L08 - SUMMARY FROM LAST CLASS Ionic Bonding The atomic...

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Dr. P. Lucas U of A MSE 110 Ionic Bonding SUMMARY FROM LAST CLASS The atomic radius decreases along a period Cations are smaller and anions bigger than the corresponding atom. •T h e electronegativity is defined as the ability of an atom in a bond to attract electrons to itself. It increases along a period. The greater the difference in electronegativity between two atoms, the greater the ionic character of the bond. The ionic bond distance R o corresponds to the minimum bond energy at the equilibrium between electronic cloud repulsion and Coulombic attraction. The ionic bond strength decrease with ionic size. In the ionic solid, the charge of the anions must compensate the charge of the cations so that the composition is given by X n+ m L m- n . Ionic solids are brittle and have high melting points. Solvents of high dielectric constant ε like water decrease the Coulombic energy and dissolve ionic solids n rep R C E = R q q E o att πε 4 2 1 =
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Dr. P. Lucas U of A MSE 110 COVALENT BONDING Covalent bonding: electrons sharing. Atoms with similar electronegativity form covalent bonds. Electronic density plot of SCl 2 The electronic density is distributed along the bond between the two atoms. S Cl Cl Lewis electron dot diagram of SCl 2 The covalent bond is then described as two atoms combining or sharing two electrons to form a bond. This is done so as to satisfy the octet rule as described on the Lewis electrons dot diagram. They can not be distinguished as belonging to one or the other atom any more. Both electrons reside in a molecular orbital, equivalent to an atomic orbital but extending over several nucleus.
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L08 - SUMMARY FROM LAST CLASS Ionic Bonding The atomic...

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