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Ionic Compounds and Ionic Bonds

Ionic Compounds and Ionic Bonds. Compounds composed of cations and anions are called ionic compounds. Ionic bonds – the electrostatic force that holds ions together in ionic compounds. Notice how the ions formed have the stable electron configuration of the octet of a noble gas.

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Ionic Compounds and Ionic Bonds

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  1. Ionic Compounds and Ionic Bonds Compounds composed of cations and anions are called ionic compounds. Ionic bonds – the electrostatic force that holds ions together in ionic compounds. Notice how the ions formed have the stable electron configuration of the octet of a noble gas.

  2. Formula unit – The lowest whole number ratio of ions in an ionic compound The coordination number of an ion is the number of ions of opposite charge that surround the ion in a crystal.

  3. Properties of Ionic Compounds 1. Usually a solid crystal at room temperature • Generally have a high melting point (for example NaCl mp = 800 degrees C) 3. Can conduct an electric current when melted or dissolved in water

  4. Bonding in Metals • Metals are made of closely packed cations, not neutral atoms • Valence electrons of metals can be modeled as a Sea of Electrons. • Metallic bonds are the attraction of the free floating valence electrons for the cations • High electrical conductivity – The large number of mobile electrons explains why metals have electrical conductivity several 100 times greater than a typical nonmetal. Ag is the best conductor.

  5. More about metallic bonds • Good conductor of heat – due to frequent collisions between the mobile electrons of metals • Ductile and malleable – the sea of electrons acts like a flexible glue, holding the nuclei together, so metal crystals can be deformed without shattering • Luster – most metals have a silvery white metallic color because they reflect light of all wavelengths. Because electrons are not restricted to a particular bond, they can absorb and re-emit light over a wide wavelength range.

  6. More metal facts • No metal dissolves in water, but the only liquid metal (at room T), mercury, dissolves many metals, forming solutions called amalgams. A Ag-Sn-Hg amalgam is used in filling teeth.) • Lowest melting point for metals is Hg at -39 C, and the highest is for tungsten at 3410 C.

  7. Metals are crystalline Metals are arranged in very compact and orderly patterns Hexagonal close-packed arrangement

  8. Face-centered cubic Every atom has 12 neighbors Cu, Ag, Au, Al, Pb Hexagonal close-packed Every atom has 12 Neighbors Mg, Zn, Cd Body-centered cubic Every atom has 8 neighbors Na, K, Fe, Cr, W

  9. Alloys are mixtures of 2 or more elements, at least one of which is a metal.

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