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.

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.

Properties of Ionic Compounds 1. Usually a solid crystal at room temperature 2.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

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.

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.

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.

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

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

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