1. Ch. 6.4
Bonding in Metals
Metallic Bonding

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

3. 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

4. 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”

5. 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

6. 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

7. 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

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

9. POINT > Describe metallic crystal structure

10. 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

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

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

13. 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

14. 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

15. 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)

16. 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)

17. 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

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