Metallic Bonds and Properties of Metals Chapter 8

Metallic Bonds and Properties of Metals Chapter 8 (p 228 -231) Chemistry Mr. Gilbertson

METALLIC BOND bond found in metals; holds metal atoms together very strongly

Metals �Metals consist of closely packed cations floating in a “sea of electrons”. �Valence electrons are said to be “delocalized” because they are not specifically associated with any one metal atom. �All of the atoms are able to share the electrons. �The electrons are not bound to individual atoms.

Cations maintain spacing due to mutual repulsion

Metallic Bond In a Sea of Delocalized Electrons

Properties of Metals �Melting points – vary greatly �Mercury – liquid at room temp �Tungsten – MP 3422 o C �Generally MP and BP are moderately high �MP not as extreme as BP, cations are mobile so not as much energy is required to move past one another �BP is higher because cations must be separated which takes much more energy

Properties of Metals �Metal cations can be pushed or pulled past each other �Ductile – can be drawn into wire �Malleable – can be hammered into sheets �Electrons act as a lubricant, allowing cations to move past each other �Durable – strong attraction to electrons

Properties of Metals �Conductivity of metals �Delocalized electrons are free to move �Movement of mobile electrons around cations allows an electric current to flow �When electrical potential is applied to a metal electrons are forced to metals have less “resistance” �Delocalized electrons move heat from one place to another much more quickly than in materials without mobile electrons

Properties of Metals �Luster – shiny when smooth and clean �Caused by interaction of mobile electrons and photons of light �Hardness and strength �Increases with an increase in the number of delocalized electrons. �Transition metals are generally harder (Cr, Fe, Ni) �Alkali metals are soft (only 1 delocalized electron)

Alloys �Mixtures of two or more elements, at least one of which is a metal. �Made by melting, mixing, then cooling the metals. �May contain non-metals like carbon.

Alloys �Properties are superior to their components. �Sterling silver � 92. 5% Ag, 7. 5% Cu �Harder than silver �Bronze � 7: 1 Cu to Sn (tin)

Alloys �Stainless Steel �Fe 80. 6%, Cr 18%, C 0. 4%, Ni 1% �Cast Iron -Fe 96%, C 4%

Types of Alloys �Two types of formation: �Substitutional alloys �Similar size atoms – replacement �Interstitial alloys �Different size atoms – smaller ions fill interstices (spaces between atoms)

Why is a metal ductile but an ionic compound is not?