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 cubicEvery atom has 8 neighborsNa, K, Fe, Cr, W

Face-centered cubicEvery atom has 12 neighborsCu, Ag, Au, Al, Pb

Hexagonalclose-packedEvery atom has 12 Neighbors Mg, Zn, Cd

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