Ch. 6.4 Bonding in Metals Metallic Bonding

POINT > Describe metal structure POINT > Describe “sea of electrons” model of metallic bonding POINT > Describe metallic crystal structure POINT > Define two types of alloys

POINT > Describe metal structure Metals consist of closely packed cations in a crystal structure Valence electrons drift freely from one part of the metal to another

POINT > Describe “sea of electrons” model of metallic bonding Metallic bonding is the attraction between free-floating valence electrons and positively charged metal ions “Sea of electrons”

WB CHECK: Metallic bonding occurs between metal anions and freely moving electrons positive and negative charged metal ions metal cations and freely moving electrons valence electrons of neighboring metal atoms

POINT > Describe “sea of electrons” model of metallic bonding Properties of metals are explained by the “sea of electrons” model: Good conductors: electrons move freely to carry charge

POINT > Describe “sea of electrons” model of metallic bonding Metals are ductile and malleable Subjected to pressure, metal cations can slide past each other because electrons are loose Ionic crystals shatter when subjected to pressure

POINT > Describe “sea of electrons” model of metallic bonding Ionic crystal Metal

POINT > Describe metallic crystal structure

POINT > Describe metallic crystal structure Metals are arranged in very compact & orderly crystal patterns 1. Body-Centered Cubic: Every atom has 8 neighbors Examples – Na, K, Fe, Cr, W Chromium

POINT > Describe metallic crystal structure 2. Face-Centered Cubic Every atom has 12 neighbors Examples – Cu, Ag, Au, Al, Pb Gold

POINT > Describe metallic crystal structure 3. Hexagonal Close-Packed Every atom has 12 neighbors Examples – Mg, Zn, Cd Zinc

WB CHECK: Metal structure can be described as loosely organized cations in a sea of electrons highly organized cations in a brittle structure loosely organized cations that are good conductors highly organized cations in a sea of electrons

POINT > Define two types of alloys Alloys are mixtures composed of two or more elements, at least one being a metal Alloy properties are often superior to the elements alone Examples: brass, bronze, sterling silver, steel

POINT > Define two types of alloys 1. Substitutional alloys: the atoms of the component elements are similar in size Atoms replace other atoms (ex. zinc atoms replace some copper atoms in brass)

POINT > Define two types of alloys 2. Interstitial alloys: atoms of the component elements are different in size Atoms fit between other atoms (ex. carbon atoms fit between iron atoms in steel)

WB CHECK: An alloy of sodium and gold would be a substitutional alloy a poor conductor of electricity an interstitial alloy impossible, since two metals cannot bond together

Homework: Read 185-6 S.A. #1-3 page 186 Continue prep for Exam 2