Section 7.4 Metallic Bonds and the Section 7.4 Metallic Bonds and the Properties of MetalsProperties of Metals

• Describe a metallic bond.

physical property: a characteristic of matter that can be observed or measured without altering the sample’s composition

• Relate the electron sea model to the physical properties of metals.

• Define alloys, and categorize them into two basic types.

Section 7.4 Metallic Bonds and the Section 7.4 Metallic Bonds and the Properties of Metals (cont.)Properties of Metals (cont.)

electron sea model

delocalized electron

metallic bond

alloy

Metals form crystal lattices and can be modeled as cations surrounded by a “sea” of freely moving valence electrons.

Metallic Bonds and the Properties of Metals

• Metals are not ionic but share Metals are not ionic but share several properties with ionic several properties with ionic compounds.compounds.

• Metals also form lattices in the solid Metals also form lattices in the solid state, where 8 to 12 other atoms state, where 8 to 12 other atoms closely surround each metal atom.closely surround each metal atom.

• Within the crowded lattice, the Within the crowded lattice, the outer energy levels of metal atoms outer energy levels of metal atoms overlap.overlap.

Metallic Bonds and the Properties of Metallic Bonds and the Properties of Metals (cont.)Metals (cont.)

• The electron sea model proposes The electron sea model proposes that all metal atoms in a metallic that all metal atoms in a metallic solid contribute their valence solid contribute their valence electrons to form a "sea" of electrons to form a "sea" of electrons.electrons.

• The electrons are free to move The electrons are free to move around and are referred to as around and are referred to as delocalized electrons, forming a delocalized electrons, forming a metallic cation.metallic cation.

Metallic Bonds and the Properties of Metals (cont.)

• A metallic bondA metallic bond is the attraction of is the attraction of an metallic cation for delocalized an metallic cation for delocalized electrons.electrons.

Metallic Bonds and the Properties of Metals (cont.)

• Boiling points are Boiling points are much more much more extreme than extreme than melting points melting points because of the because of the energy required energy required to separate atoms to separate atoms from the groups from the groups of cations and of cations and electrons.electrons.

Metallic Bonds and the Properties of Metals (cont.)

• Metals are Metals are malleablemalleable because they because they can be hammered into sheets.can be hammered into sheets.

• Metals are Metals are ductileductile because they can because they can be drawn into wires.be drawn into wires.

Metallic Bonds and the Properties of Metals (cont.)

• Mobile electrons around cations make Mobile electrons around cations make metals metals good conductors good conductors of electricity and of electricity and heat.heat.

• As the number of delocalized electrons As the number of delocalized electrons increases, so does hardness and strength.increases, so does hardness and strength.

• An alloy is a mixture of elements that has An alloy is a mixture of elements that has metallic properties. The properties of alloys metallic properties. The properties of alloys differ from the elements they contain.differ from the elements they contain.

Metal Alloys (cont.)• Substitutional alloys Substitutional alloys

are formed when some are formed when some atoms in the original atoms in the original metallic solid are metallic solid are replaced by other replaced by other metals of similar metals of similar atomic structure.atomic structure.

• Interstitial alloys Interstitial alloys are formed when are formed when small holes in a small holes in a metallic crystal are metallic crystal are filled with smaller filled with smaller atoms.atoms.

ChemistryChemistryMetallic Properties Mini-Metallic Properties Mini-

LAB:LAB:Spring steel Spring steel — iron with nickel as an alloy — iron with nickel as an alloy with carbon included.with carbon included.Special properties Special properties — resists stretching and — resists stretching and shattering; returns to its original shape after shattering; returns to its original shape after bending.bending.HardeningHardening—uses high heat; usually done —uses high heat; usually done first. Increases hardness but also the first. Increases hardness but also the brittleness.brittleness.TemperingTempering—uses lower heat; usually done —uses lower heat; usually done second increases toughness and????second increases toughness and????