Section 8.4

1. Section 8.4 Metallic Bonds and Properties of Metals

2. Objectives • Describe a metallic bond • Explain the physical properties of metals in terms of metallic bonds • Defineanddescribe alloys

3. Key Terms • Electron sea model • Delocalized electrons • Metallic bond • Alloy

4. Metallic Bonds • Metals do not bond ionically with other metals • Metals form a crystal lattice similar to an ionic compound. • In the lattice the outer energy levels of the atoms overlap

5. Electron Sea Model • All the metal atoms in a metallic solid contribute their valence electrons to form a ‘sea’ of electrons

6. Delocalized Electrons • These valence electrons are not held by a specific atom and can move freely from atom to atom

7. Metallic Bond • Metals with wandering electrons become cations • The cations are attracted to the other atom’s delocalized electrons • This attraction is called a metallic bond

8. Properties of Metals • Metals are good conductors of heat or electricity • The delocalized electrons in a metal easily carry the heat or electricity through the metal • The delocalized electrons in metals also absorb and release electrons when exposed to light, giving metals their shiny luster.

9. Metal Alloys • An alloy is a mixture of elements that have metallic properties • Because of the nature of the metallic bond it is relatively easy to introduce other elements into the metallic crystal

10. 2 Types of Metal Alloys 1. Substitutional alloy -replaces metal atoms with atoms of similar size • Ex: copper atoms replace silver atoms in sterling silver 2. Interstitial alloy -fills in the gaps between metal atoms with smaller atoms • Ex: carbon atoms fill in the gaps between iron atoms in carbon steel

11. Homework • P. 231 #40-45 • P.237 #80-82,84