Properties of Metals and Alloys

Transcription

1 Properties of Metals and Alloys 1 of 19 Boardworks Ltd 2016

2 Properties of Metals and Alloys 2 of 19 Boardworks Ltd 2016

3 What is the structure of metals? 3 of 19 Boardworks Ltd 2016 Metal particles are held together by strong metallic bonds and are arranged in tightly packed layers, forming a regular lattice structure. The outer electrons of the metal atoms are detached and create a sea of electrons. These electrons are delocalised and are free to move through the structure. The metal atoms become positively charged ions and are attracted to the sea of electrons. This strong attraction is known as metallic bonding. sea of electrons metal ions

4 Metallic structures 4 of 19 Boardworks Ltd 2016

5 Properties of Metals and Alloys 5 of 19 Boardworks Ltd 2016

6 Electrons and metallic bonding 6 of 19 Boardworks Ltd 2016 How does the sea of electrons affect the properties of metals?

7 Why do metals have high melting points? 7 of 19 Boardworks Ltd 2016 The properties of metals are related to their structure. Metals often have high melting points and boiling points. Gold, for example, has a melting point of 1064 C and a boiling point of 2807 C. This is due to the strong attraction between the positively-charged metal ions and the sea of electrons. In metal extraction and other industrial processes, furnaces often run continuously to maintain the high temperatures needed to work with molten metals.

8 How do metals conduct heat? Delocalised electrons in metallic bonding allow metals to conduct heat. When a metal is heated, the delocalised electrons gain kinetic energy. These electrons then move faster and so transfer the gained energy throughout the metal. This makes heat transfer in metals very efficient. heat 8 of 19 Boardworks Ltd 2016

9 How do metals conduct electricity? 9 of 19 Boardworks Ltd 2016 Delocalised electrons in metallic bonding also allow metals to conduct electricity. The delocalised electrons are free to move through the metal structure. When a voltage is applied, the electrons flow through the metal and carry electric charge. Electrical conductivity relies on mobile charge. Therefore metals are good conductors of electricity. electricity

10 Why are metals strong? 10 of 19 Boardworks Ltd 2016 Metals are usually strong and not brittle. When a force is applied to a metal, the layers of metal ions are able to slide over each other, and so the structure does not shatter. metal before it is hit metal after it is hit force force The metallic bonds do not break because the delocalised electrons are free to move throughout the structure. This also explains why metals are malleable (easy to shape) and ductile (can be drawn into wires).

11 Properties of Metals and Alloys 11 of 19 Boardworks Ltd 2016

12 What is an alloy? 12 of 19 Boardworks Ltd 2016 An alloy is a mixture containing one or more metal elements. Steel is a common example of an alloy. It contains iron mixed with carbon and other elements. Adding other elements to a metal changes its structure and so changes its properties. The final alloy may have very different properties to the original metal. By changing the amount of each element in an alloy, material scientists can custom-make alloys to fit a given job.

13 Iron and steel 13 of 19 Boardworks Ltd 2016 Iron can be extracted from its ore in a blast furnace. The extracted iron is too soft for many uses and so it is mixed with other elements to make alloys, which are harder. The extracted iron is normally used to make steel. Steel is a lot stronger and harder than pure iron and is a very useful material. It can be used to make many things, from saucepans to suspension bridges.

14 Why is steel stronger than iron? 14 of 19 Boardworks Ltd 2016 The atoms in pure iron are arranged in densely-packed layers. These layers can slide over each other, making pure iron a very soft material. When other elements are added to iron to make steel, their atoms distort the regular structure of the iron atoms. This makes it more difficult for the layers of iron atoms to slide over each other, making the alloy stronger than pure iron.

15 Using metals and alloys 15 of 19 Boardworks Ltd 2016

16 Properties of Metals and Alloys 16 of 19 Boardworks Ltd 2016

17 Glossary 17 of 19 Boardworks Ltd 2016

18 Metallic bonding 18 of 19 Boardworks Ltd 2016

19 Multiple-choice quiz 19 of 19 Boardworks Ltd 2016