Properties of Compounds

1. Properties of Compounds

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

3. 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.

4. 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

5. 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!

6. 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.

7. 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

8. 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

9. 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