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Structure Determines Properties. 6.3. Melting Points and Boiling Points. Metals and Ionic compounds to melt or boil, they must break the ionic or metallic bonds.
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Melting Points and Boiling Points • Metals and Ionic compounds to melt or boil, they must break the ionic or metallic bonds. • For molecular substances to melt or boil, the intramolecular covalent bonds between atoms do not break but, instead, intermolecular bonds between particles must break.
MP, BP Cont’d Table 6.4 on page 217
Molecular Properties Non-Polar Polar
Covalent Networks • Diamond Graphite
Ionic Solid • NaCl MgO
Metallic Solids Hg, Mecury Ca, Calcium
Mechanical Properties of Solids • Metals are malleable and ductile for the most part at room temperature. • Cu, Au • What about Hg? • Ionic compounds are hard and brittle. • NaCl • Molecular compounds can be solids at room temperature but they are very soft. • C12H22O11 (Sucrose), C20H42 (Parrafin wax)
Electrical Conductivity • The ability to conduct an electrical current requires that the negative and/or positive charges can move freely and independently of each other. • Only substance that are good electrical conductors in the solid state are metals. • Ionic compounds are good conductors in liquid state or dissolved in water. • Molecular compounds are not good conductors in any state except for graphite.
Thermal Conductivity • The same properties for why metals are good conductors of electricity is also why they are good thermal conductors. • This is the passing along of kinetic energy from an adjacent hot object or atom. The energy is passed on through the movement of electrons who with this new kinetic energy collide with other metal atoms near by and pass along the kinetic energy.
Questions • Page 225 Question 7 c) and d) • Page 226 Question 13