The document discusses the key properties of metals and alloys. It covers the physical properties of metals, metallic bonding, and how alloys have different properties than their constituent elements due to their crystalline structure. The lesson objectives are to describe the properties of metals and alloys, explain metallic bonding, and why alloys are less malleable than pure metals.

1. METALS

2. Flow chart 1: The Periodic Table What has been taught ? The General Properties of metals Metals and Alloys What will be covered today? The Reactivity Series of metals -Order of reactivity -Reaction of Metals with water and dilute hydrochloric acid -Reduction of Metal oxides with carbon and hydrogen -The displacement reactions of metals -Reaction between a metal and the oxide of another metal What will be taught next lesson?

3. Atoms, Elements and Compounds Difference between Metals and Non-metals METALS Chemical Bonding: The Structure of Matter Metallic Bonding Acids and Bases Reactions of metals with acids Reactions of metal oxides and hydroxides Preparation Of Salt Reacting an acid with a metal The Periodic Table Alkali metals Transition metals Links between the chapter on metals and other chapters. Flow chart 2:

4. At the end of today’s lesson, students should be able to : State the physical properties of metals. Describe the general physical properties of metals as solids having high melting and boiling point, malleable, good conductor of heat and electricity in terms of their structure. Describe alloys as mixture of metal with another element. Give examples of alloys and state their uses. Write down the four main reasons for making alloys. Identify the representations of metals and alloys from diagrams of structures. 8. Explain why alloys have different physical properties to their constituent elements. Objectives

5. Good conductor of Heat Good conductor of Electricity Sonorous Can you think of what are some of the other physical properties of metals? What important property of metals is evident in each picture?

6. Can be bend and stretched without breaking Malleable and ductile Ease of Shaping Strong and tough Strength Usually high Density Solid (EXCEPT mercury, which is a liquid Physical State Usually high (except mercury and alkali metals) Melting and Boiling Point Shiny surfaces Appearance Metals Property Worksheet 1: Physical properties of Metals

7. Mercury Metal The element MERCURY (Hg) is the only metal which is liquid at room temperature! Melting Point (°C) -38.87 Boiling Point (°C) 356.9

8. Metallic Bonding Metals are held strongly to each other by metallic bonding. Atoms in the metals are held together by a ‘ sea of electrons’, which move freely among the positive metal ions arranged in a regular crystal lattice. Sea of electrons Positive ions TASK: Describe the general physical properties of metals in terms of their structure. + + + + + + + + + + + e e e e e e e e e e

9. Strong forces of attraction between the ‘sea of negatively charged electrons’ and the positive metal ions. High melting and boiling points Presence of free electrons carries heat and electricity energy. Good conductor of heat and electricity (in solid or molten state) Layers of metal atoms can slide over each other without disrupting the metallic bonding. Hence, metallic bonds are strong and flexible. Malleable (hammered into sheets) and Ductile (drawn into wires) without breaking Reason(s) Physical Properties The structure of Metal Push

10. Give three reasons why tungsten is used to make the filament inside an electric bulb? Reasons: (1) Tungsten can be drawn into very thin metal wires. (2) Tungsten has the highest melting point (3422 °C). (3) Tungsten has strong resistance to high temperature. Quick Wits

11. Is the above statement true? Answer: Not true “ All metals conduct heat and electricity and that non-metals do not.” “ All metals are good conductor of heat and electricity and that non-metals are poor conductor of heat and electricity.” Misconception

12. Over three quarter of the Periodic Table is made up of metals. Metals are useful materials in our everyday lives, from window grills to cooking pots and cars to other means of transport. Metals are undeniably important to us!

13. What do you think the objects in each picture are made of? Pure Gold? Pure Copper? Pure Iron? Pure metals have many useful properties but are not widely used. They are often too soft and have a low resistance to corrosion WHY?

14. How to make pure metals stronger and harder so that we can use them in our daily lives? By mixing two or more pure metals together Alloy - A mixture of a metal with another element. Metal + Metal Metal + Carbon (Non-metal) Alloy OR - Are made by mixing the molten elements (metals or carbon) in the right proportion and allowing them to solidify. Question

15. Join metals Solder 50% tin and 50% lead Trophies Bronze Copper and Tin Surgical instruments, window grills etc. Stainless steel 73% iron, 18% chromium, 8% nickel and 1% carbon Ornaments and souvenirs etc Pewter 97% tin, antimony (Sb) and copper Musical Instruments etc Brass 70% copper and 30% zinc Uses of Alloys Alloys Metals Examples and Uses of Alloys

16. Four main reasons for making alloys To improve the strength and hardness of metals. To improve the resistance of metals against corrosion and rusting. To improve the appearance of the metal. To lower the melting point of the metal.

17. Different-sized atoms Key: Pure metal atom Foreign atom (May be metal or non-metal Thinking Question 1: “ The physical properties of alloys are different from those of the elements they contain”. Give two examples to illustrate the statement. The structure of Alloys

18. Thinking Question 1: “ The physical properties of alloys are different from those of the elements they contain”. Give two examples to illustrate the statement. Explanation: Alloys are usually designed to have properties that are more desirable than those of the elements they contain. Properties such as strength and corrosion resistance may be considerably greater for an alloy than those of the elements they contain. As a result: Alloys are more widely used than pure metals. Solution: Steel is stronger than iron, one of its main elements. 2. Brass is more durable than copper , but more attractive than zinc.

19. Remark : It is more difficult to rearrange the atoms in an alloy. Remark: It is easy to rearrange the atoms in a pure metal. Structure of Alloys Structure of Pure metals Recall… Thinking Question 2: Explain why an alloy is less malleable than the pure metal. Different- sized atoms Large Push Push

20. Thinking Question 2: Explain why an alloy is less malleable than the pure metal. Hint: Recall how the atoms are arranged in the structure of pure metals and alloys. Alloys are strong and hard, not easily bent. Layers of atoms cannot slide over each other easily as foreign atoms are of different sizes and disrupt the orderly arrangement of metal atoms. Pure metals are soft and easily bent (malleable) because layers of atoms (of the same size) can slide over each other easily. This sliding movement of atoms is called a slip . Alloys Pure metals Solution: Malleable Can be beaten into thin sheets without breaking.

21. Summary What have been covered in this lesson? Metals are good conductors of heat and electricity whether in the solid or molten state. Metals usually have high melting, boiling points and densities. They are strong but can be bent, stretched or beaten into very thin sheets without breaking. Alloying is a technique involving the mixing of two or more metals to create an entirely new material with metallic effects. Four reasons for making alloys - Improve the strength and hardness of metals. - Improve the metals resistance against corrosion. - Improve the appearance of the metals. - Lower the melting point of the metals . Worksheet 2