section 4 – pg 198 bonding in metals

Chapter 5

Section 4 – pg 198Bonding in Metals

Metals and Alloys• Alloy: a mixture made of two or more elements, at

least one of which is a metal• Alloys are generally stronger and less reactive than

the pure metals from which they are made Zinc + Copper = Brass Carbon + Iron = Steel

Copper + Silver = Sterling Silver

Pg 199

Physical Properties of Alloys• The properties of an alloy can differ greatly from those

of its individual elements– May also retain many physical properties of the metals

depending on how they are mixed

Pg 199

Chemical Properties of Alloys• The chemical properties of an alloy are different than

what it is made of– IE: Iron is strong and a good material to make tools out of

but it rusts so we add carbon to get steel, which is hard and does not rust

Pg 199

Iron rusts

Steel does not

Metallic Bonding• The properties of solid metals and their alloys can

be explained by the structure of metal atoms and the bonding between those atoms– Most metals have 1-3 valence electrons– These are held loosely and are easily lost causing the

metal atom to become positively charged

Pg 200

Metallic Bonding Continued• Metal atoms combine in regular patterns in which the

valence electrons are free to move from atom to atom– Crystalline Solids– Positively charged ions are closely packed together– Metallic Bond: an attraction between a positive metal

ion and the many electrons surrounding it

Pg 200

Metallic Properties• The “sea of electrons” model of metallic bonding

helps explain the malleability, ductility, luster. High electrical conductivity, and high thermal conductivity of solid metals

Pg 201

Malleability and Ductility• Metals are malleable (can be rolled into sheets or

beaten into shapes) and ductile (easily bent and pulled into thin strand or wire) because the positive ions are attracted to the loose electrons all around them rather than to the other metal ions– This is also why metals bend before breaking

Pg 201

Luster• A metals luster (shininess) is due to its valence

electrons– When light strikes these electrons, they absorb the light

and then give it off again

Pg 202

Electrical Conductivity• Metals conduct current easily b/c the electrons in a

metal can move freely among the atoms

Pg 202

Thermal Conductivity• Metals conduct heat easily because of the valence

electrons’ freedom of motion within a metal or metal alloy

Pg 202

Chapter 5 Section 4Homework – pg 203

1A. What is an alloy?

1B. From what pure metals is stainless steel made?

1C. Compare and contrast the general properties of alloys and

pure metals

2A. What is a metallic bond?

2B. Explain how metal atoms form metallic bonds. What role do the

valence electrons play?

2C. Review what you learned earlier about ionic bonds. How

does a metallic bond differ from an ionic bond?

3A. Name 4 properties of metals. What accounts for these

properties?

3B. In a light bulb, a thin tungsten wire filament that is wound in a coil

conducts electric current. Describe two properties of the metal tungsten that make it good material for the filament

3C. Why is it safer to use a nonmetal mixing spoon when cooking something

on a stove?