Properties of Compounds

Properties of Ionic Compounds Usually Crystalline Solids at Room Temperature Fluorite - CaF2 Barite – BaSO4 Wulfenite - PbMoO4

Properties of Ionic Compounds Each ion is strongly attracted to each of it’s neighbors These strong attractive forces result in a very stable structure This is reflected in the fact that ionic compounds generally have high melting points Going from a solid to a liquid (melting) requires adding enough energy to the atoms, ions, or molecules to overcome the attractive forces holding them together in a solid.

Properties of Ionic Compounds Melting point of some ionic compounds: Sodium chloride = 801C (1474F) Fluorite = 1403C Barite = 1508C Wulfenite = 1065C

Properties of Ionic Compounds Usually high solubility in water An electrolyte is a compound that conducts an electric current when it is dissolved in water or melted All ionic compounds are electrolytes Electrolyte demo!

Properties of Metals Metals are good conductors of electricity Metals are ductile – able to be drawn into wires Metals are malleable – able to be hammered or forced into shapes Ductility and malleability can both be explained by the “sea of electrons” model – When metals are subjected to pressure, metal cations easily slide past each other like ball bearings in oil. By contrast, if an ionic crystal is struck with a hammer, the hit pushes positive ions closer together , they repel each other, and the crystal breaks.

Properties of Metals Alloys – mixtures of 2 or more elements where at least one is a metal Alloys have properties that are superior to those of component elements Sterling silver is an alloy that is 92.5% silver and 7.5% copper Sterling silver is harder and more durable than pure silver Steels are important alloys today Steels contain a number of different elements (Fe, C, B, Cr, Mn, Mo, Ni, W, V) Steels are corrosion resistant, ductile, hard, and tough

Properties of Molecular Compounds Molecular compounds tend to have lower melting points and boiling points than ionic compounds Many molecular compounds are gases or liquids at room temperature Solids are often brittle Poor to non-conductor of electricity when dissolved in water Anywhere from high to low solubility in water

Properties of Network Covalent Compounds Melting a network covalent solid would require breaking covalent bonds throughout the solid Diamond, a network covalent solid, does not melt. Instead it vaporizes to a gas at 3500C Silicon carbide, another network covalent solid, melts at 2700C