TEKS 7D: Describe the nature of metallic bonding and apply the theory to explain metallic properties such as thermal and electrical conductivity, malleability, and ductility.

What is metallic bonding?What is metallic bonding?Metallic bonds are the forces of attraction between free-floating valence

electrons and positively charged metal cations.• In a metal, cations are packed closely together. • The loosely held valence electrons of the metal atoms form a “sea

of electrons” that drift freely from one part of the metal to another. • The overall charge of the metal is neutral.

1. Describe Describe the nature of metallic bonding. Include in your description an explanation of why a metal consists of cations rather than neutral atoms.

1. Describe Describe the nature of metallic bonding. Include in your description an explanation of why a metal consists of cations rather than neutral atoms.

TEKS 7D: Describe the nature of metallic bonding and apply the theory to explain metallic properties such as thermal and electrical conductivity, malleability, and ductility.

How does metallic bonding explain metallic properties?How does metallic bonding explain metallic properties?

Some common properties of metals include: • malleability—ability to be hammered or rolled into flat sheets or

other shapes• ductility—ability to be pulled out, or drawn, into wires• thermal conductivity—ability to transfer thermal energy in the form

of heat• electrical conductivity—ability to conduct an electric current

Each of these properties may be explained by applying the “sea-of-electrons” model of metallic bonding.

(contd.)(contd.)

TEKS 7D: Describe the nature of metallic bonding and apply the theory to explain metallic properties such as thermal and electrical conductivity, malleability, and ductility.

Malleability When a metal is subjected to pressure, the free-floating valence electrons shield the cations from one another. The cations easily slide past one another, so the metal changes shape rather than breaking apart, as an ionic crystal does.

(contd.)(contd.)

TEKS 7D: Describe the nature of metallic bonding and apply the theory to explain metallic properties such as thermal and electrical conductivity, malleability, and ductility.

Ductility As with malleability, pressure also may be exerted on metals by forcing them through the narrow opening of a die, for example. The metal changes shape but remains as one piece and emerges from the die as a wire.

As the wire is forced through the die, the size of

the opening in the die determines the diameter of

the wire.

(contd.)(contd.)

TEKS 7D: Describe the nature of metallic bonding and apply the theory to explain metallic properties such as thermal and electrical conductivity, malleability, and ductility.

Thermal conductivity Conduction is the transfer of thermal energy with no overall transfer of matter.

Conduction occurs within a material or between materials that are touching. Newton’s cradle is a device that helps explain conduction.

Newton’s cradle is a model for conduction. When a ball at one end is pulled back and released, energy is

transferred from one ball to the next, but only the last ball at the other end moves.

In metals, conduction is fast because the mobile valence electrons are free to move. Collisions of electrons transfer thermal energy through the metal.

(contd.)(contd.)

TEKS 7D: Describe the nature of metallic bonding and apply the theory to explain metallic properties such as thermal and electrical conductivity, malleability, and ductility.

Electrical conductivity An electric current is a flow of charged particles. Metals are good conductors of electric currents because the valence electrons can flow freely in the metal. As electrons enter one end of a piece of metal, an equal number of electrons leaves the other end.

2. Apply Theories Apply the theory of metallic bonding to explain the metallic properties of malleability and thermal conductivity of aluminum foil.

2. Apply Theories Apply the theory of metallic bonding to explain the metallic properties of malleability and thermal conductivity of aluminum foil.