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.

• 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’dMetals Ionic Compounds Molecular Compounds

Substance

MP (°C)

BP(°C)

Substance

MP(°C)

BP(°C)

Substance

MP(°C)

BP(°C)

Li 180 1347

CsBr 636 1300

H2 -259 -253

Sn 232 2623

NaI 661 1304

Cl2 -101 -34

Al 660 2467

MgCl2 714 1412

H2O 0 100

Ag 961 2155

NaCl 801 1413

C6H6 6 80

Cu 1083

2570

MgO 2852

3600

C6H12O6 142 Decompose

Table 6.4 on page 217

Nonmetal Properties

Molecular PropertiesNon-Polar

Polar

Covalent Networks

Diamond Graphite

Ionic SolidNaCl

MgO

Metallic Solids

Hg, Mecury

Ca, Calcium

Mechanical Properties of Solids

• Metals are malleable and ductile for the most part at room temperature.o Cu, Auo What about Hg?

• Ionic compounds are hard and brittle.o NaCl

• Molecular compounds can be solids at room temperature but they are very soft.o 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.o Only substance that are good electrical conductors in the solid state

are metals.o Ionic compounds are good conductors in liquid state or dissolved in

water.o 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.o 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