MU #1 Physical properties of substances can be explained in terms of chemical bonds and intermolecular forces. These properties include conductivity, malleability, solubility, hardness, melting point, and boiling point.

Conductivity is the ability to carry an electrical current when electrons or ions are free to move.

Malleability is the ability of solids to be hammered into thin sheets.

Solubility is the ability to dissolve in a solvent.

Hardness is the ability to resist physical changes.

Melting point is the temperature at which a substance melts.

Boiling point is the temperature at which a substance boils.

Ionic solids such as NaCl(s) and CaI₂(s) have relatively strong ionic bonds between particles.

Example

NaCl(s)

Note: The crystal shape is cubic.

Their physical properties are:

• no conductivity because there are no free moving electrons or  ions, unless dissolved, NaCl(aq) or melted, NaCl(l)

• not malleable because particles cannot slide pass one another

• relatively high solubility

• relatively hard because ionic bonds are relatively strong

• high melting point because ionic bonds are relatively strong

• high boiling point because ionic bonds are relatively strong

Molecular (covalent) solids such as H₂O(s) and CO₂(s) have relatively weak intermolecular forces between molecules.

Example

H₂O(s)

Their physical properties are:

• no conductivity because there are no free moving electrons or  ions

• not malleable because particles cannot slide pass one another

• in general, relatively low or no solubility

• relatively soft because intermolecular forces are relatively weak

• low melting point because intermolecular forces are relatively weak

• low boiling point  because intermolecular forces are relatively weak

MU #2 Metallic bonds are formed when valence electrons are mobile.

Metals such as Cu(s) and Au(s) have metallic bonds between particles. Valence electrons in metals are not confined to each atoms but are shared by all. Therefore, positive ions (cations) are said to be immersed in a "moving sea" of electrons.

Example

Al(s)

Their physical properties of metals are:

• relatively high conductivity because there are free moving electrons

• malleable and ductile (can be drawn into thin wires)  because particles can slide pass one another

• relatively low solubility

• relatively hard because metallic bonds are relatively strong

• high melting point because metallic bonds are relatively strong

• high boiling point because metallic bonds are relatively strong

TEST YOUR UNDERSTANDING

8/07

1/07

6/06

1/06

6/02

1 Base your answers on the information below.

     Testing of an unknown solid shows that it has the properties listed below.

(1) low melting point

(2) nearly insoluble in water

(3) nonconductor of electricity

(4) relatively soft solid

    a) State the type of bonding that would be expected in the particles of this substance.

    b) Explain in terms of attractions between particles why the unknown solid has a low melting point. 

    c) Explain why the particles of this substance are nonconductors of electricity.

2 Metallic bonding occurs between atoms of   (1) sulfur              (2) copper              (3) fluorine                      (4) carbon

1/03

1 The high electrical conductivity of metals is primarily due to

                (1) high ionization energies   (2) filled energy levels   (3) mobile electrons  (4) high electronegativities

2  Which of the following solids has the highest melting point? (1) H₂O(s)       (2) Na₂O(s)     (3) SO₂(s)              (4) CO₂(s)

3 A chemist performs the same tests on two homogeneous white crystalline solids, A and B. The results are shown in the table below.

The results of these tests suggest that

(1) both solids contain only ionic bonds

(2) both solids contain only covalent bonds

(3) solid A contains only covalent bonds and solid B contains only ionic bonds

(4) solid A contains only ionic bonds and solid B contains only covalent bonds

6/03

1 Which substance contains metallic bonds? (1) Hg(l)  (2) H₂O(l) (3) NaCl(s) (4) C₆H₁₂O₆(s)

2 Which is a property of most nonmetallic solids?  (1) high thermal conductivity (2) high electrical conductivity (3) brittleness (4) malleability

1/04

32 The data table below represents the properties determined by the analysis of substances A, B, C, and D.

Which substance is an ionic compound? (1) A (2) B (3) C (4) D

6/04

6 Which statement describes a chemical property of iron?
        (1) Iron can be flattened into sheets. (2) Iron conducts electricity and heat.  (3) Iron combines with oxygen to form rust.  (4) Iron can be drawn into a wire.

12 Conductivity in a metal results from the metal atoms having
        (1) high electronegativity (2) high ionization energy
        (3) highly mobile protons in the nucleus (4) highly mobile electrons in the valence shell

8/04

9 Which characteristic is a property of molecular substances?

                (1) good heat conductivity (2) good electrical conductivity (3) low melting point (4) high melting point

1/05

37 A substance that does not conduct electricity as a solid but does conduct electricity when melted is most likely classified as

                (1) an ionic compound (2) a molecular compound (3) a metal (4) a nonmetal

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