Bonding

Bonding - 13.1 13. Bonding (text Ch 13) There are two types...

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13.1 13. Bonding (text Ch 13) There are two types of chemical bonds: ionic and covalent. However, some bonds are frequently “in between.” A. Ionic Bonds In an ionic bond, at least one electron is completely transferred from one atom to another. If the ionic compounds are from main-group elements (not the transition elements), the ions have noble-gas configuration in their valence shells. Na + Cl Æ Na + Cl (Na + = [Ne] and Cl = [Ar]) Because of the strong electrostatic interactions between the cations and the anions, ionic compounds exist as crystal lattices at room temperature. Melting breaks the lattice. The force of attraction between the cation and the anion is dictated by Coulomb’s Law 2 2 1 Force r Q kQ = where the Q values are sizes of the charges on the ions and r is the distance between them. Which has a higher melting point, NaCl or LiF?
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13.2 B. Covalent Bonds 1. Structures Unlike ionic bonds, covalent bonding involves the sharing of electrons between atoms. It is assumed that only electrons in the valence shell are involved in the formation of covalent bonds. Suppose we have two H atoms forming molecular hydrogen: H( g ) + H( g ) Æ H 2 ( g ) Δ H = This is favourable because: o The two electrons in the bond are simultaneously attracted to both nuclei. o The pairing of electrons with opposite spin reduces the energy of the system We use electron-dot structures to show electrons and bonds: Each bond contains two electrons (one electron pair). In order for bonds to form, orbital overlap must occur. In this case, the 1 s orbital from each H atom overlaps.
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13.3 Since each H atom has the configuration 1 s 1 (one electron in the valence shell), it can only form one bond. O H H H H Cl H What if there is more than one electron in the valence shell, for example, with oxygen in water above? Such atoms can form more than one bond, but the exact number of bonds formed is predicted by Lewis structures . o The number of valence electrons surrounding a non- metal should be equal to a noble-gas structure. o For principle quantum number n = 2, recall that a full valence shell is 2 s 2 2 p 6 = 8 electrons = [Ne].
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This note was uploaded on 04/17/2008 for the course CHEM 020 taught by Professor Griffith during the Fall '07 term at UWO.

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Bonding - 13.1 13. Bonding (text Ch 13) There are two types...

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