HARD-VS-SOFT-3 - 6. The softest of all cations are the...

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Figure 1: The periodic table, showing the metals (blue), metalloids (red), and insulators (yellow) 4. The hardest cations have a large positive charge, are electropositive, and small. The hardest cations are Al 3+ , Be 2+ , and Ti 4+ . Other hard ions include Li + and H + : they are small and electropositive. 5. Soft cations make strong bonds with soft anions. Soft cation-soft anion bonds have covalent character. Note a strong covalent bond requires elements which are close in electronegativity. Metal cations tend to be electropositive, while insulator anions tend to be electronegative. The recipe for a covalent bond is therefore an electronegative metal (think Au) and an elec- tropositive anions (think Te). See the electronegativity table below.
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Unformatted text preview: 6. The softest of all cations are the elements near Au. Gold is electronegative (and therefore will be able to make a good covalent bond with an electropositive anion). It is also a big element and is therefore very polarizable. Ag, Pt and Hg, the neighbors of Au are all very soft. 7. There is a second island of soft cations. Cs and Rb are quite soft. Although these cations are electropositive, they are big and oppy. Finally, they only have a single plus charge. Cs and Rb are not as soft as Au, Ag, Hg, Cu, or Pt. 8. Soft anions are large electropositive insulators and metalloids. Iodine and tellurium are both soft. 3...
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