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Introduction to Ionic Compounds

Introduction to Ionic Compounds. Many ions have a noble gas configuration. Ions with a noble gas configuration are stable. A sodium atom has only one electron in its outer shell. Losing this electron produces an ion, Na + , with a noble gas configuration.

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Introduction to Ionic Compounds

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  1. Introduction to Ionic Compounds

  2. Many ions have a noble gas configuration Ions with a noble gas configuration are stable.

  3. A sodium atom has only one electron in its outer shell. Losing this electron produces an ion, Na+, with a noble gas configuration.

  4. A chlorine atom has 7 electrons in its outer shell. Adding one electron produces an ion, Cl-, with a noble gas configuration.

  5. Isoelectronic ions have the same electron configuration. • Many ions are isoelectronic with the noble gases. • These are the atoms found in the s and p blocks. • They follow the octet rule.

  6. Transition metals • Transition metals do not form ions that are isoelectronic with noble gases. • These metals often use d-orbital electrons in their bonding. • Some transition metals can form more than one cation. • e.g. Copper can form two ions, Cu+ and Cu2+. • Iron can form two ions, Fe2+ and Fe3+.

  7. Ionic substances form crystals held together by ionic bonds. • Notice that each ion is surrounded by ions of the opposite charge. • The ions are arranged such that the coulombic force of attraction is significantly greater than the force of repulsion.

  8. Formulas for Ionic Compounds • THERE IS NO SUCH THING AS AN IONIC MOLECULE. • Instead, formula units for ionic compounds are the simplest ratio of the ions. • e.g. The formula unit for sodium chloride is NaCl because there is one Na+ ion for every Cl- ion.

  9. Not all ionic compounds have the same structure. Note that each sodium ion is surrounded by 6 chlorine atoms, but each cesium atom is surrounded by 8 chlorine atoms. This structure is dictated by the relative size of the atoms.

  10. Lattice energy is the key to ionic bond formation. • Lattice energy is the energy released when ions (or atoms or molecules) come together to form a crystal. • The energy released is far greater than the energy required in the endothermic steps of separating molecules, converting them to a gaseous state, and ionization. • Energy is also released by gaining electrons, but not enough to drive the process.

  11. Properties of Ionic Compounds • Ionic crystals are hard and brittle. • Because of their repeating crystalline pattern, they cleave along planes. • Ionic compounds melt and boil at high temperatures. • Ionic solids do not conduct electricity, but liquid ionic compounds and solutions of ionic compounds do.

  12. Compare the orderly crystal arrangement of solid NaCl to molten and dissolved NaCl. • Ions in a solid are packed tightly and cannot move to conduct electricity. • Molten or dissolved ions are free to move and thus conduct electricity.

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