atoms in a given compound or polyatomic ion ENGR 145: Chemistry of Materials Case Western Reserve University Toward a Description of Chemical Bonds Ionization energy: energy of removing an e – to form a cation and Electron affinity: energy of adding an e – to form an anion These are properties of individual atoms / ions . Wanted: a single property to describe an element ʼ s tendency to attract, or surrender, electrons in molecules, compounds, alloys, … Lecture 5, spring 2010 ENGR 145: Chemistry of Materials Case Western Reserve University The tendency of an atom to draw electrons to itself in a chemical bond • Mulliken (1934) proposed a defnition: • Pauling (1932) proposed a defnition … • … based on actual bond energies • … widely used today, including here Electronegativity (OGC §3.4) χ Mulliken ∝ 1 2 IE 1 + EA ( ) Lecture 5, spring 2010 ENGR 145: Chemistry of Materials Case Western Reserve University Pauling’s Electronegativity: Trends • Typically increases … • from left to right in a row • from bottom to top of a column Increasing χ Increasing χ OGC Figure 3.7 Lecture 5, spring 2010 ENGR 145: Chemistry of Materials Case Western Reserve University Covalent vs. Ionic Character (OGC §3.7) • Competition over available electrons • Covalent bonding: sharing of electrons • Ionic bonding: transfer of electrons • Key distinction: where are the electrons located (electron density)? • For bonds between two different elements, both of these descriptions are idealizations, i.e. most real bonds are intermediate in character or − + + → e M M − − → + X e X Coulombic interaction M + X- Both M + and X – usually have full shells ENGR 145: Chemistry of Materials Case Western Reserve University Covalent vs. Ionic Character (OGC §3.7) • Competition over available electrons • Covalent bonding: sharing of electrons •...
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This note was uploaded on 01/30/2011 for the course EMSE 103 taught by Professor Ggh during the Spring '10 term at Case Western.

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L05EnegIonic145s10 - Lecture 5 spring 2010 ENGR 145 Chemistry of Materials Case Western Reserve University Lecture 5 Electronegativity Ionic

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