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metal ppt (chemistry, bonding) trial one

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  • Good presentation and lots of effort .
    Try to do one for KS3 studens too- probably an earier to understand one.
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  • Metals

    1. 1. largest group of elements <ul><li>METALS </li></ul>
    2. 2. Mostly found as ORES combined with non-metal elements. Metal + non-metal = IONIC COMPOUNDS
    3. 3. IONIC COMPOUND <ul><li>Metal + Non-metal </li></ul>Stable? No Gain e- Give e- Share e- Metallic Lattice Metal
    4. 4. Useful properties that are not found in any other materials.
    5. 5. Metals are used where strength of a material is an important factor.
    6. 7. Why are metals lustrous? Why do we see a perfect (but laterally inverted) image in a plane mirror (silvered glass)?
    7. 8. metals covalent molecular covalent network covalent layer IONIC BONDING (microscopic) STRUCTURE & names (Symbolic) PROPERTIES (macroscopic)
    8. 9. METALS <ul><li>STRUCTURE </li></ul><ul><li>defines the </li></ul><ul><li>PROPERTIES </li></ul><ul><li>but </li></ul><ul><li>MODIFYING METALS </li></ul>
    9. 10. <ul><li>Larger in diameter, </li></ul><ul><li>so low/high electronegativity </li></ul><ul><li>Tend to lose/gain e- </li></ul><ul><li>Become cations/anions </li></ul><ul><li>More stable </li></ul>
    10. 11. Metal elements have: 1, 2 or 3 valence electrons. E.g. Magnesium 12: 2,8,2 To be stable they lose this last electron and become positively charged according to how many they lose 12p + Mg 2+
    11. 12. Since metal atoms have low electronegativities and they want to be more stable, the outer shell/ valence electron jumps out. These delocalised e-s form the pool/sea of delocalised e-s. (note: the language of pool/sea).
    12. 13. Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+
    13. 14. YOU DRAW
    14. 15. Mg 2+ METAL LATTICE Electrostatic attraction between CATIONS & Delocalised e- (sea of e-) (e-s free to move) Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+
    15. 16. <ul><li>Each sodium atom provides its one valence electron to form a ‘sea’ of delocalised electrons. </li></ul>Metallic bonding = electrostatic attraction between… … positive cations and delocalised electrons
    16. 18. PROPERTIES
    18. 20. E- can absorb quantum of energy and become excited When they fall back they release it as light Metal lattice contains ‘ Free’ e- = almost all differences of energy levels can be absorbed and re-emitted = almost all visible light reflected. = Lustrous (shiny) 1
    19. 21. Every electron can absorb a specific quantum or packet of radiation to become excited . &quot;Free&quot; electrons often absorb quanta of visible light. In metals the outer electrons are essentially &quot;free&quot; electrons and their energy depends on their distance from a nucleus; as there are countless &quot;free&quot; electrons of almost every possible extranuclear distance and energy they can absorb all the visible light that falls on the metal surface. However an excited electron re-emits the same absorbed quantum of radiation as it becomes de-excited and most of the radiation that is incident on a metal surface is expelled from the surface thus: metals are highly reflective or lustrous . 1
    20. 22. WHAT IS HAPPENING? (discuss) Good conductor of heat 2
    21. 23. Good conductor of heat <ul><li>When atoms absorb heat energy they vibrate (temperature is a measurement of molecular energy) and this vibration is passed from one atom to the next. </li></ul><ul><li>In metals, because the metal atoms are often close packed together the vibration or heating effect is passed rapidly through the metal from one atom to another. Also electrons are free to move so will bump and transmit this energy rapidly. </li></ul>2
    22. 24. Note: flow of current is the flow of positive charge, i.e. opposite direction of electron flow WHAT IS HAPPENING? (discuss) 3
    23. 25. Note: flow of current is the flow of positive charge, i.e. opposite direction of electron flow Current = flow of charge Sea of electrons = free to move 3
    24. 26. WHAT IS HAPPENING? (discuss) 4
    25. 27. <ul><li>Explains malleable and ductile nature of metals. </li></ul>4 Metallic Lattice Electrostatic attraction b/w cations and sea of electrons still present after deformation. Ionic Lattice Electrostatic attraction b/w cations and anions broken
    26. 28. High melting and boiling point To break the lattice the bonds must be broken. The electrostatic force between the sea of electrons and the cations is very strong. Thus it requires lots of energy, therefore it has high melting point and it is hard. (note: the more delocalised electrons the stronger these properties) The cations and electrons are closely packed together b/c strong… High density 5
    27. 29. Limitations of structure/properties Examples of some exceptions <ul><li>Mercury (low m.p.) </li></ul><ul><li>Co, Ni, Fe (magnetism) </li></ul>Chronium (brittle)
    28. 30. Properties (GENERALLY) <ul><li>Lustrous (Shiny when freshly cut or polished) </li></ul><ul><li>Good conductors of heat </li></ul><ul><li>Good conductors of electricity Malleable (can be shaped by heating) and Ductile (can be drawn into a wire) </li></ul><ul><li>Generally have high melting and boiling temperatures </li></ul><ul><li>Generally have high densities </li></ul><ul><li>High tensile strength – hard and tough and offer high resistance to the stresses of being stretched or drawn out and therefore do not easily break. </li></ul>
    29. 31. Ball bearing model <ul><li>Strength depends on arrangements of atoms in their crystal grains </li></ul><ul><li>Metals with rows in lattice distorted do not bend as easily. (rows do not slide as smoothly) </li></ul>
    30. 33. Grain : areas of perfect close-packing of cations <ul><li>Grain: areas of perfect close-packing. </li></ul><ul><li>Grain boundaries: boundaries b/w grains. </li></ul><ul><li>Grains are irregular shaped crystals of the metal pushed tightly together. </li></ul><ul><li>Small grain </li></ul><ul><li>Many dislocations and they do not bend easily = hard </li></ul><ul><li>less malleable = brittle </li></ul><ul><li>Large grains </li></ul><ul><li>Have fewer dislocations and they bend easily </li></ul><ul><li>malleable </li></ul>
    31. 34. MODIFYING METALS <ul><li>Work hardening </li></ul><ul><li>Heat treatment </li></ul><ul><li>Alloying </li></ul>
    32. 35. Work hardening <ul><li>Bending or hammering cold metals </li></ul><ul><li>Crystal grains become smaller </li></ul><ul><li>Metal is tougher (work hardened) </li></ul><ul><li>More brittle (e.g. keep bending a metal wire, it goes harder, then it snaps.) </li></ul>Bend a wire. What happens?
    33. 36. Heat treatment Consistent small crystals Smaller crystals Larger crystals Retains hardness, reduce brittleness. Quenched, warmed again to a lower temperature, cool slowly. Tempered Harder but more brittle (e.g. horseshoes) Heated to red hot, Cooled quickly (in cold water) Quenched Softer (restores ductility) Heated to red hot, cooled slowly Annealed
    34. 37. Alloying <ul><li>Combining a metal with other metals or some non-metals (Through melting and cooling the mixture) </li></ul><ul><li>Achieve alloy that has properties different from pure metals </li></ul><ul><ul><li>eg. Silver alloy is harder than silver, Solder (Pb and Sn) has lower melting temp. than Pb and Sn </li></ul></ul>
    35. 38. Ni-Cu alloy Magnetic alloys are at the heart of a wide range of technological applications from the oldest of structural materials to the next generation of data storage and retrieval devices.
    36. 39. Two types of alloys: <ul><li>Substitutional : atoms of metals are about the same size and replace each other in metal crystal </li></ul><ul><li>Interstitial : atoms of different size. Smaller atoms fit into the spaces between the larger atoms. </li></ul>