Chap8 - Dr. Saidane Chem. 200 Lecture Notes CHAPTER 8, Part...

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Chem. 200 Dr. Saidane Lecture Notes CHAPTER 8, Part 1 Chemical Bonding There are three major types of chemical bonds: Ionic, covalent and metallic . Metallic bonds are bonds between metallic atoms. A metallic solid consists of cations surrounded by a sea of electrons. The nucleus and the inner shells (core) electrons represent the cation. The valence electrons represent the sea of electrons. The valence electrons are constantly moving from one atom to the other. The charge of the electron sea cancels the charges of the cations. The mobility of the sea of electrons makes metals conductor of electricity. Ionic bonds are bonds between metals or nonmetals. An ionic bond is the attraction between the opposite charges of cations and anions . When an ionic bond is formed, the valence electrons of the metal are transferred to the valence shell of the nonmetal. This transfer of electrons results in a complete (filled) valence shell for each of the atoms in the bond. Covalent bonds are bonds between two nonmetals. A covalent bond is a pair of electrons shared between two atoms . ELECTRONEGATIVITIY AND BOND POLARITY Ionic and covalent bonds are two extreme descriptions. All ionic bonds have some covalent character . Actual bonds lie somewhere between purely ionic and purely covalent. The electronegativity difference between two elements is an indication of the ionic or covalent character of a chemical bond . Electronegativity The electronegativity of an element is its electron pulling power when it is part of a bond . Electronegativity tends to be high towards the upper right corner of the periodic table and low on the lower left.
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Elements with low electronegativities are often called electropositive. An atom with a high electronegativity has a strong pulling power on electrons, particularly for the electron pair it shares with its neighbor. The outcome of the tug- of-war is that the more electronegative atom has a greater share in the electron pair of the covalent bond. Bonds formed between elements with a large difference in electronegativity tend to have significant ionic character in their bonding . Bond Polarizability and Polarity
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This note was uploaded on 09/09/2011 for the course CHEM 200 taught by Professor Saidane during the Spring '11 term at Mesa CC.

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Chap8 - Dr. Saidane Chem. 200 Lecture Notes CHAPTER 8, Part...

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