Ch_322a_1.03

Ch_322a_1.03 - Chemical Bonds The first descriptions of the...

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Chemical Bonds The first descriptions of the nature of chemical bonds were put forward in 1916 by Gilbert Newton Lewis (1875-1946) and Walther Kossel (1888-1956). (Remember, the structure of the atom had been deduced only a few years earlier by Ernest Rutherford and Niels Bohr.) Two types of chemical bonds were recognized: (A) Ionic bonds are formed by the transfer of one or more valence-level electrons from one atom to another. Li . -e - Li + F : : . +e - F : : - Li + F - lithium fluoride (B) Covalent bonds are formed when atoms share valence-level electrons. F : . F : . + F : : F : fluorine Both types of bonds lead to electronic configurations around atoms that mimic a noble gas--filled outermost electronic levels.
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Ionic Bonds Li + F - lithium cation fluoride anion Electronegativity Electronegativity measures the tendency of an atom to attract electrons. Electronegativity increases in going left to right across a row in the Periodic Table. In some groups, it decreases in going down a column. Row 2 Li Be B C N O F increasing electronegativity Group 7 F Cl Br I decreasing electronegativity Ionic bonds are formed when atoms of very different electronegativities interact. When atoms lose or gain electrons, they develop charges and are called ions . Positively charged ions are cations , and negatively charged ions are called anions .
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Linus Pauling (1901-1994) Nobel Prize in Chemistry 1954 Nobel Peace Prize 1962 most electronegative least electronegative
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The electronegativity difference between interacting atoms determines the type of bond that is formed. compound
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Ch_322a_1.03 - Chemical Bonds The first descriptions of the...

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