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1. Bonds are ionic when there is a large difference in electronegativities of the bonded atoms. Only c, e, and f are ionic.  Part a involves two of the same atoms bonded together – there is no difference in electronegativity, and therefore the bond is not ionic.  Parts b and d involve two atoms that are relatively close to each other on the periodic table, resulting in a low difference in electronegativity, implying that the bond is not ionic.

2. a. Li-F is stronger because it is an ionic bond while C-H is a covalent bond.  Ionic bonds are always stronger than covalent bonds.  Also notice that Li+ and F- are common ions, while C and H alone are not ions.  Ions come together as ionic bonds, and uncharged ions come together as covalent bonds.
b. Mg-O is stronger because Mg is charged 2+ and O is charged 2- while each ion in Li-F has only a charge of magnitude 1. Ions with higher charges are more strongly bound.  This can be verified with Coulomb’s law; energy is proportional to the strength of the constituent charges, and the 2+ and 2- charges will provide greater energy by a factor of four.  More bond energy means more energy is required to break the bond, which means the bond is stronger.
c. Li-F is stronger than Cs-I because the Li-F bond is far shorter than the Cs-I bond. By Coulomb’s law, energy is inversely proportional to the distance between the constituent charges, implying that shorter ionic bonds have greater lattice energy and are therefore harder to break and stronger.

3. a) A crystal lattice.  Simple molecules are typically covalent, and giant molecules are associated with large structures such as C(graphite), C(diamond) and Si.  In atomic theory, nuclei (protons and neutrons) are surrounded by clouds of electrons, not ions.

4. Ionic compounds form lattices because of the contributing attractions predicted by Coulomb’s law.  Each cation is surrounded by several anions and each anion is surrounded by several anions; the charges come together in such an attractive way that forms the predictable lattice.

5. Oppositely charged species attract each other, and lattice energy is proportional to the strength of the constituent charges and inversely proportional to the distance between those charges.

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