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Iron(Metal)man • Why does Ironman appear to be shiny all over? • Why is it possible for Ironman to use metal as his costume? • Why does Ironman not get hurt easily?
Properties of Metal
– Will he melt easily? – Does he get burnt easily?
created by Janelle Tay (2010)
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Learning Objectives
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Structure of Metals
1. Describe the general properties of metals with respect to its structure.
The atoms are of the same sizes. created by Janelle Tay (2010)
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Physical properties of metals • • • • • •
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Physical properties VS structure • Physical properties of any substances are determined by the way its particles are packed • Atoms in a metal are packed regularly in layers
Solid at room temperature High density High melting and boiling points Malleable Ductile Good conductor of electricity and heat
created by Janelle Tay (2010)
created by Janelle Tay (2010)
– Held together by strong metallic bond • Metals have high densities, melting points and boiling points
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created by Janelle Tay (2010)
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Physical properties VS structure
Physical properties VS structure
Physical Property How is it related to the structure? High density
• Giant metallic structure • Atoms arranged in a regular and closely packed manner
Physical Property How is it related to the structure? High melting and • Atoms are held together by strong metallic boiling points bonds. • A lot of energy is required to break apart the strong metallic bonds in the giant lattice created by Janelle Tay (2010)
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Physical properties VS structure
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Physical properties VS structure
Physical Property Explanation Ductile and malleable
created by Janelle Tay (2010)
Atoms of the same size makes it easy for layers of atoms to slide over each other when force is applied
Physical Property High thermal and electrical conductivity
Explanation • Atoms are tightly packed but the outermost electrons of the atoms break away easily from the atoms – Positive (metal) ions are surrounded by the ‘sea of mobile electrons’
•The mobile electrons allow metals to conduct electricity. •Heat is also transferred easily by the mobile electrons in the structure.
created by Janelle Tay (2010)
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Sea of mobile electrons
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**NOTE: NOT all metals obey all the above physical properties mentioned. HOWEVER, ALL metals conduct electricity and this fact distinguish a metal from a non-metal.
Animation of sea of mobile electrons created by Janelle Tay (2010)
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created by Janelle Tay (2010)
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Pure metals • Useful properties but not widely used • This is because many pure metals
Most metallic substances used nowadays are ALLOYS!
– are soft – corrode easily (may react with air and water and wear away easily).
created by Janelle Tay (2010)
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created by Janelle Tay (2010)
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Learning Objectives 1. Define what an alloy is and give examples of alloys. 2. Identify representations of metals and alloys from diagrams of structures. 3. Explain why alloys are stronger than pure metals.
Alloys
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Alloys
Composition
Bronze
Copper and tin
Stainless steel
Iron, chromium, nickel and carbon
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Metals VS alloys
• An alloy is a mixture of a metal with one or a few other elements. Name of alloy
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Pure Metals 1. Soft and weak 2. Easily corroded 3. Loses metallic shine easily
Alloys 1. Hard and strong 2. Corrosion-resistant 3. Metallic shine is preserved
created by Janelle Tay (2010)
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Structure of metals and alloys
Structure of metals and alloys
• Structure: Atoms in pure metals are closely packed and regularly arranged. With force, the layers of atoms slide over each other, making the metal weak. This explains why metals are malleable and ductile.
• Structure: In an alloy, a foreign atom of another element is added into the pure metal. – Disrupts the orderly arrangement of the atoms of the pure metal – Makes it more difficult for the atoms to slide over each other – Makes the alloy stronger, – harder and less malleable Foreign atom
created by Janelle Tay (2010)
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created by Janelle Tay (2010)
Alloys
Alloys
• Hard and strong, less malleable • Improves appearance of the pure metal
• More resistant to corrosion
– Pewter (alloy of tin, antimony and copper) is used to make ornaments and souvenirs as it looks more attractive than pure tin
created by Janelle Tay (2010)
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– E.g. Copper corrodes easily so an alloy of copper is used to make coins
• Lower the melting point of metals – E.g. Solder (an alloy of tin and lead) has lower melting point hence is used to join metals
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created by Janelle Tay (2010)
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Metals
Use of alloys Alloy
Mixture of…
Uses
Brass
Copper and zinc
Electric plug, coins, Does not corrode musical instruments easily, attractive yellow colour like gold
Stainless steel
Iron, chromium and nickel
Cutlery, utensils, Resistant to corrosion medical instruments
Pewter
Lead, tin, some antimony
Souvenirs, ornaments
Bright, shiny colour like silver
Solder
Tin and lead
Joining metals
Low melting point
Bronze
Copper and tin
Propellers, ornaments
Less brittle, corrosion resistant
Pure metals
Alloys
Phys i cal Properti es
Phys i cal properti es
Special properties
High density
Hi gh melting a nd boi ling points
Ma l l eable
Ducti l e
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Good conductor of el ectricity a nd heat
Lower mel ting poi nt Ha rd, s trong and l es s malleable Res istant to corros i on
Alloys • Mixture of a metal with one or a few other elements • Made by mixing the molten elements (metals or metal and carbon) in the right proportions and allowing them to solidify created by Janelle Tay (2010) 24
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Exercise a(i)
Exercise a(ii)
• A positive ion, Mg2+, is formed when Mg atom loses 2 valence electrons. • Hence, the structure of magnesium metal consists of positive magnesium ions in a sea of mobile electrons. • These mobile electrons carry electric charges throughout the metal structure, therefore, conducting electricity.
• The structure of magnesium consists of atoms arranged in an orderly manner and are closely packed. • When a force is applied, the layers of atoms can slide over each other easily. • Therefore, it is malleable (can be beaten into thin sheets).
created by Janelle Tay (2010)
created by Janelle Tay (2010)
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