Chapter 6

1. Chapter 6 Metals

2. Why is all of this stuff important? Properties of elements determine what we can use them for. For example, tungsten has the highest melting point of any metal (34100C) but it is very ductile. For these reasons we use it in light bulbs as the filament.

3. Metal Atoms Metal atoms lose electrons to become stable. If there is a nonmetal around to bond with, they will give it their electrons and become part of a stable compound.

4. Metallic Bonds If there is not a nonmetal around, they have another solution. They become cations with free electrons floating around them. A metallic bond is the attraction between the cation and the free electrons around it.

5. Metallic Bonds The cations in a metal form a lattice (like the lines on graph paper) that is held in place by strong metallic bonds between the cations and the surrounding valence electrons. Because the total number of electrons does not change, the total metal is neutral.

6. Metallic Bonds Metallic bonds in some metals are stronger than in other metals. The more valence electrons in the shared pool, the stronger the metal will be. Alkali metals can only contribute 1 electron each to the pool so they are weak. Transition metals contribute more electrons so they are stronger.

7. Remember The stronger the metal, the higher its boiling point.

8. Metal Properties Metals’ properties are caused by the movement of electrons within the metal lattice.

9. Conductivity Metals conduct electric current. Electric current is a flow of charged particles. The pool of shared electrons in metals act like a reservoir for electric current to pass through.

10. Malleability Malleability is flexibility. The metal lattice is flexible compared to a rigid ionic compound lattice (remember those shatter when struck). When a metal lattice (a piece of metal) is struck, the ions shift slightly but do not break their metallic bonds. For this same reason, metals are ductile.

11. Alloys Alloys are mixtures of 2 or more elements (at least 1 of the elements must be a metal). Alloys have the properties of metals.

12. Types of Alloys Copper alloys Steel alloys Others

13. Copper Alloys Copper alone is a soft metal. Bronze = copper and tin Bronze is hard and durable. Brass = copper and zinc Brass is softer and shinier than bronze but not as durable.

14. Steel Alloys Steel = iron + carbon Carbon atoms fill in spaces in the iron lattice and add strength. Stainless steel = iron + chromium The chromium keeps the steel from rusting, but stainless steel is more brittle than steel containing carbon. Other steels contain sulfur, manganese, phosphorus, and/or silicon.

15. Other Alloys Alloys can be made to suit different needs based on what elements are added to them.

16. Why Alloys? Pure gold (24 karat) is easily worn and bent. Adding silver, copper, nickel, or zinc to gold (and reducing its karat or purity) makes it stronger and more durable.

17. Why Alloys? Aluminum is light but weak. When copper or manganese are added to aluminum it gains strength without gaining excessive weight. This is used to build airplane bodies.

18. Why Alloys? Magnesium burns when exposed to air. An aluminum-magnesium alloy stabilizes magnesium. This compound is used to make very lightweight airplane parts.

19. Why Alloys? Bridge cables need to resist stretching and pulling while supporting a great amount of weight. Special steel alloys are used for this.